10.3 - Receiving Interface Messages

Messages are received by registering callback functions for the interface message content types of interest.

Objects can register a callback to be fired upon receipt of a given kind of interface message through the DtVrfMessageInterface. Message callback functions are specified as:

static void messageCallback(DtSimMessage * msg, void * usrData);

The callback receives a pointer to a DtSimMessage (simMsg.h), which is the base class from which DtSimInterfaceMessage is derived. (This is because the radio message callback mechanism use the same kind of callback - but with a different derived type of DtSimMessage, a DtVrfObjectMessage (vrfObjectMessage.h).) The message received can be cast to a DtSimInterfaceMessage so that its contents can be retrieved. A callback must not delete the messages it receives. The specification for the DtVrfMessageInterface member function for adding a callback is:

virtual void addMessageCallback(int type, DtMessageCallbackFcn fcn, 
void* usrData);

where:

• type is the interface message type (message types are in msgTypes.h)
• fcn is a callback as specified above
• usrData is a pointer to the data that will be passed to the callback.

The following example shows a callback being registered for a DtIfDeleteVrfObject with an instance of a DtSimManager pointed to by mySimManager. It provides its "this" pointer as usrData.

mySimManager->messageInterface()->addMessageCallback(
DtIfDeleteVrfObjectType, MyClass::deleteObjectCallback, this);

void deleteObjectCallback(DtSimMessage* msg, void * usrData)
{
   // We know the type of DtSimMesssage is a DtSimInterfaceMessage.
   DtSimInterfaceMessage * ifMsg = (DtSimInterfaceMessage *) msg;

   // We know that the content of the incoming message will be of type 
   // DtIfDeleteVrfObject.
   DtIfDeleteVrfObject * deleteVrfObjectInfo =    
      (DtIfDeleteVrfObject*)ifMsg->interfaceContent();

   DtInfo("Received delete object message for object %s\n",
      deleteVrfObjectInfo->markingText().string());
}

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