1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

     3 <!-- This component and the accompanying materials are made available under the terms of the License 

     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

     9 -->

    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-A30C1204-F130-501E-BD2D-1EE1537BEFC3" xml:lang="en"><title>How

    13 to implement a client interface with subsessions</title><shortdesc>Provides code snippets to help you to implement a

    14 client interface with subsessions.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>A client side subsession is represented by an instance of a class derived

    16 from <codeph>RSubSessionBase</codeph> which provides the behaviour for: </p>

    17 <ul>

    18 <li id="GUID-E82084CE-E5AF-56D8-934C-A183809532A2"><p>creating a subsession

    19 in the server </p> </li>

    20 <li id="GUID-F810EEC0-E0B1-52F1-9587-72BB41AD54C0"><p>sending messages to

    21 the subsession. </p> </li>

    22 </ul>

    23 <p>In the following code fragment, taken from the example that can be found

    24 at <filepath>...\examples\Base\IPC\ClientServer\complex</filepath>, the class <codeph>RCountSubSession</codeph>,

    25 derived from <codeph>RSubSessionBase</codeph>, represents the client side

    26 subsession with a server (in the example the server is also referred to as

    27 the count server). The assumption is made that the client has already established

    28 a session with the server as represented by the <codeph>RCountSession</codeph> class. </p>

    29 <codeblock id="GUID-C9F043AD-A44B-5EC8-9ED4-932747EB6C9B" xml:space="preserve">class RCountSubSession : public RSubSessionBase

    30     {

    31 public:

    32     TInt Open(RCountSession& aServer);

    33     TInt SetFromString(const TDesC& aString);

    34     void Close();

    35     void Increase();

    36     void Decrease();

    37     void IncreaseBy(TInt anInt);

    38     void DecreaseBy(TInt anInt);

    39     void Reset();

    40     TInt CounterValue();

    41     };

    42 </codeblock>

    43 <codeblock id="GUID-7CE73750-213F-56EF-AEE5-04125147F934" xml:space="preserve">class RCountSession : public RSessionBase

    44     {

    45 public:

    46     RCountSession();

    47     TInt Connect();

    48     TVersion Version() const;

    49     TInt ResourceCount();

    50     void Close();

    51 private:

    52     RThread iServerThread;    

    53     };</codeblock>

    54 <p>The important points in this example are: </p>

    55 <ul>

    56 <li id="GUID-AC212539-94D5-515D-991A-1D9E2D756922"><p> <codeph>Open()</codeph> creates

    57 a subsession within the client-side session. A reference to the client-side

    58 session is specified as the function's single argument. The function calls <codeph>RSubSessionBase::CreateSubSession()</codeph> which,

    59 in turn, causes a server side subsession object to be created and its handle

    60 number to be returned. </p> </li>

    61 <li id="GUID-3762EF2B-D88B-5F8A-A0CD-C9D83ACEC208"><p>Client subsession interface

    62 functions, such as <codeph>CounterValue()</codeph>, send a specific message

    63 to the server. </p> <codeblock id="GUID-ABFAD354-7632-5FF5-A721-C95B0B8D29AD" xml:space="preserve">TInt RCountSubSession::CounterValue()

    64     {

    65     TInt res = KErrNotFound;

    66     TPckgBuf<TInt> pckg;

    67     

    68     if (SubSessionHandle())

    69         {

    70           // Note that TPckgBuf is of type TDes8

    71         TIpcArgs args(&pckg);

    72         SendReceive(ECountServValue, args);

    73         

    74           // Extract the value returned from the server. 

    75         res = pckg();

    76         }

    77         

    78     return res;        

    79     }</codeblock> </li>

    80 </ul>

    81 <ul>

    82 <li id="GUID-64C2EC87-84BF-5892-AD04-40B8DDC0DEA0"><p> <codeph>Close()</codeph> closes

    83 the subsession. </p> </li>

    84 </ul>

    85 <section id="GUID-5E96565F-8D14-43AB-80A0-F6FD558F0073"><title>Notes</title> <ul>

    86 <li id="GUID-49CCA864-57FD-5E28-8890-F2A1CE707428"><p>The operation code passed

    87 to <codeph>RSubSessionBase::CreateSubSession()</codeph> must be interpreted

    88 by the server as a request to create a subsession. </p> </li>

    89 <li id="GUID-8F920E77-7FFF-5591-87A7-40BFE75A7649"><p>When sending a message

    90 to the server with a call to <codeph>RSubSessionBase::SendReceive()</codeph>,

    91 only three arguments can be passed . This function always uses the fourth

    92 argument to hold the client subsession handle number which is used to identify

    93 the corresponding server side subsession object. The message arguments are

    94 subsequently passed to a call to <codeph>RSessionBase::SendReceive()</codeph>. </p> </li>

    95 <li id="GUID-C690D49E-F5F0-5B71-BE11-5461556FF3A0"><p>The operation code passed

    96 to <codeph>RSubSessionBase::CloseSubSession()</codeph> must be interpreted

    97 by the server as a request to close the subsession. </p> </li>

    98 </ul> </section>

    99 </conbody></concept>