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<task id="GUID-BA0D9DA9-3B54-4964-A4D6-9ADA4DEB7231" xml:lang="en"><title>Receiving

Data from Sensors</title><shortdesc>You can implement a data listener to receive data from the sensors.

Based on the data received, you can perform specific actions on the Symbian

device. For example, if you receive information from the sensor about the

distance between the device and the user then based on this information, you

can disable or enable the loudspeaker mode on the Symbian device.</shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody>

<prereq id="GUID-E09C6ABC-F717-4791-A2EE-491421D2BD30">       <p>Before listening

for sensor channel data, 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>.</p>     </prereq>

<steps id="GUID-4DD07DEC-6017-4237-BE46-1D69E5FBD744-GENID-1-10-1-9-1-1-6-1-4-1-4-1-5-1-3-2">

<step id="GUID-CE0EE6EE-84A7-46F6-8590-C75FAA381843"><cmd>Implement the data

listener.</cmd>

<info><p>Inherit from the <parmname>MSensrvDataListener</parmname> interface

and implement the following pure virtual functions: <xref href="GUID-519E744E-246C-3F4A-A869-F25B03F1126F.dita#GUID-519E744E-246C-3F4A-A869-F25B03F1126F/GUID-92EDE76E-F5D8-3D45-939B-FD5C03347AE8"><apiname>MSensrvDataListener::DataReceived</apiname></xref>, <xref href="GUID-519E744E-246C-3F4A-A869-F25B03F1126F.dita#GUID-519E744E-246C-3F4A-A869-F25B03F1126F/GUID-F6C22940-A276-38C2-890F-CA45B75D613F"><apiname>MSensrvDataListener::DataError</apiname></xref> and <xref href="GUID-519E744E-246C-3F4A-A869-F25B03F1126F.dita#GUID-519E744E-246C-3F4A-A869-F25B03F1126F/GUID-4062844D-2F25-38FC-B91A-DD5B41E6FF3F"><apiname>MSensrvDataListener::GetDataListenerInterfaceL</apiname></xref></p><codeblock xml:space="preserve">class DataListener:public MSensrvDataListener

    {

    public:

        void DataReceived(CSensrvChannel& aChannel, TInt aCount, TInt aDataLost )

        {

        ...

         //Implementation

        }

    void DataError( CSensrvChannel&, TSensrvErrorSeverity)

        {

        ...

         //Implementation

        }

    void GetDataListenerInterfaceL( TUid, TAny*&)

        {

        ...

         //Implementation

        }

    };</codeblock></info>

</step>

<step id="GUID-107B26D8-CD5A-4571-8441-F1A5A2C0EB2B"><cmd>Start data listening.</cmd>

<info><p>Pass an instance of data listener implementation using the <xref href="GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844.dita#GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844/GUID-F851A108-C72F-3132-BE15-DC41CACB64F9"><apiname>CSensrvChannel::StartDataListeningL()</apiname></xref> function.</p><codeblock xml:space="preserve">//Instance of the data listener implementation

DataListener dataListener; 

...

CSensrvChannel* channel;

...

channel->StartDataListeningL(&dataListener, 1, 1, 0);

...</codeblock><p> When new data is available to be read in the sensor channel,

the client is notified by the <xref href="GUID-519E744E-246C-3F4A-A869-F25B03F1126F.dita#GUID-519E744E-246C-3F4A-A869-F25B03F1126F/GUID-7EE31046-31A6-356E-AFEF-2E8C003A7F15"><apiname>MSensrvDataListener::DataReceived(CSensrvChannel

&amp;,TInt,TInt)</apiname></xref> callback function. The channel data is received

into the receiving buffer. The receiving buffer is allocated from the heap

in the client's thread and its size is the channel data item size multiplied

by the maximum number of data items. </p></info>

</step>

<step id="GUID-40F9F566-475E-4ECD-B420-70EB1B77DEAA"><cmd>Read the channel

data from the receiving buffer using the <xref href="GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844.dita#GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844/GUID-EC1AF564-F05D-3729-B0C9-7573A1F79B86"><apiname>CSensrvChannel::GetData()</apiname></xref> function.

For more information about handling data notifications, see the following <xref href="GUID-BA0D9DA9-3B54-4964-A4D6-9ADA4DEB7231.dita#GUID-BA0D9DA9-3B54-4964-A4D6-9ADA4DEB7231/5876a529-0484-497d-8cf8-9ceb9c725388">Example</xref>.</cmd>

</step>

<step id="GUID-D3928C98-3D10-40BE-A63E-584969AA0416"><cmd>After you get the

required sensor data feeds from the sensor channel, you can stop data listening

using the <xref href="GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844.dita#GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844/GUID-0129F5FA-BD26-37F0-8FE4-19F393AA817C"><apiname>CSensrvChannel::StopDataListening()</apiname></xref> function.</cmd>

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

</step>

</steps>

<example id="5876A529-0484-497D-8CF8-9CEB9C725388"><p>The following example

shows how to handle the double tapping data notification that is received. </p><p>Check

the channel type of the received data and then receive the data object using

the <xref href="GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844.dita#GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844/GUID-EC1AF564-F05D-3729-B0C9-7573A1F79B86"><apiname>CSensrvChannel::GetData()</apiname></xref> function. The <parmname>aCount</parmname> parameter

provides the details about the number of data objects in the channels receiving

buffer. This number can be zero if the buffering period is used when data

listening is started. The <parmname>aDataLost</parmname> parameter provides

the details about the number of the lost data objects. For example, in heavy

load situations. </p><codeblock xml:space="preserve">void CTestClass::DataReceived( CSensrvChannel&amp; aChannel, 

                               TInt aCount, 

                               TInt aDataLost )

    {

    if ( aChannel.GetChannelInfo().iChannelType == KSensrvChannelTypeIdAccelerometerDoubleTappingData )

        {

        TSensrvTappingData tappingData;

        TPckg <TSensrvTappingData> tappingPackage( tappingData );

        aChannel.GetData( tappingPackage );

        }

    }</codeblock></example>

<postreq id="GUID-69071DC2-EB41-43BA-8DFC-CE2D4423AF8A"><p>End the session

with the sensor channel using the <xref href="GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844.dita#GUID-22DC917F-D833-3531-AB2D-A6E2D52EF844/GUID-0B8F50A6-2CA1-316A-82AB-AA026005E810"><apiname>CSensrvChannel::CloseChannel()</apiname></xref> function.</p></postreq>