Symbian3/PDK/Source/GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita
author Graeme Price <GRAEME.PRICE@NOKIA.COM>
Fri, 15 Oct 2010 14:32:18 +0100
changeset 15 307f4279f433
parent 14 578be2adaf3e
permissions -rw-r--r--
Initial contribution of the Adaptation Documentation.
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<?xml version="1.0" encoding="utf-8"?>
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
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<!-- This component and the accompanying materials are made available under the terms of the License 
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"Eclipse Public License v1.0" which accompanies this distribution, 
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
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<!-- Initial Contributors:
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    Nokia Corporation - initial contribution.
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Contributors: 
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-->
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<!DOCTYPE concept
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D" xml:lang="en"><title>Publish
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and Subscribe</title><shortdesc>Publish and Subscribe allows global variables to be set and retrieved,
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and allows subscribers to be notified that variables have changed. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
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<p>The general pattern for using on the kernel side is almost the same as
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for the user side. However, different classes are used on the kernel side.
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It may be useful to compare kernel side usage with user side usage as described
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in the <xref href="GUID-A81C65CF-CF4E-571C-8080-9D387F46AAD6.dita">Publish and
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Subscribe</xref> guide for the user-side API. </p>
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<ul>
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<li id="GUID-BDAE8BFE-B0F9-5A3D-9E2B-6AC6280195E5"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-AD33A76A-9A27-5D66-B583-64F360EC996E">Properties</xref> </p> </li>
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<li id="GUID-3D892E85-C506-5FF6-A8E2-3A9458800CBB"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-E2261227-E747-53E0-9EE3-9CEC824C1832">Creating and closing a reference to a property</xref>  </p> </li>
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<li id="GUID-728CCCEB-8F5F-5CA1-A650-803C94E64194"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-C41886EF-24EC-58C2-A906-C4890CED3F3A">Defining a property</xref>  </p> </li>
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<li id="GUID-FB0EC3DC-38E1-5701-AF84-47A814238163"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-60F19D41-F9B5-5A21-9654-5D96CA6EE83E">Deleting a property</xref>  </p> </li>
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<li id="GUID-FAE51C6E-1C39-593C-B2AD-7BEFAA257F72"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-EBAA6B5C-CC73-5AE2-85CA-68B445828608">Publishing a property value</xref>  </p> </li>
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<li id="GUID-2F1A3E2F-44C8-5532-8FA2-F49A4FC58623"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-CA858A2A-4BF0-565D-8A6D-58AE32FEE304">Retrieving a property value</xref>  </p> </li>
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<li id="GUID-C39FCE8D-082E-56E8-85B2-137B25B88C61"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-984AB90D-FCCD-5383-B5D9-8D80AA83D989">Subscribing to, and unsubscribing from, a property </xref>  </p> </li>
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<li id="GUID-E02C9293-56B4-5AC0-9DA8-F47E6796A07D"><p> <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-21D8ADCA-9B39-5079-B4AD-FEBFCCB92049">Usage patterns</xref>  </p> </li>
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</ul>
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<section id="GUID-AD33A76A-9A27-5D66-B583-64F360EC996E"><title>Properties</title> <p>A
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property has the two attributes: identity and type. </p> <p><b>Identity</b> </p> <p>A
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property is identified by a 64-bit integer made up of two 32-bit parts: the
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category and the key. </p> <p>A property belongs to a category, and a category
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is identified by a UID. </p> <p>A key is a 32-bit value that identifies a
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specific property within a category. The meaning applied to the key depends
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on the kind of enumeration scheme set up for the category. At its simplest,
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a key can be an index value. It can also be another UID, if the category is
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designed to be generally extensible. </p> <p><b>Type</b> </p> <p>A property
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can be: </p> <ul>
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<li id="GUID-083AF1CA-ACA1-53A3-A251-370DD1D06554"><p>a single 32-bit value </p> </li>
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<li id="GUID-6EA61CFF-F549-5FA2-A6AA-43683C802B8D"><p>a contiguous set of
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bytes, referred to as a byte-array, whose length can vary from 0 to 512 bytes </p> </li>
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</ul><p>Once defined, a property value can change, but the property type cannot.
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Byte-array type properties can also change length provided the length does
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not exceed the value <xref href="GUID-C4776034-D190-3FC4-AF45-C7F195093AC3.dita#GUID-C4776034-D190-3FC4-AF45-C7F195093AC3/GUID-57E64054-610A-31D1-AD7F-E2F9F9FC1DCB"><apiname>RProperty::KMaxPropertySize</apiname></xref>. The limit
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on size of property ensures some limit on RAM usage. </p><p>The API allows
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a byte-array text type property to be pre-allocated when it is defined. This
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means that the time taken to set the values is bounded. However, if the length
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of this property type subsequently increases, then memory allocation may take
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place, and no guarantees can be made on the time taken to set them.</p><p>Note
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that the <xref href="GUID-C4776034-D190-3FC4-AF45-C7F195093AC3.dita#GUID-C4776034-D190-3FC4-AF45-C7F195093AC3/GUID-F8DE443B-B208-353C-A98E-AA52C4FE6530"><apiname>RProperty::ELargeByteArray</apiname></xref> property type can never
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provide a real-time guarantee. </p><p>For code running kernel side, properties
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and their values are defined, set and retrieved using a <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref> object.</p> </section>
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<section id="GUID-E2261227-E747-53E0-9EE3-9CEC824C1832"><title>Creating and
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closing a reference to a property</title> <p>On the kernel side, all accesses
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to a property <i>must</i> be done through a property reference, an instance
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of a <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref>. </p> <p>You must create a reference
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to a property, before doing any operation on that property. By operation,
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we mean defining a property, subscribing to a property, publishing and retrieving
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a property value. The kernel will fault if you have not first created a reference. </p> <p>Only
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one property, as uniquely identified by its category and key, can be accessed
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by an instance of <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref>; however a property can
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be referenced by more than one instance of <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref>. </p> <p>Internally,
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properties are represented by <codeph>TProperty</codeph> objects, and these
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are reference counted. The act of creating a reference to a property results
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either in the creation of a <codeph>TProperty</codeph> object or an increase
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in the reference count of an existing object. The property itself has no attributes
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or "structure" until it is defined. </p> <p>Please note that the structure
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and management of <codeph>TProperty</codeph> objects are part of Symbian platform's
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internal implementation and will not be discussed further. </p> <fig id="GUID-8A0D9C1E-00D7-5369-AD9C-28AA9151612F">
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<title>Objects internal to Symbian platform</title>
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<image href="GUID-31CE66F2-B36C-56ED-A399-BA9EFA179DED_d0e306443_href.png" placement="inline"/>
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</fig> <p>To establish a reference to a property, create an <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref> object,
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and then use one of the following functions: </p> <ul>
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<li id="GUID-87D76A73-6429-5D4C-8321-A98F756C30F5"><p> <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-DBEDDC3A-AE6F-3CAF-B251-4AA556EAF21C"><apiname>RPropertyRef::Attach()</apiname></xref> -
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tries to open the property identified by the category and key, if it exists,
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but creates that property if it does not exist. Creation is simply the act
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of creating the internal <codeph>TProperty</codeph> object. The object has
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no type or "structure" associated with it other than the use of the category
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and key as identification markers. </p> </li>
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<li id="GUID-7D1AFF17-BB0A-57B9-9782-001E983D9EDE"><p> <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-6F8EB0AB-C01A-3BFD-B334-D9C9FB923865"><apiname>RPropertyRef::Open()</apiname></xref> -
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tries to open the property identified by the category and key, and assumes
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that the property already exists; this fails if the property does not exist. </p> </li>
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</ul> <p>You can call these functions from a user thread running in supervisor
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mode, from a kernel thread or from a DFC. If calling from a user thread running
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in supervisor mode, then your thread must be running in a critical section.
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In debug mode, if a user thread is not in a critical section, then the kernel
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will fault. </p> <p>On successful return from these functions, the <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref> object
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owns a resource, the property, and this can then be defined and accessed through
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the <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref> object. </p> <p>It is difficult to make
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firm rules as to which one your code should use, but generally, you use <codeph>Open()</codeph> if
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you have no responsibility or interest in ensuring that the property exists.
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You would use <codeph>Attach()</codeph> if you were to have single or <i>joint</i> responsibility
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for ensuring that the property exists. It depends on the intent of the property
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and the role of your driver code in the system. </p> <p>Note that responsibility
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for creating the property does not necessarily align with who can define,
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delete, publish (write) or retrieve (read) a property value. This is governed
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by the intent of the property and, for retrieving and publishing, by the security
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policies in place. </p> <p>When the property is no longer needed, you can
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release it by calling <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-3465CD78-C107-3AD9-AEAF-F97A94C1C462"><apiname>RPropertyRef::Close()</apiname></xref>. Closing the
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reference does not cause the property to disappear. This only happens when
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the <i>final</i> reference to the property is closed. </p> <p>Note that it
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is quite legitimate to attach to, or to open, a property that has not been
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defined, and in this case no error will be returned either. This enables the
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lazy definition of properties as used in some of the usage patterns. </p> <codeblock id="GUID-7F4295E4-F822-5128-B4EC-3AD3E71BD444" xml:space="preserve">const TUid KMyPropertyCat={0x10012345};
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enum TMyPropertyKeys={EMyPropertyCounter,EMyPropertyName};
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. . .
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// Attach to the ‘counter’ property. This creates the property
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// if it does not already exist.
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RPropertyRef counter;
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TInt r;
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r=counter.Attach(KMyPropertyCat,EMyPropertyCounter);
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// r should be KErrNone if sucessful or KErrNoMemory if there
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// is an out of memory failure.
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if (r != KErrNone)
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    {
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    // Handle the bad return value
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    }
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// use the counter object...
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// when finished, release the property
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counter.Close();
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    </codeblock> </section>
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<section id="GUID-C41886EF-24EC-58C2-A906-C4890CED3F3A"><title>Defining a
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property </title> <p>Defining a property gives it "structure" i.e. attributes
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such as the property type, and the security policies that define the capabilities
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that a process must have to publish and retrieve the property value. </p> <p>A
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property is defined using the <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-47F367CB-E663-3F97-AC0C-31A9DD6BD5E5"><apiname>RPropertyRef::Define()</apiname></xref> function.
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You can call this function from a user thread running in supervisor mode,
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from a kernel thread or from a DFC. If calling from a user thread running
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in supervisor mode, then your thread must be running in a critical section.
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In debug mode, if a user thread is not in a critical section, then the kernel
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will fault. </p> <p>You can call this function from a user thread running
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in supervisor mode, from a kernel thread or from a DFC. If calling from a
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user thread running in supervisor mode, then your thread must be running in
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a critical section. In debug mode, if a user thread is not in a critical section,
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then the kernel will fault. </p> <p>The information needed to define the property
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is passed to <codeph>Define()</codeph>. Note that a reference to the property
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must already have been established using <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-DBEDDC3A-AE6F-3CAF-B251-4AA556EAF21C"><apiname>RPropertyRef::Attach()</apiname></xref> or <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-6F8EB0AB-C01A-3BFD-B334-D9C9FB923865"><apiname>RPropertyRef::Open()</apiname></xref>. </p> <p>A
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property does not need to be defined before it can be accessed. This supports
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programming patterns where both publishers and subscribers may define the
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property. </p> <p>Once defined, a property persists until the system reboots,
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or the property is explicitly deleted. Its lifetime is not tied to that of
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the thread or process that originally defined it. This means that, when defining
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a property, it is important to check the return code from the call to <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-47F367CB-E663-3F97-AC0C-31A9DD6BD5E5"><apiname>RPropertyRef::Define()</apiname></xref> to
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deal with the possibility that the property has previously been defined. </p> <p>The
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following code shows the definition of two properties, which we call: 'name'
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and 'counter': </p> <codeblock id="GUID-318DC2A6-FFE4-5781-9F78-5D5B4392585F" xml:space="preserve">const TUid KMyPropertyCat={0x10012345};
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enum TMyPropertyKeys={EMyPropertyCounter,EMyPropertyName};
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static _LIT_SECURITY_POLICY_PASS(KAllowAllPolicy);
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static _LIT_SECURITY_POLICY_C1(KPowerMgmtPolicy,ECapabilityPowerMgmt);
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TInt r;
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// Attaches to the ‘counter’ property. 
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// If the property already exists, a new reference to it is created.
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// If the property does not exist, it is created.
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RPropertyRef counter;
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r=counter.Attach(KMyPropertyCat,EMyPropertyCounter);
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if (r != KErrNone)
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    {
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    // Handle the bad return value
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    }
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// Attaches to the ‘name’ property. 
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// If the property already exists, a new reference to it is created.
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// If the property does not exist, it is created.
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RPropertyRef name;
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r=name.Attach(KMyPropertyCat,EMyPropertyName);
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if (r != KErrNone)
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    {
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    // Handle the bad return value
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    }
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// Now define the 'counter' property:
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// 1. Integer type
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// 2. Pre-allocated size has no meaning, and must be zero.
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// 3. Allow all processes to retrieve (read) the property.
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// 4. Only processes with power managament capability can write.
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// 5. Capability checks to be done against client thread's process.
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r=counter.Define(RProperty::EInt,KAllowAllPolicy,KPowerMgmtPolicy,0,iClientProcess);
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// You will probably need to check the return value.
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// It may legitimately by non-KErrNone.
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...
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// Now define the 'name' property:
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// 1. Byte array
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// 2. Pre-allocate 100 bytes.
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// 3. Allow all processes to retrieve (read) the property.
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// 4. Only processes with power managament capability can write.
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// 5. Capability checks to be done against client thread's process.
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r=name.Define(RProperty::EByteArray,KAllowAllPolicy,KPowerMgmtPolicy,100,iClientProcess);
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// You will probably need to check the return value.
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// It may legitimately be non-KErrNone.
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...</codeblock> <p>Once defined, a property value can change, but the property
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type cannot. Byte-array type properties can also change length provided the
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length does not exceed the 512 bytes, for <xref href="GUID-C4776034-D190-3FC4-AF45-C7F195093AC3.dita#GUID-C4776034-D190-3FC4-AF45-C7F195093AC3/GUID-19066DA4-B407-3C31-8472-371CA341BDC7"><apiname>RProperty::EByteArray</apiname></xref> types
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or 65535 bytes or <xref href="GUID-C4776034-D190-3FC4-AF45-C7F195093AC3.dita#GUID-C4776034-D190-3FC4-AF45-C7F195093AC3/GUID-F8DE443B-B208-353C-A98E-AA52C4FE6530"><apiname>RProperty::ELargeByteArray</apiname></xref> types. </p> <p>The
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API allows byte-array type properties to be pre-allocated when they are defined.
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This means that the time taken to set the values is bounded. However, if the
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length of these property types subsequently increases, then memory allocation
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may take place, and no guarantees can then be made on the time taken to set
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them. </p> <p> <b>Security notes:</b>  </p> <ul>
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<li id="GUID-E46B65DD-5D93-5796-8762-D8637947350D"><p>Symbian platform defines
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a property category known as the system category that is reserved for system
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services, and is identified by the <xref href="GUID-A85740BD-BC85-345E-B24A-92F68EA56270.dita"><apiname>KUidSystemCategoryValue</apiname></xref> UID.
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To define a property within this category, then the process on whose behalf
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your code is doing the define operation must have the <i>writeDeviceData</i> capability, <xref href="GUID-C607209F-6FC5-31DE-8034-E5B799B857A8.dita"><apiname>ECapabilityWriteDeviceData</apiname></xref>. </p> <p>To
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ensure that this security check is made, you must pass a pointer to the appropriate <codeph>DProcess</codeph> object
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as the second parameter to <codeph>Define()</codeph>. If you omit this parameter,
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a null pointer is assumed by default, and <i>the security check is bypassed</i>.
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This may be legitimate if you are doing this on behalf of the kernel or on
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behalf of the driver itself. </p> </li>
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<li id="GUID-18AA5E54-23AE-564F-BCB0-0F9FF70DEFD5"><p>Whether you pass a <codeph>DProcess</codeph> pointer
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or not, the owner of the property is deemed to be the process that is <i>current</i> when
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the code runs. It is this, the current process, that you will need to pass
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to <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-73FB49F1-E9EF-3CE3-A317-8888BAE49403"><apiname>RPropertyRef::Delete()</apiname></xref> at a later time. </p> </li>
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<li id="GUID-A941BD4F-E288-5A71-9F78-08351665AE73"><p>You also need to define
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two security policies: one to define the capabilities that will be required
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to publish (write to) the property, and the other to define the capabilities
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that will be required to retrieve (read) the property. Security policies are <xref href="GUID-81A285F6-3F87-3E77-9426-61BB16BC7109.dita"><apiname>TSecurityPolicy</apiname></xref> objects
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or their static equivalents. </p> <p>In the above code fragment, we specify
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that all processes in the system will be able to read the defined property
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but only those with power management capability will be able to write to the
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property - this is an arbitrary choice and is for illustration only. </p> </li>
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</ul> <p>In the above code fragments, <codeph>iClientProcess</codeph> is a
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pointer to the client thread's owning process object, and assumes that the
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driver code is making the request on behalf of a client, although this may
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not necessarily be so. Typically, if you need to keep this information, you
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could set this up in the logical channel constructor using the following code: </p> <codeblock id="GUID-33D0D5EA-8BB2-57DB-A327-D17A6A5C2D8E" xml:space="preserve">iClientProcess=&amp;Kern::CurrentProcess();</codeblock> <p>The
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constructor code runs in the context of the client user thread. Note that <codeph>DProcess</codeph> is
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internal to Symbian. </p> </section>
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<section id="GUID-60F19D41-F9B5-5A21-9654-5D96CA6EE83E"><title>Deleting a
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property </title> <p>Deleting a property is the opposite of defining it. It
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removes type and security information. It does <i>not</i> remove a reference
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to the property. </p> <p>A property is deleted using the <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-73FB49F1-E9EF-3CE3-A317-8888BAE49403"><apiname>RPropertyRef::Delete()</apiname></xref> function.
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You can call this function from a user thread running in supervisor mode,
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from a kernel thread or from a DFC. If calling from a user thread running
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in supervisor mode, then your thread must be running in a critical section.
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In debug mode, if a user thread is not in a critical section, then the kernel
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will fault. </p> <p>Any outstanding subscriptions for this property complete
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with <xref href="GUID-5E653C17-372C-32E1-A1B2-9E69A9991C40.dita"><apiname>KErrNotFound</apiname></xref>. </p> <p> <b>Security notes:</b>  </p> <ul>
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<li id="GUID-1B901363-70E9-560B-9C56-C63BB6D180C0"><p>Only the owning process
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is allowed to delete the property. This is deemed to be the process that was
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current when the property was defined. However, to enforce this, you <i>must</i> pass
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into <xref href="GUID-331FCC3D-B326-37A1-8AF5-381320224BBE.dita#GUID-331FCC3D-B326-37A1-8AF5-381320224BBE/GUID-2838E746-C917-3FB0-B2BA-464C38B5944B"><apiname>RPropertyref::Delete()</apiname></xref> a pointer to the <codeph>DProcess</codeph> object
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that represents the owning process. If you omit to pass this parameter to <codeph>Delete()</codeph>,
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a null pointer is assumed by default, and <i>the security check is bypassed.</i>.
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This may be legitimate if you are doing this on behalf of the kernel or on
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behalf of the driver itself. </p> </li>
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</ul> <p>For example, extending the code fragment introduced in defining a
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property above: </p> <codeblock id="GUID-25FBD12A-4461-5A92-9961-960DB26FE3F8" xml:space="preserve">const TUid KMyPropertyCat={0x10012345};
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enum TMyPropertyKeys={EMyPropertyCounter,EMyPropertyName};
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static _LIT_SECURITY_POLICY_PASS(KAllowAllPolicy);
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static _LIT_SECURITY_POLICY_C1(KPowerMgmtPolicy,ECapabilityPowerMgmt);
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TInt r;
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// Attaches to the ‘counter’ property. 
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// If the property already exists, a new reference to it is created.
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// If the property does not exist, it is created.
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RPropertyRef counter;
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r=counter.Attach(KMyPropertyCat,EMyPropertyCounter);
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if (r != KErrNone)
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    {
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    // Handle the bad return value
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    }
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// Attaches to the ‘name’ property. 
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// If the property already exists, a new reference to it is created.
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// If the property does not exist, it is created.
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RPropertyRef name;
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r=name.Attach(KMyPropertyCat,EMyPropertyName);
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if (r != KErrNone)
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    {
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    // Handle the bad return value
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    }
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// Now define the 'counter' property:
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// 1. Integer type
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// 2. Pre-allocated size has no meaning, and must be zero.
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// 3. Allow all processes to retrieve (read) the property.
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// 4. Only processes with power managament capability can write.
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// 5. Capability checks to be done against client thread's process.
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r=counter.Define(RProperty::EInt,KAllowAllPolicy,KPowerMgmtPolicy,0,iClientProcess);
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// You will probably need to check the return value.
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// It may legitimately by non-KErrNone.
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...
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// Now define the 'name' property:
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// 1. Byte array
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// 2. Pre-allocate 100 bytes.
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// 3. Allow all processes to retrieve (read) the property.
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// 4. Only processes with power managament capability can write.
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// 5. Capability checks to be done against client thread's process.
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r=name.Define(RProperty::EByteArray,KAllowAllPolicy,KPowerMgmtPolicy,100,iClientProcess);
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// You will probably need to check the return value.
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// It may legitimately by non-KErrNone.
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...
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// Delete the ‘name’ property.
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// Assumes that the owning process is iClientProcess. This will be checked
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// as being the valid owner of the property.
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r=name.Delete(iClientProcess);
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if (r != KErrNone)
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    {
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    // deal with a non-KErrNone return value.
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    }
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// Delete the ‘counter’ property.
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// Assumes that the owning process is iClientProcess. This will be checked
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// as being the valid owner of the property.
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r=name.Delete(iClientProcess);
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if (r != KErrNone)
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    {
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    // deal with a non-KErrNone return value.
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    }</codeblock> </section>
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<section id="GUID-EBAA6B5C-CC73-5AE2-85CA-68B445828608"><title>Publishing
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a property value </title> <p>A property is published (written), using the <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-D4B0220A-EB30-327C-B878-FBC5294A08F6"><apiname>RPropertyRef::Set()</apiname></xref> family
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of functions. </p> <p>This is guaranteed to have bounded execution time, suitable
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for high-priority, real-time tasks, except when publishing a byte-array property
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that requires the allocation of a larger space for the new value, or when
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publishing a large byte-array property type, as identified by <xref href="GUID-0B4D1D87-8C1B-3AEF-9C3D-3091FBDF3A6B.dita"><apiname>ELargeByteArray</apiname></xref>. </p> <p>Property
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values are written atomically. This means that it is not possible for threads
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reading a property to get a garbled value. </p> <p>All outstanding subscriptions
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for a property are completed when the value is published, even if it is exactly
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the same as the existing value. This means that a property can be used as
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a simple broadcast notification service. </p> <p>Publishing a property that
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is not defined is not necessarily a programming error. The <codeph>Set()</codeph> functions
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just return an error. If this is not expected for any particular usage, then
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the error must be checked and processed by the caller. </p> <p> <b>Security
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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notes:</b>  </p> <ul>
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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<li id="GUID-DA84723A-B9F7-525C-908A-BC51AA8B0366"><p>If you pass a pointer
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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to a <codeph>DProcess</codeph> object, then the capabilities of that process
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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will be checked against those contained in the write security policy that
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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was created and passed to <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-47F367CB-E663-3F97-AC0C-31A9DD6BD5E5"><apiname>RPropertyRef::Define()</apiname></xref>. If you
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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omit this <codeph>DProcess</codeph> parameter, a null pointer is assumed by
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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default, and <i>the security check is bypassed</i>. This may be legitimate
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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if you are doing this on behalf of the kernel or on behalf of the driver itself. </p> </li>
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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</ul> <p>See the code fragment in the section <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-CA858A2A-4BF0-565D-8A6D-58AE32FEE304">Retrieving
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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a property value</xref>  </p> </section>
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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<section id="GUID-CA858A2A-4BF0-565D-8A6D-58AE32FEE304"><title>Retrieving
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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a property value </title> <p>The current value of a property is retrieved
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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(read) using the <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-745E29E7-A26B-3207-ACA3-F8CC41FC7081"><apiname>RPropertyRef::Get()</apiname></xref> family of functions. </p> <p>This
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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is guaranteed to have bounded execution time, suitable for high-priority,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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real-time tasks, except when retrieving a large byte-array property type,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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as identified by <xref href="GUID-0B4D1D87-8C1B-3AEF-9C3D-3091FBDF3A6B.dita"><apiname>ELargeByteArray</apiname></xref>. </p> <p>Property values
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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are read atomically. This means that it is not possible for threads reading
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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a property to get a garbled value. </p> <p>Retrieving a property that is not
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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defined is not necessarily a programming error. The <codeph>Get()</codeph> functions
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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just return an error. If this is not expected for any particular usage, then
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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the error must be checked and processed by the caller. </p> <p>Integer properties
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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must be accessed using the overload that takes an integer reference, whereas
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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a byte-array property is accessed using the overload that takes a descriptor
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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reference. </p> <p>The following code fragment shows publication and retrieval
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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of a property. Note that it contains a race condition, especially if another
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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thread is executing the same sequence to increment the ‘counter’ value. </p> <p> <b>Security
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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notes:</b>  </p> <ul>
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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<li id="GUID-B117308F-416E-5BAE-880C-A162869799AD"><p>If you pass a pointer
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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to a <codeph>DProcess</codeph> object, then the capabilities of that process
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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will be checked against those contained in the read security policy that was
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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created and passed to <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-47F367CB-E663-3F97-AC0C-31A9DD6BD5E5"><apiname>RPropertyRef::Define()</apiname></xref>. If you omit
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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this <codeph>DProcess</codeph> parameter, a null pointer is assumed by default,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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and <i>the security check is bypassed</i>. This may be legitimate if you are
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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doing this on behalf of the kernel or on behalf of the driver itself. </p> </li>
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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</ul> <codeblock id="GUID-75549D12-A2CA-5039-BB91-2ABF19058DE5" xml:space="preserve">const TUid KMyPropertyCat={0x10012345};
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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enum TMyPropertyKeys={EMyPropertyCounter,EMyPropertyName};
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   386
TInt r;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   387
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   388
RPropertyRef counter;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   389
RPropertyRef name;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   390
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   391
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   392
// Assume that the 'name' and 'counter' property references have
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   393
// already been created. They may have been defined.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   394
//
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   395
// Assume that the process to be used for security checking is iClientProcess.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   396
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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diff changeset
   397
...
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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diff changeset
   398
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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   399
// publish a new name value. 
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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   400
_LIT8(KSomeExampleName,"My example name");
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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   401
r=name.Set(KSomeExampleName, iClientProcess);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   402
if (r != KErrNone)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   403
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   404
    // Check the return value. KErrNotFound means that the property has not yet been    
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
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   405
    // defined which may be legitimate.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   406
    // KErrArgument is a serious problem at this stage.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
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   407
    // KErrPermissionDenied is a security violation; the process iClientProcess has 
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   408
    // insufficient capability to do this operation. 
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   409
    }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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parents: 5
diff changeset
   410
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   411
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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   412
// Retrieve the first 10 characters of the name value.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   413
// We are not doing any security checking for this operation, so no DProcess pointer 
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
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   414
// is passed to Get(). 
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   415
TBuf&lt;10&gt; n;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   416
r=name.Get(n);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   417
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   418
if ((r!= KErrNone) &amp;&amp; (r != KErrOverflow))
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   419
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   420
    // Handle error value.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   421
    }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   422
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   423
// retrieve and publish a new value using the attached ‘counter’ property
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   424
TInt count;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   425
r=counter.Get(count);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   426
if (r==KErrNone)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   427
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   428
    r=counter.Set(++count);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   429
    }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   430
else
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   431
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
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   432
    // Handle bad return value
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   433
    }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   434
...
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   435
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   436
// When finised, release the property references.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   437
counter.Close();
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   438
name.Close();</codeblock> </section>
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   439
<section id="GUID-984AB90D-FCCD-5383-B5D9-8D80AA83D989"><title>Subscribing
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   440
to, and unsubscribing from, a property </title> <p>Subscribing to a property
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
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diff changeset
   441
is the act of making an asynchronous request to be notified of a change to
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
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diff changeset
   442
that property. </p> <p>You make a request for notification of a change to
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   443
a property by calling the <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-6DC06192-78AF-3B3D-8077-8479789AF006"><apiname>RPropertyRef::Subscribe()</apiname></xref> member
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   444
function on a property reference object. Only one subscription request can
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   445
be outstanding at any time for a given <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita"><apiname>RPropertyRef</apiname></xref> instance. </p> <p>You
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   446
can cancel an outstanding subscription request by calling <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-4AFB3074-E523-3404-8F0D-39995C35E045"><apiname>RPropertyRef::Cancel()</apiname></xref>.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   447
This is unsubscribing from the property. </p> <p>Subscribing to a property
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   448
is a single request to be notified when the property is next updated, it does
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   449
not generate an ongoing sequence of notifications for every change to that
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   450
property's value. Neither does it provide the caller with the new value. In
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   451
essence, the act of notification should be interpreted as “Property X has
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   452
changed” rather than “Property X has changed to Y”. This means that the new
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   453
value must be explicitly retrieved, if required. As a result, multiple updates
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   454
may be collapsed into one notification, and subscribers may not have visibility
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   455
of all intermediate values. </p> <p>This might appear to introduce a window
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   456
of opportunity for a subscriber to be out of synchronisation with the property
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   457
value – in particular, if the property is updated again before the subscriber
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   458
thread has had the chance to process the original notification. However, a
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   459
simple programming pattern, outlined in the second example below ensures this
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   460
does not happen. The principle is that, before dealing with a subscription
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   461
completion event, you should re-issue the subscription request. </p> <p>Note
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   462
that if the property has not been defined, then a subscription request does
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   463
not complete until the property is subsequently defined and published. Note
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   464
that the request will complete with <xref href="GUID-213DE05E-24F7-3E94-9B35-F4A72B3EBFD8.dita"><apiname>KErrPermissionDenied</apiname></xref> if
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   465
the subscribing process does not have sufficient capability as defined by
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   466
the <xref href="GUID-81A285F6-3F87-3E77-9426-61BB16BC7109.dita"><apiname>TSecurityPolicy</apiname></xref> object supplied by the process defining
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   467
the property. </p> <p>If the property is already defined, then the request
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   468
completes immediately with <xref href="GUID-213DE05E-24F7-3E94-9B35-F4A72B3EBFD8.dita"><apiname>KErrPermissionDenied</apiname></xref> if the
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   469
subscribing process does not have sufficient capability. </p> <p>The essence
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   470
of subscribing to a property is that you pass a function into <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-6DC06192-78AF-3B3D-8077-8479789AF006"><apiname>RPropertyRef::Subscribe()</apiname></xref> and
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   471
that this function is called when the property value is published. You pass
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   472
the function by wrapping it in <xref href="GUID-8A0F75CD-DC61-37EA-A23A-3A82080F0751.dita"><apiname>TPropertySubsRequest</apiname></xref> object
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   473
and then pass this into <codeph>Subscribe()</codeph>. What the function does
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   474
depends on the implementation, but you may want to re-subscribe to the property
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   475
and then retrieve the property value, or you may want to set some flag. It
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   476
all depends on the intent of the property and the driver code. </p> <p>The
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   477
following code fragments show the general idea. </p> <codeblock id="GUID-DF8201DF-7812-5B39-8B0F-3CB664BA00FA" xml:space="preserve">const TUid KMyPropertyCat={0x10012345};
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   478
enum TMyPropertyKeys={EMyPropertyCounter,EMyPropertyName};</codeblock> <codeblock id="GUID-2162EE7C-B834-50ED-9C84-3CE004C0B7D6" xml:space="preserve">class DMyLogicalChannel : public DLogicalChannel
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   479
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   480
    public :
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   481
        DMyLogicalChannel();
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   482
        void OpenReference();
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   483
        void SetUpSubscription();
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   484
        ...
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   485
    private :
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   486
        static void HandleSubsComplete(TAny* aPtr, TInt aReason);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   487
        ...
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   488
    private:
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   489
        RCounterRef iName;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   490
        TBuf&lt;10&gt;    iNameValue;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   491
        DProcess    iClientProcess;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   492
        TPropertySubsRequest iSubsRequest;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   493
        TInt iReason;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   494
    }</codeblock> <codeblock id="GUID-4A655D83-07CD-5998-A540-16D4A5EABFC5" xml:space="preserve">DMyLogicalChannel::DMyLogicalChannel() : iSubsRequest(&amp;HandleSubsComplete, this)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   495
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   496
    iClientProcess = &amp;Kern::CurrentProcess();
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   497
    // Other code omitted 
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   498
    }</codeblock> <codeblock id="GUID-DB6F4AF7-8866-50C5-95FD-5BCA1F2B55CE" xml:space="preserve">void DMyLogicalChannel::OpenReference()
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   499
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   500
    // Open a reference to the ‘name’ property, and assume that
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   501
    // the property has already been created and defined.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   502
  
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   503
    TInt r
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   504
    ...
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   505
    r=iName.Open(KMyPropertyCat,EMyPropertyName);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   506
    if (r != KErrNone)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   507
        {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   508
        // Handle bad return value.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   509
        }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   510
    ...
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   511
    }</codeblock> <codeblock id="GUID-217CFAF4-2CA6-588B-B3A2-667EB9A04FCA" xml:space="preserve">void DMyLogicalChannel::SetUpSubscription()
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   512
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   513
    // Now ask to be notified when the 'name' property is updated.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   514
    // This will eventually result in a call to the function HandleSubsComplete()
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   515
    // at some later time (asynchronously).
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   516
    // When eventually called, the pointer to this DMyLogicalChannel object will
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   517
    // be passed to HandleSubsComplete().
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   518
    //
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   519
    ...
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   520
    iReason = KRequestPending;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   521
    TInt r = iName.Subscribe(iSubsRequest); // ignoring security issues here.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   522
    if (r != KErrNone)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   523
        {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   524
        // handle bad return code.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   525
        }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   526
    return;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   527
    }</codeblock> <codeblock id="GUID-C2CD229F-F6CE-5EE3-9EBA-A69CED50FA07" xml:space="preserve">void DMyLogicalChannel::CancelSubscription()
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   528
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   529
    if (iReason == KRequestPending)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   530
        {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   531
        iName.Cancel(iSubsRequest);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   532
        }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   533
    }</codeblock> <codeblock id="GUID-D5E046B5-4D56-5B82-B4B8-D943DC601338" xml:space="preserve">void DMyLogicaChannel::SubsCompleteFn(TAny* aPtr, TInt aReason)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   534
    {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   535
    // A static function called when a change to the property occurs.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   536
    // aPtr will point to the DMyLogicalChannel object 
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   537
    // (see the DMyLogicalChannel constructor)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   538
    // aReason is the reason for the subscription completing. This may be:
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   539
    //     KErrNone - for a normal completion.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   540
    //     KErrPermissionDenied - if the security check has failed.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   541
    //     KErrCancel - if the request was cancelled.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   542
    // For a normal completion, setup another notification request before
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   543
    // getting the current value of the property.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   544
    //
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   545
    DMyLogicaChannel* self = (DMyLogicaChannel*) aPtr;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   546
       self-&gt;iReason = aReason;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   547
    if (iReason == KErrNone)
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   548
        {
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   549
        self-&gt;SetUpSubscription();
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   550
        self-&gt;Get(iNameValue,iClientProcess);
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   551
        return;
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   552
        }
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   553
    // Investigate the non-zero reason code.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   554
    }</codeblock> </section>
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   555
<section id="GUID-21D8ADCA-9B39-5079-B4AD-FEBFCCB92049"><title>Usage patterns</title> <p>There
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   556
are three usage patterns that can easily be identified, labelled as: standard
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   557
state, pure event distribution, and speculative publishing. </p> <p id="GUID-98103A8A-10E1-58FE-9613-A616E142AA2A"><b>Standard state</b> </p> <p>This
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   558
pattern is used for events and state that are known to be used widely in the
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   559
system. Examples of this might be battery level and signal strength, which
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   560
are important in every phone. </p> <p>The publisher calls <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-47F367CB-E663-3F97-AC0C-31A9DD6BD5E5"><apiname>RPropertyRef::Define()</apiname></xref> to
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   561
create the appropriate property. For byte array or text properties, a size
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   562
sufficient for all possible values should be reserved. An error of <xref href="GUID-D1D25122-F2B8-3C78-8599-84905BFD47B8.dita"><apiname>KErrAlreadyExists</apiname></xref> should
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   563
be ignored. The publisher then publishes the property values as, and when,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   564
appropriate. If the <codeph>RPropertyRef::Set()</codeph> call fails, this
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   565
should be treated as a serious error, since it indicates that important system
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   566
state is not getting through. Appropriate action might include panicking or
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   567
rebooting the system. Subscribers will use <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-6DC06192-78AF-3B3D-8077-8479789AF006"><apiname>RPropertyRef::Subscribe()</apiname></xref> to
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   568
request notification, and <codeph>RPropertyRef::Get()</codeph> to retrieve
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   569
the property value on notification. </p> <p>The memory to store the property
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   570
value will be permanently allocated, even if it turns out that no-one in the
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   571
system needs that value. This does ensure that the value can always be published,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   572
even if the system is in an out of memory situation. For this reason, this
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   573
approach should be limited to widely used and important state. The <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-8D9E6222-DDBA-55CA-A96F-1DCBD99E3FD3">Speculative publishing</xref> pattern offers an approach for dealing with
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   574
less important state. </p> <p id="GUID-5C82A92C-168D-5CD2-BE43-EE79AB500B14"><b>Pure event distribution</b> </p> <p>This
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   575
pattern is used when events need to be distributed, not values. </p> <p>The
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   576
publisher of the event simply uses an integer property, and calls <codeph>RPropertyRef::Set()</codeph> with
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   577
any value. Even if the value of the property is not changed by this operation,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   578
all subscribers will be notified that a <codeph>Set()</codeph> has occurred,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   579
and by implication that the related event has occurred. </p> <p>Subscribers
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   580
will be able to detect that an event has occurred, but will get no other information.
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   581
The minimum possible memory is wasted on storage for the dummy value. </p> <p id="GUID-8D9E6222-DDBA-55CA-A96F-1DCBD99E3FD3"><b>Speculative publishing</b> </p> <p>This
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   582
pattern is used when it is not known whether a value will be of interest to
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   583
others or not. Unlike the <xref href="GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D.dita#GUID-EBFD653D-6E6A-5F6F-88D7-8CCE07B4002D/GUID-98103A8A-10E1-58FE-9613-A616E142AA2A">standard
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   584
state</xref> pattern, the publisher of the event does not call <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-47F367CB-E663-3F97-AC0C-31A9DD6BD5E5"><apiname>RPropertyRef::Define()</apiname></xref> to
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   585
create the property. Instead, it simply calls <codeph>RPropertyRef::Set()</codeph> as
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   586
appropriate, and ignores any <xref href="GUID-5E653C17-372C-32E1-A1B2-9E69A9991C40.dita"><apiname>KErrNotFound</apiname></xref> error. </p> <p>When
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   587
other code in the system, i.e. a potential subscriber, is interested in the
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   588
state, it calls <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-47F367CB-E663-3F97-AC0C-31A9DD6BD5E5"><apiname>RPropertyRef::Define()</apiname></xref> to create the property
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   589
and allocate the memory for the value. An error of <xref href="GUID-D1D25122-F2B8-3C78-8599-84905BFD47B8.dita"><apiname>KErrAlreadyExists</apiname></xref> should
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   590
be ignored, as this only indicates that some other code in the system is also
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   591
interested in the value and has already created the property. </p> <p>The
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   592
subscriber then calls <xref href="GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2.dita#GUID-39D6B924-3FA3-39E6-A6EA-88E2D1927AC2/GUID-6DC06192-78AF-3B3D-8077-8479789AF006"><apiname>RPropertyRef::Subscribe()</apiname></xref> and <codeph>RPropertyRef::Get()</codeph> as
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   593
usual to interact with the property. On the first <codeph>Get()</codeph>,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   594
the subscriber may retrieve the property default value (zero, or a zero length
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   595
descriptor). This must be substituted with a sensible default value for the
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   596
property in question. </p> <p>Using this pattern, no memory is wasted on properties
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   597
that have no subscribers, while the publisher code is simpler as there is
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   598
no need for configuration as to which properties to publish. </p> <p>The publisher,
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   599
however, wastes some time attempting to publish unneeded values, but this
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   600
should not be an issue unless the value is very frequently updated. </p> <p>Where
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   601
events are published very infrequently, the subscriber could have a dummy
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   602
value for a long time, until the next publish event updates the value. Often
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   603
this is not a problem as a default value can be substituted. For example a
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   604
full/empty indicator for a battery level, none for signal strength etc. This
59758314f811 Week 23 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 2714, Bug 462.
Dominic Pinkman <dominic.pinkman@nokia.com>
parents: 5
diff changeset
   605
pattern is unlikely to be useful if there is no suitable default value. </p> </section>
1
25a17d01db0c Addition of the PDK content and example code for Documentation_content according to Feature bug 1607 and bug 1608
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
parents:
diff changeset
   606
</conbody></concept>