Using Extended Interfaces

Framework developers define and publish extension interfaces to the existing interfaces used in the framework. Once an interface extension is published by the framework developer, plug-in developers implement the extension if required.

1. 
   Identify the published instantiation and extended interface UIDs and header files of the framework.
2. 
   Create a new project file (.mmp) with targettype variable set as PLUGIN3. Allocate UIDs for the the plug-in implementations and plug-in DLL (UID3) as shown in the code snippet below.

   TARGET         cimplementationclass.dll
   TARGETTYPE     PLUGIN3
   CAPABILITY    All -TCB
   
   // PLUGIN3 recognition UID followed by the UID for this dll
   UID 0x10009D93 0x10009E37
   VENDORID 0x70000001
   
   SOURCEPATH    ../src
   SOURCE        cimplementationclass.cpp 
   
   USERINCLUDE    ../src
   SYSTEMINCLUDE     /epoc32/include
   
   START RESOURCE    cimplementationclass.rss
   TARGET cimplementationclass.rsc
   END
   
   LIBRARY     euser.lib
   LIBRARY     ecom.lib
   

3. 
   Create a new resource file (.rss) of format version 3.

   CImplementationClass.rss
   #include <ecom/registryinfov3.rh>
   
   RESOURCE REGISTRY_INFO theInfo
       {
       resource_format_version = RESOURCE_FORMAT_VERSION_3;
       dll_uid = 0x10009E37;
       interfaces = 
       {
       INTERFACE_INFO
           {
           instantiation_interface_uid = 0x10009DBB;
           implementations = 
           {
           IMPLEMENTATION_INFO
               {
               info_format = IMPLEMENTATION_INFO_RECORD_TYPE1; 
               implementation_uid = 0x10009E38;
               version_no = 1;
               display_name = "Extended Interface Example";
               default_data = {"Extended Interface Example||up to 255 chars", "Max. two strings allowed"};
               opaque_data = {"up to 255 chars", “max. 2 strings allowed”};
               extended_interfaces = {0x10009E44, 0x10009E45};
               flags = FLAG_ROM_ONLY;                    
               }    
           };
           }
       };
       }
   

4. 
   Implement the interfaces in the plug-in implementation source files. Implementing an interface extension in a plug-in implementation can be done in either of the two ways:
   1. 
      Inheritance: The instantiation interface object is also of the type of the extended interface object. When a user wants to instantiate the extended interface object, the implementation simply returns a re-cast of the instantiation interface object. The example below shows implementing an interface extension using inheritance.

      //Implementing an interface extension using multiple inheritance
      class CImplementationClass : public CExampleInterface, public MExampleInterfaceExtended
      {
      
      public:
          static CImplementationClass* NewL();
          static TAny* GetExtendedInterfaceL(TAny* aInstantiationInterface,const TUid& aExtendedInterfaceUid,TUint32& aBitFlags,TAny*& aReleaseObject);
          static void ReleaseExtendedInterface(TAny* aExtendedInterface, const TUid& aExtendedInterfaceUid);
      
          ~ CImplementationClass() {}
          virtual void DoMethodL(); // from original interface
          virtual void DoMethodExtended();  //from MExampleInterfaceExtended
      private:
          CImplementationClass() {}
      };
      
      

   2. 
      Realizing the extended interface as separate class and objects. When users fetch the extended interface object, the implementation allocates a new object. The example below shows implementing an interface extension using realisation.

      // Implementing an interface extension using realization
      
      class CImplementationClassExtended : public CBase, public MExampleInterfaceExtended2
      {
      public:
          static CImplementationClassExtended* NewL();
          ~ CImplementationClassExtended() {}
          virtual void DoMethodExtended2();  //from MExampleInterfaceExtended2
      private:
          CImplementationClassExtended() {}
      };
      

5. 
   Implement REComSession::CreateImplementationL(),REComSession::GetExtendedInterfaceL(),REComSession::ManuallyReleaseExtendedInterfaceL() functions of the instantiation interface.

   TAny* CImplementationClass::GetExtendedInterfaceL(TAny* aInstantiationInterface,
   const TUid& aExtendedInterfaceUid,
   TUint32& aBitFlags,
   TAny*& aReleaseObject)
       {
       TAny* ret = NULL;
       aBitFlags &= ~KReleaseRequiredMask; // clear release flag
       switch (aExtendedInterfaceUid.iUid)
       {
       case 0x10009E44: 
           {
               // release not required, so do not modify aBitFlags.
            // re-cast Instantiation object as Extended Interface object
           ret = static_cast<MExampleInterfaceExtended *> (static_cast<CImplementationClass *>(aObject));
           break;
           }    
       case 0x10009E45: 
           {
             CImplementationClassExtended *classExt = CImplementationClassExtended::NewL();
           aReleaseObject = classExt;
           aBitFlags |= KReleaseRequiredMask; // Indicate release is required
           // Multiple inheritance involved – Cbase and the M class. Must use
               // either dynamic_cast or static_cast to add offset to the base pointer       
           ret = static_cast<MExampleInterfaceExtended2*>(classExt);
           break;
              }                
       }
       return ret;
       }
   

   The plug-in framework releases the extended interface object when the user destroys the instantiation interface object. Alternatively, if the framework wants to release the extended interface earlier, they can call the REComSession::ManuallyReleaseExtendedInterfaceL()

   void CImplementationClass::ReleaseExtendedInterface(TAny* aExtendedInterface, const TUid& aExtendedInterfaceUid)
       {
       switch (aExtendedInterfaceUid.iUid)
       {
       case 0x10009E45:
           {
               // this Extended Interface object require release.
           CImplementationClassExtended* classExt = static_cast<CImplementationClassExtended*>(aReleaseObject);
           delete classExt;
           break;
           }                
       }
       }    
   

   The aInstanceKey parameter is returned by REComSession::CreateImplementationL(). It identifies the instantiation interface object instance. The aExtendedInterfaceUid parameter identifies the extended interface required.
6. 
   Export the instantiation functions into a TImplementationProxy3 table.

   const TImplementationProxy3 KImplementationTable[] =
       {
       IMPLEMENTATION_PROXY_ENTRY3(0x10009E38, CImplementationClass::NewL, CImplementationClass::GetExtendedInterfaceL,CImplementationClass::ReleaseExtenedInterface)
       };
   
   EXPORT_C const TImplementationProxy3* ImplementationGroupProxy(TInt& aTableCount)
       {
       aTableCount = sizeof(KImplementationTable) / sizeof(TImplementationProxy3);
       return KImplementationTable;
       }
   
   

7. 
   Export the release functions into a TImplementationProxy3 table.

   void CImplementationClass::ReleaseExtendedInterface(TAny* aExtendedInterface, const TUid& aExtendedInterfaceUid)
       {
       switch (aExtendedInterfaceUid.iUid)
       {
       case 0x10009E45:
           {
               // this Extended Interface object require release.
           CImplementationClassExtended* classExt = static_cast<CImplementationClassExtended*>(aReleaseObject);
           delete classExt;
           break;
           }                
       }
       }    
   
   

const TUid KExampleInterfaceUid = {0x10009DBB}; // the Instantiation Interface
const TUid KExtendedInterfaceUid1 = {0x10009E44};
const TUid KExtendedInterfaceUid2 = {0x10009E45};

// Set up extended interfaces UID list which form part of the resolution criteria.
RArray<TUid> extendedInterfaces;
CleanupClosePushL(extendedInterfaces);
extendedInterfaces.AppendL(KExtendedInterfaceUid1);
extendedInterfaces.AppendL(KExtendedInterfaceUid2);

// set up resolve parameter
_LIT8(KExampleImplementationData,"Extended Interface Example");
TEComResolverParams ResolverParams;
ResolverParams.SetDataType(KExampleImplementationData());
ResolverParams.SetGenericMatch(ETrue);

TUid instanceKey;
CExampleInterface* instantiateIf = static_cast<CExampleInterface*>(
    REComSession::CreateImplementationL(KExampleInterfaceUid,
                                       extendedInterfaces,
                                       instanceKey,
                                       ResolverParams) );
CleanupStack::PopAndDestroy(&extendedInterfaces);

CleanupStack::PushL(instantiateIf);
// May want to TRAP here if KErrNotSupported is handled, i.e. extension optional
MExampleInterfaceExtended2* ext2 = static_cast<MExampleInterfaceExtended2*>(
  REComSession::GetExtendedInterfaceL(instanceKey, KExtendedInterfaceUid2));

instantiateIf->DoMethodL();  // access old interface function
ext2->DoMethodExtended2();   // access extension function

// Calling ManuallyReleaseExtendedInterface is optional. Do this
// if want to release extended object early.
REComSession::ManuallyReleaseExtendedInterface(instanceKey,KExtendedInterfaceUid2);

REComSession::DestroyedImplementation(instanceKey);
CleanupStack::PopAndDestroy(instantiateIf);