CS0000835 - ECom: Implementing interface

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ID	CS000835	Creation date	February 28, 2008
Platform	S60 3rd Edition, FP1	Tested on devices	Nokia N95
Category	Symbian C++	Subcategory	Base/System

Keywords (APIs, classes, methods, functions): REComSession, TEComResolverParams

Overview

This code snippet demonstrates how to implement an ECom component from the base class.

Preconditions and important issues

The UID2 (0x10009D8D) in the MMP file should be 0x10009D8D, which is common for all ECom plug-ins. The UID3 (0xE01F5465) is the ECom DLL UID.
The UID of this interface can be selected from the protected or unprotected range, depending on the certification path you plan to follow. In this case we are using an unprotected UID so that the application can be self-signed.
If the UID of the plug-in DLL is changed (and, correspondingly, the name of the rss file is changed), the ECom framework may not find the plug-in with the new UID. It may be necessary to delete the ECom.ROM.Z.dat and Ecom.idx files from the development environment folder of the SDK (for example, C:\Symbian\9.1\S60_3rd_MR\Epoc32\winscw\c\private\10009D8F\). When the emulator is restarted, the files are recreated.
The ECom resource name must be identical to the ECom component/DLL name.
Target type (TARGETTYPE) is PLUGIN.
The compiled EComExample.rsc resource file must be copied to the WINSCW environment to \Epoc32\release\winscw\udeb\z\resource\plugins. See the TARGETPATH in the MMP file.

MMP file

TARGET      EComExample.dll
TARGETTYPE  PLUGIN
 
...
 
UID 0x10009D8D 0xE01F5465
 
...
 
SOURCE      Proxy.cpp
SOURCE      CMyHelloEcom.cpp  // Your ECom impl
 
...
 
// Import base class header and inline file
USERINCLUDE     ..\interface 
SYSTEMINCLUDE   \epoc32\include 
SYSTEMINCLUDE   \epoc32\include\ecom
 
// ECom resource name must be identical to ECom component/DLL name. 
START RESOURCE E01F5465.rss
TARGET EComExample.rsc
TARGETPATH \resource\plugins
END

Header file

The header file is derived from the ECom base class.

// Include base class header
#include <CHelloEcomIF.h>
 
class CMyHelloEcom : public CHelloEcomIF
    {
public:
    static CMyHelloEcom* NewL();
    virtual ~CImplementationClassOne();
 
    // Implementation of CHelloEcomIF
    void SayHello(TDes& aString);
 
private:
    CMyHelloEcom();
    void ConstructL();
    };
 
private:
    HBufC* iDescriptor;

Source file

The class must implement the virtual method SayHello(TDes& aString) defined in the base class.

#include "CMyHelloEcom.h"
 
CMyHelloEcom* CMyHelloEcom::NewL()
    {
    CMyHelloEcom* self=new(ELeave) CMyHelloEcom();
    CleanupStack::PushL(self);
    self->ConstructL(); 
    CleanupStack::Pop();
    return self;
    }
 
CMyHelloEcom::~CMyHelloEcom()
    {
    delete iDescriptor;
    }
 
CMyHelloEcom::CMyHelloEcom()
    {
    }
 
void CMyHelloEcom::ConstructL()
    {
    }
 
// Implementation of CHelloEcomIF
void CMyHelloEcom::SayHello(TDes& aString)
    {
    aString.Copy(*iDescriptor);
    }

Plug-in resource file

The resource file describes the contents of your plug-in DLL. It defines IMPLEMENTATION_INFO for individual implementations. IMPLEMENTATION_INFO::implementation_uid is used by ECOM framework's default resolver to find the requested implementation for a client.

#include "RegistryInfo.rh"
 
RESOURCE REGISTRY_INFO theInfo
    {
    // UID for the DLL
    dll_uid = 0xE01F5465;
    // Declare an array of interface info
    interfaces = 
        {
        INTERFACE_INFO
            {
            // UID of the interface that is implemented
            interface_uid = 0xE0009DC1;
            implementations = 
                {
                // Info for implementation of CHelloEcomIF
                IMPLEMENTATION_INFO
                    {
                    implementation_uid = 0xE0009DC7;
                    version_no = 1;
                    display_name = "ecomexample";
                    opaque_data = "";
                    default_data = "ecomexample";
                    }
                };
            }
        };
    }

Proxy

Defines where the implementations reside within the DLL. The ECom framework uses a chart of TImplementationProxy items to map implementation IDs to the locations of specific implementation instantiation methods (NewL). Each implementation ID within TImplementationProxy must match one in the resource file.

#include <e32std.h>
#include <ImplementationProxy.h>
#include "CMyHelloEcom.h"
 
// Maps the interface UIDs to implementation factory functions
const TImplementationProxy ImplementationTable[] = 
    {
    IMPLEMENTATION_PROXY_ENTRY(0xE0009DC7, CMyHelloEcom::NewL)
    };
 
// Exported proxy for instantiation method resolution
EXPORT_C const TImplementationProxy* ImplementationGroupProxy
(TInt& aTableCount)
    {
    aTableCount =
        sizeof(ImplementationTable) / sizeof(TImplementationProxy);
    return ImplementationTable;
    }

Postconditions

The ECom interface has been implemented. The ECom component has a suitable resource file. Implementation factory functions have been defined in the "proxy".

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