Adding custom menu items for a 3rd party MTM

Description:
It is possible to add custom menu items to the Options menu of the Messaging application for a 3rd party MTM message list.

Solution:
To add custom menu items to the message list:
  1) Specify either EMtudContextSpecific or EMtudRemoteOnly flag in the MTM-specific function array.
  2) Use the correct return value in the implementation of CBaseMtmUiData::OperationSupportedL() function.

This function is called by the messaging client to check if a particular operation is appropriate for the selected entries in the message list.
The following example code demonstrates these steps:
1) In UI Data MTM resource file:
    #include ;
    RESOURCE MTUD_FUNCTION r_mymtm_test_operation
        {
        functiontext = "Message command";
        command = ETxtuCommandMessage;
        flags = EMtudContextSpecific|
                EMtudAsynchronous|
                EMtudCommandTransferReceive;
        }
2) Implementation of OperationSupportedL() in the UI Data MTM:
    TInt CTxtiMtmUiData::OperationSupportedL( TInt aOperationId, const TMsvEntry& aContext ) const
      {
      TInt aReasonResourceId=0; // 0 means "operation is available"
      if (aContext.iMtm != KUidMsgTypeText)
        {
        return R_TEXTUD_NOT_SUPPORTED;
        }
    const TBool isMessage = (aContext.iType == KUidMsvMessageEntry);
    const TBool isService = (aContext.iType == KUidMsvServiceEntry);
    if (aOperationId == ETxtuCommandMessage)
        {
        // Only allow this command on local messages
        if ( (!isMessage) | (aContext.iServiceId != KMsvLocalServiceIndexEntryId) )
            aReasonResourceId = R_TEXTUD_ONLY_MESSAGES;
        }
    return aReasonResourceId;
        }