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  PUBLIC "-//OASIS//DTD DITA Task//EN" "task.dtd">
<task id="GUID-DCB8CA27-F64F-4B78-831D-F88B1AD7E38B" xml:lang="en"><title>Create
the client class</title><prolog><metadata><keywords/></metadata></prolog><taskbody>
<context>       <p>Create the client-side service support class, derived from <codeph>REikAppServiceBase</codeph>, <codeph>RApaAppServiceBase</codeph>, or a suitable System-GUI specialization of this class. This will have the
following responsibilities:</p> <ul>
<li><p>Implementing the client API </p></li>
<li><p>Organizing calls to and from the server over IPC</p></li>
<li><p>Any necessary security checks on the server. For example, restricting
the data sent to a server having particular capabilities.</p></li>
<li><p>Parameter checking from the server. Parameters returned from the server
application must be checked to ensure that they are valid.</p></li>
<li><p>Time-out support for IPC calls to the server.</p></li>
</ul><p>The reason for these checks is that the client cannot be sure that
the server application is using the appropriate server-side service support
classes and may instead be trying to weaken the system by implementing the
IPC handling itself.</p><p>This example shows the client interface for a chat
service implemented in two parts. The active object class <codeph>CChatter</codeph> is
the main client interface. It uses a class <codeph>RInterAppChat</codeph>,
derived from <codeph>REikAppServiceBase</codeph>, which handles the client-side
IPC for the chat service. </p><codeblock xml:space="preserve">class RInterAppChat : public REikAppServiceBase
    {
    public:
        TInt Send(const TDesC&amp; aMessage);
        void Receive(TRequestStatus&amp; aStatus, TDes&amp; aMessage);
        void CancelReceive();
    private:
        TUid ServiceUid() const;
    };
class MChatterReceiver
    {
    public:
        virtual void Receive(const TDesC&amp;) = 0;
    };
class CChatter : public CActive
    {
    public:
        CChatter(MChatterReceiver&amp; aReceiver);
        ~CChatter();
        void ConstructL(TUid aAppUid);
        void SendL(const TDesC&amp; aMsg);
    private:
        void Queue();
        void RunL();
        void DoCancel();
    public:
        RInterAppChat iSub;
        TBuf&lt;KMaxMyMessage&gt; iBuf;
        MChatterReceiver&amp; iReceiver;
    };</codeblock></context>
</taskbody></task>