Using RProperty for subscribing

Article Metadata

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Tested with

Devices(s): Nokia N93

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Compatibility

Platform(s): S60 3rd Edition FP1 and later

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Article

Keywords: RProperty, RProperty::Define(), RProperty::Delete(), RProperty::Attach(), RProperty::Subscribe(), RProperty::Get(), RProperty::Cancel(), RProperty::Close()

Created: aknyman (15 Apr 2008)

Last edited: hamishwillee (14 Sep 2012)

Overview

This code snippet shows how the class RProperty can be used to subscribe user-defined properties published by Symbian's IPC Publish and Subscribe mechanism. The following steps are needed to subscribe and retrieve values of the updated properties.

• Register interest by attaching to the property with RProperty::Attach() and call RProperty::Subscribe().
• Get notified via a signal to the TRequestStatus to complete the RProperty::Subscribe().
• Retrieve the value of the updated property by calling RProperty::Get().
• Resubmit a request for notification of changes to the property by calling RProperty::Subscribe().
• Finally unsubscribe by calling RProperty::Cancel() and close the handle RProperty::Close().

The code snippet Archived:Using RProperty for publishing shows how these user-defined properties can be published. The property definitions are shared between a publisher and a subscriber through the common header file ExampleProperties.h.

#ifndef EXAMPLEPROPERTIES_H_
#define EXAMPLEPROPERTIES_H_
 
const TInt KMaxStrLen = 10;
const TUid KExampleProperty = {0xED1917A8};
enum TExamplePropertyKeys  { EIntProperty, EStrProperty };
 
#endif /*EXAMPLEPROPERTIES_H_*/

This snippet can be self-signed.

MMP file

The following libraries are required:

LIBRARY euser.lib

Preconditions

The publisher or the subscriber thread can be the one to define properties by calling RProperty::Define(). The user-defined properties persist in the kernel until the operating system reboots or the properties are deleted.

TInt ret=RProperty::Define(KExampleProperty,EIntProperty,RProperty::EInt);
if (ret != KErrAlreadyExists)
  {      
  User::LeaveIfError(ret);
  }
 
ret= RProperty::Define(KExampleProperty,EStrProperty,RProperty::EByteArray,KMaxStrLen);
if (ret != KErrAlreadyExists)
  {     
  User::LeaveIfError(ret);
  }

Header file

#ifndef EXAMPLESUBSCRIBER_H_
#define EXAMPLESUBSCRIBER_H_
 
//  INCLUDES
#include <e32base.h>
#include <e32property.h>
 
#include "exampleproperties.h"
 
 
class MExampleSubscriberObserver
{
public:
  virtual void IntPropertyUpdatedL(TInt aValue) = 0;
  virtual void StrPropertyUpdatedL(TDes& aValue) = 0;
};
 
 
class CExampleSubscriber : public CActive
        {
        enum {EPriority=0};
public:
        static CExampleSubscriber* NewL( const TUid aUid, 
                                    const TUint32 aKey,
                                    MExampleSubscriberObserver& aNotifier );
        virtual ~CExampleSubscriber();
 
private:
        CExampleSubscriber( const TUid aUid, const TUint32 aKey,
                                     MExampleSubscriberObserver& aNotifier );
        void ConstructL();
        void RunL();
        void DoCancel();
private:
      RProperty iProperty;
        const TUid iUid;
        const TUint32 iKey;
        MExampleSubscriberObserver&  iObserver; 
        };
 
#endif /*EXAMPLESUBSCRIBER_H_*/

Source file

#include "ExampleSubscriber.h"
 
CExampleSubscriber::CExampleSubscriber( 
        const TUid aUid, const TUint32 aKey,
        MExampleSubscriberObserver& aObserver )
            : CActive(EPriority), iUid( aUid ),
              iKey( aKey ), iObserver( aObserver)
        {
        }
 
CExampleSubscriber* CExampleSubscriber::NewL( const TUid aUid, const TUint32 aKey,
                               MExampleSubscriberObserver& aObserver )
        {
        CExampleSubscriber* self=
            new(ELeave) CExampleSubscriber( aUid, aKey, aObserver );
        CleanupStack::PushL(self);
        self->ConstructL();
        CleanupStack::Pop(self);
        return self;
        }
 
void CExampleSubscriber::ConstructL()
        {
        User::LeaveIfError( iProperty.Attach( iUid, iKey ) );
        CActiveScheduler::Add(this);
        // initial subscription and process current property value
        RunL();
        }
 
CExampleSubscriber::~CExampleSubscriber()
        {
        Cancel();
        iProperty.Close();
        }
 
void CExampleSubscriber::DoCancel()
        {
        iProperty.Cancel();
        }
 
void CExampleSubscriber::RunL()
  {
    // resubscribe before processing new value to prevent missing updates
    iProperty.Subscribe( iStatus );
    SetActive();
 
    TInt intValue;
    TBuf<KMaxStrLen> strValue;
 
    switch( iKey )
        {
        case EIntProperty: 
          // Int property updated, get new value
          //see also: RProperty::Get(KExampleProperty,EIntProperty,intValue);        
          if( iProperty.Get( intValue ) == KErrNotFound )
            {
              // Int property deleted, do necessary actions here...
                 }
             else
              {
              // use new value ...
              iObserver.IntPropertyUpdatedL(intValue);
              }
          break;
        case EStrProperty:
          // Int property updated, get new value
          //see also: RProperty::Get(KExampleProperty,EStrProperty,strValue);
          if( iProperty.Get( strValue ) == KErrNotFound )
            {
              // Str property deleted, do necessary actions here...
              }
          else
            {
              // use new value ...
              iObserver.StrPropertyUpdatedL(strValue);
              }
          break;
 
        default:
            break;
        }
  }
 
//  End of File

Using CExampleSubscriber class

• In the header file:

#include "examplesubscriber.h"
 
 
class CPropertyExampleAppUi : public CAknAppUi, MExampleSubscriberObserver
  {
//...
public:
  void IntPropertyUpdatedL(TInt aValue);
  void StrPropertyUpdatedL(TDes& aValue);
//...
  CExampleSubscriber* iIntSubscriber;
  CExampleSubscriber* iStrSubscriber;
        };

• In the source file:

void CPropertyExampleAppUi::ConstructL()
  {
//...
   iIntSubscriber = CExampleSubscriber::NewL(KExampleProperty,EIntProperty,*this);
    iStrSubscriber = CExampleSubscriber::NewL(KExampleProperty,EStrProperty,*this);
  } 
 
CPropertyExampleAppUi::~CPropertyExampleAppUi()
  {
//...
  delete iIntSubscriber; 
  delete iStrSubscriber;
  }
 
void CPropertyExampleAppUi::IntPropertyUpdatedL(TInt aValue) 
        {
  //do something with the updated property
        }
 
void CPropertyExampleAppUi::StrPropertyUpdatedL(TDes& aValue) 
        {
  //do something with the updated property        
  }

Postconditions

Two example properties are subscribed using the class RProperty.

If the subscriber thread defined the properties, it is also capable of deleting properties by using RProperty::Delete() as follows:

TInt err(KErrNone);
 
err = RProperty::Delete(KExampleProperty,EIntProperty);
if (err != KErrNotFound)
  {
  User::LeaveIfError(err);
  }
err = RProperty::Delete(KExampleProperty,EStrProperty);
if (err != KErrNotFound)
  {
  User::LeaveIfError(err);
  }

When properties are deleted, any outstanding subscriptions will be completed with KErrNotFound.

See also

Archived:Using RProperty for publishing