I currently have a Service in Android that is a sample VOIP client so it listens out for SIP messages and if it recieves one it starts up an Activity screen with UI components.

Then the following SIP messages determine what the Activity is to display on the screen. For example if its an incoming call it will display Answer or Reject or an outgoing call it will show a dialling screen.

At the minute I use Intents to let the Activity know what state it should display.

An example is as follows:

        Intent i = new Intent();
        i.setAction(SIPEngine.SIP_TRYING_INTENT);
        i.putExtra("com.net.INCOMING", true);
        sendBroadcast(i);

        Intent x = new Intent();
        x.setAction(CallManager.SIP_INCOMING_CALL_INTENT);
        sendBroadcast(x);
        Log.d("INTENT SENT", "INTENT SENT INCOMING CALL AFTER PROCESSINVITE");

So the activity will have a broadcast reciever registered for these intents and will switch its state according to the last intent it received.

Sample code as follows:

       SipCallListener = new BroadcastReceiver(){

            @Override
            public void onReceive(Context context, Intent intent) {
                    String action = intent.getAction(); 

                    if(SIPEngine.SIP_RINGING_INTENT.equals(action)){
                        Log.d("cda ", "Got RINGING action SIPENGINE");
                        ringingSetup();
                    }         

                    if(CallManager.SIP_INCOMING_CALL_INTENT.equals(action)){
                        Log.d("cda ", "Got PHONE RINGING action");
                        incomingCallSetup();
                    }  
            }
        };
        IntentFilter filter = new IntentFilter(CallManager.SIP_INCOMING_CALL_INTENT);
        filter.addAction(CallManager.SIP_RINGING_CALL_INTENT);
        registerReceiver(SipCallListener, filter);

This works however it seems like it is not very efficient, the Intents will get broadcast system wide and Intents having to fire for different states seems like it could become inefficient the more I have to include as well as adding complexity.

So I was wondering if there is a different more efficient and cleaner way to do this?

Is there a way to keep Intents broadcasting only inside an application?

Would callbacks be a better idea? If so why and in what way should they be implemented?