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<task id="GUID-E93EE459-8CF4-42A1-B06C-E78E56FD25A0" xml:lang="en"><title>Listening

for Property Changes</title><shortdesc>The sensor channel APIs enable the client applications to be notified

about the changes to properties associated with a sensor channel.</shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody>

<prereq id="GUID-D1D22060-E453-4046-953D-10486D45885F"> Before listening for

the property changes of a sensor channel, you must <xref href="GUID-4B709839-8EEF-4AD2-9868-9AF0176B1E5B.dita#GUID-4B709839-8EEF-4AD2-9868-9AF0176B1E5B/GUID-FBBD3A8B-F240-4DC0-B516-3A51FDD86A88">open the sensor channel</xref>.         </prereq>

<context id="GUID-0D960123-7430-42B5-A84D-B63F2852DD7C"><p>The client applications

can use the property listener to monitor the property changes made by other

clients.</p></context>

<steps id="GUID-4DD07DEC-6017-4237-BE46-1D69E5FBD744-GENID-1-10-1-9-1-1-6-1-4-1-4-1-8-1-3-3">

<step id="GUID-9A69E5AD-E938-4092-A8C2-CB65C37C8962-GENID-1-10-1-9-1-1-6-1-4-1-4-1-8-1-3-3-1"><cmd>Create a property

listener implementation for the <parmname>MSensrvPropertyListener</parmname> interface.</cmd>

<stepxmp><codeblock xml:space="preserve">class PropertyListener:public MSensrvPropertyListener

    {

    public:    

    void PropertyChanged(CSensrvChannel &aChannel, const TSensrvProperty &aChangedProperty)

        {

        ...

         //Implementation

        }

    void PropertyError(CSensrvChannel &aChannel, TSensrvErrorSeverity aError)

        {

        ...

         //Implementation

        }

    void SetPropertySuccessIndicationChanged(TSetPropertySuccessIndicator aIndication)

        {

        ...

         //Implementation

        }

    void GetPropertyListenerInterfaceL(TUid aInterfaceUid, TAny *&aInterface)

        {

        ...

         //Implementation

        }

    };</codeblock></stepxmp>

</step>

<step id="GUID-6AB619B9-0259-493A-BC40-CAF5BF337E04"><cmd>Start property listening

by passing an instance of property listener implementation using <xref href="GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844.dita#GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844/GUID-4552066A-4FC1-3876-89AA-DC9B081B3814"><apiname>CSensrvChannel::SetPropertyListenerL()</apiname></xref>.</cmd>

<stepxmp><codeblock xml:space="preserve">//Instance of the property listener implementation

PropertyListener propListener;

...

CSensrvChannel* channel;

...

channel->SetPropertyListenerL(&propListener);

...</codeblock></stepxmp>

<info>When a property change occurs, a <parmname>PropertyChanged()</parmname> notification

is delivered through the <parmname>MSensrvPropertyListener</parmname> callback

interface to the clients that are listening for property changes.<note> The

client that set the property is not notified.</note></info>

</step>

<step id="GUID-8AD85E3B-EBBC-41E4-A32C-AF2A52B018E6"><cmd>Once you get the

required property changes associated with the sensor channel, you can stop

property listening by passing a NULL parameter to the <xref href="GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844.dita#GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844/GUID-4552066A-4FC1-3876-89AA-DC9B081B3814"><apiname>CSensrvChannel::SetPropertyListenerL()</apiname></xref> function.</cmd>

<stepxmp><codeblock xml:space="preserve">channel-&gt;SetPropertyListenerL();</codeblock></stepxmp>

</step>

</steps>