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+++ b/Symbian3/SDK/Source/GUID-A30C1204-F130-501E-BD2D-1EE1537BEFC3.dita	Thu Jan 21 18:18:20 2010 +0000
@@ -0,0 +1,99 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<concept id="GUID-A30C1204-F130-501E-BD2D-1EE1537BEFC3" xml:lang="en"><title>How
+to implement a client interface with subsessions</title><shortdesc>Provides code snippets to help you to implement a
+client interface with subsessions.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>A client side subsession is represented by an instance of a class derived
+from <codeph>RSubSessionBase</codeph> which provides the behaviour for: </p>
+<ul>
+<li id="GUID-E82084CE-E5AF-56D8-934C-A183809532A2"><p>creating a subsession
+in the server </p> </li>
+<li id="GUID-F810EEC0-E0B1-52F1-9587-72BB41AD54C0"><p>sending messages to
+the subsession. </p> </li>
+</ul>
+<p>In the following code fragment, taken from the example that can be found
+at <filepath>...\examples\Base\IPC\ClientServer\complex</filepath>, the class <codeph>RCountSubSession</codeph>,
+derived from <codeph>RSubSessionBase</codeph>, represents the client side
+subsession with a server (in the example the server is also referred to as
+the count server). The assumption is made that the client has already established
+a session with the server as represented by the <codeph>RCountSession</codeph> class. </p>
+<codeblock id="GUID-C9F043AD-A44B-5EC8-9ED4-932747EB6C9B" xml:space="preserve">class RCountSubSession : public RSubSessionBase
+    {
+public:
+    TInt Open(RCountSession&amp; aServer);
+    TInt SetFromString(const TDesC&amp; aString);
+    void Close();
+    void Increase();
+    void Decrease();
+    void IncreaseBy(TInt anInt);
+    void DecreaseBy(TInt anInt);
+    void Reset();
+    TInt CounterValue();
+    };
+</codeblock>
+<codeblock id="GUID-7CE73750-213F-56EF-AEE5-04125147F934" xml:space="preserve">class RCountSession : public RSessionBase
+    {
+public:
+    RCountSession();
+    TInt Connect();
+    TVersion Version() const;
+    TInt ResourceCount();
+    void Close();
+private:
+    RThread iServerThread;    
+    };</codeblock>
+<p>The important points in this example are: </p>
+<ul>
+<li id="GUID-AC212539-94D5-515D-991A-1D9E2D756922"><p> <codeph>Open()</codeph> creates
+a subsession within the client-side session. A reference to the client-side
+session is specified as the function's single argument. The function calls <codeph>RSubSessionBase::CreateSubSession()</codeph> which,
+in turn, causes a server side subsession object to be created and its handle
+number to be returned. </p> </li>
+<li id="GUID-3762EF2B-D88B-5F8A-A0CD-C9D83ACEC208"><p>Client subsession interface
+functions, such as <codeph>CounterValue()</codeph>, send a specific message
+to the server. </p> <codeblock id="GUID-ABFAD354-7632-5FF5-A721-C95B0B8D29AD" xml:space="preserve">TInt RCountSubSession::CounterValue()
+    {
+    TInt res = KErrNotFound;
+    TPckgBuf&lt;TInt&gt; pckg;
+    
+    if (SubSessionHandle())
+        {
+          // Note that TPckgBuf is of type TDes8
+        TIpcArgs args(&amp;pckg);
+        SendReceive(ECountServValue, args);
+        
+          // Extract the value returned from the server. 
+        res = pckg();
+        }
+        
+    return res;        
+    }</codeblock> </li>
+</ul>
+<ul>
+<li id="GUID-64C2EC87-84BF-5892-AD04-40B8DDC0DEA0"><p> <codeph>Close()</codeph> closes
+the subsession. </p> </li>
+</ul>
+<section id="GUID-5E96565F-8D14-43AB-80A0-F6FD558F0073"><title>Notes</title> <ul>
+<li id="GUID-49CCA864-57FD-5E28-8890-F2A1CE707428"><p>The operation code passed
+to <codeph>RSubSessionBase::CreateSubSession()</codeph> must be interpreted
+by the server as a request to create a subsession. </p> </li>
+<li id="GUID-8F920E77-7FFF-5591-87A7-40BFE75A7649"><p>When sending a message
+to the server with a call to <codeph>RSubSessionBase::SendReceive()</codeph>,
+only three arguments can be passed . This function always uses the fourth
+argument to hold the client subsession handle number which is used to identify
+the corresponding server side subsession object. The message arguments are
+subsequently passed to a call to <codeph>RSessionBase::SendReceive()</codeph>. </p> </li>
+<li id="GUID-C690D49E-F5F0-5B71-BE11-5461556FF3A0"><p>The operation code passed
+to <codeph>RSubSessionBase::CloseSubSession()</codeph> must be interpreted
+by the server as a request to close the subsession. </p> </li>
+</ul> </section>
+</conbody></concept>
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