Retrieving location information

Comments

16 Sep
2009

Article Review by sunil.shetty (20090916)

Very useful example for developers working on LBS applications. Provides the most basic goal of any LBS based application

i.e. constantly monitoring the location of the device.

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These classes demonstrates how to obtain information related to the current location of the mobile device.

Article Metadata

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Article

Created: Den123 (21 Apr 2008)

Last edited: hamishwillee (07 Feb 2012)

Headers required:

#include <lbs.h>
#include <lbspositioninfo.h>
#include <lbssatellite.h>

Link against:

LIBRARY  lbs.lib

Classes:

// helper class-observer
class MPositionReaderObserver
{
   public:
      // if successful reading
      virtual void ReadingComplete( TPositionInfoBase& aPosInfo ) = 0;
      // if error occurred
      virtual void ReadingError( TInt aErrorNo ) = 0;
};
 
// location info reader
class CPositionReader : public CActive
{
   public:	
      static CPositionReader* NewL( MPositionReaderObserver* anObserver );
      ~CPositionReader();
 
      // requests for reading
      void ReadPosInfo();
      void ReadCourseInfo();
      void ReadSatelliteInfo();
 
      // data access
      const TPositionInfo& PosInfo();
      const TPositionCourseInfo& CourseInfo();
      const TPositionSatelliteInfo& SatelliteInfo();
 
   public: // from CActive	          
      void RunL();
      void DoCancel();
 
   private:
      CPositionReader();
      void ConstructL( MPositionReaderObserver* anObserver );	  
      void ReadInternal( TPositionInfoBase& anInfo );
 
   private:	   	   
      MPositionReaderObserver* iObserver;
 
      // used to make the primary connection to the location server	   
      RPositionServer iServer;
      // used to create a sub-session with the server 
      RPositioner iPositioner;
 
      TPositionInfoBase*     iCurInfo;  // points to the current info
      TPositionInfo          iPositionInfo;          // location info
      TPositionCourseInfo    iPositionCourseInfo;    // course info
      TPositionSatelliteInfo iPositionSatelliteInfo; // satellites info
};

The body:

// factory
CPositionReader* CPositionReader :: NewL( MPositionReaderObserver* anObserver )
{
   CPositionReader* self = new (ELeave) CPositionReader();
   CleanupStack :: PushL( self );
   self->ConstructL( anObserver );
   CleanupStack :: Pop( self );	
   return self;
}
 
// c++ destructor
CPositionReader :: ~CPositionReader()
{
   Cancel();
   iPositioner.Close();
   iServer.Close();	
}
 
void CPositionReader :: ReadPosInfo()
{
   ReadInternal( iPositionInfo );
}
const TPositionInfo& CPositionReader :: PosInfo()
{
   return iPositionInfo;
}
 
void CPositionReader :: ReadCourseInfo()
{
   ReadInternal( iPositionCourseInfo );
}
const TPositionCourseInfo& CPositionReader :: CourseInfo()
{
   return iPositionCourseInfo;
}
 
void CPositionReader :: ReadSatelliteInfo()
{
   ReadInternal( iPositionSatelliteInfo );
}
const TPositionSatelliteInfo& CPositionReader :: SatelliteInfo()
{
   return iPositionSatelliteInfo;
}
 
void CPositionReader :: RunL()
{
   if( iStatus == KErrNone )
   {
      // location retrieved. Operation finished.
      iObserver->ReadingComplete( *iCurInfo );
   }
   else
      // error occurred 
      iObserver->ReadingError( iStatus.Int() );
}
 
void CPositionReader :: DoCancel()
{	
   // cancel update notify
   iPositioner.CancelRequest( EPositionerNotifyPositionUpdate );	
}
 
CPositionReader :: CPositionReader():
	CActive( CActive :: EPriorityStandard )
{
   CActiveScheduler :: Add( this );
}
 
void CPositionReader :: ConstructL( MPositionReaderObserver* anObserver )
{
   iObserver = anObserver;
 
    // connect to the location server
   User :: LeaveIfError( iServer.Connect() );
 
    // open the default positioner
   User :: LeaveIfError( iPositioner.Open( iServer ) );
 
   _LIT( KAppName, "YourAppName" ); // define your application name
   User::LeaveIfError( iPositioner.SetRequestor(
                          CRequestor :: ERequestorService,
                          CRequestor :: EFormatApplication,
                          KAppName ) );
 
   // set maximum allowed time for a location request
   const TInt KTimeout = 50000000; // 50 sec
   TTimeIntervalMicroSeconds timeOut( KTimeout );
   TPositionUpdateOptions updateOptions;
   updateOptions.SetUpdateTimeOut( timeOut );
   User::LeaveIfError( iPositioner.SetUpdateOptions( updateOptions ) );    
}
 
 
void CPositionReader :: ReadInternal( TPositionInfoBase& anInfo )
{
   iCurInfo = &anInfo;
 
   // prepare active object 
   Cancel();
   iStatus = KRequestPending;	
 
   // issuer request
   iPositioner.NotifyPositionUpdate( anInfo, iStatus );
   SetActive();
}

How to use:

• implement interface MPositionReaderObserver in your class
• include CPositionReader* iReader as a class member
• activate request:

iReader = CPositionReader :: NewL( this ); // new reader
iReader->ReadSatelliteInfo();   // request satellites info

• process results of reading:

void YourClass :: ReadingComplete( TPositionInfoBase& aPosInfo )
{
   TPositionSatelliteInfo& info = ( TPositionSatelliteInfo& )aPosInfo;
   TInt iSatellitesInView = info.NumSatellitesInView(); // count of satellites in view 
        iSatellitesUsed   = info.NumSatellitesUsed();   // count of used satellites
   ...
}

Related Links:

• Landmarks/web client example using Carbide.c++ and UI designer
• How to use Landmarks API
• How to select and show a landmark
• How to compact local landmark databases
• How to export landmarks from database to file
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• Execution of landmark operations
• How to obtain and save current location
• How to manage landmark categories