android - Using a broadcast intent/broadcast receiver to send messages from a service to an activity

Question

So I understand (I think) about broadcast intents and receiving messages to them.

So now, my problem/what I can't work out is how to send a message from the onReceive method of a receiver to an activity. Lets say I have a receiver as such:

public class ReceiveMessages extends BroadcastReceiver 
{
@Override
   public void onReceive(Context context, Intent intent) 
   {    
       String action = intent.getAction();
       if(action.equalsIgnoreCase(TheService.DOWNLOADED)){    
           // send message to activity
       }
   }
}

How would I send a message to an activity?

Would I have to instantiate the receiver in the activity I want to send messages to and monitor it somehow? Or what? I understand the concept, but not really the application.

Any help would be absolutely amazing, thank you.

Tom

Answer 1

EDITED Corrected code examples for registering/unregistering the BroadcastReceiver and also removed manifest declaration.

Define ReceiveMessages as an inner class within the Activity which needs to listen for messages from the Service.

Then, declare class variables such as...

ReceiveMessages myReceiver = null;
Boolean myReceiverIsRegistered = false;

In onCreate() use myReceiver = new ReceiveMessages();

Then in onResume()...

if (!myReceiverIsRegistered) {
    registerReceiver(myReceiver, new IntentFilter("com.mycompany.myapp.SOME_MESSAGE"));
    myReceiverIsRegistered = true;
}

...and in onPause()...

if (myReceiverIsRegistered) {
    unregisterReceiver(myReceiver);
    myReceiverIsRegistered = false;
}

In the Service create and broadcast the Intent...

Intent i = new Intent("com.mycompany.myapp.SOME_MESSAGE");
sendBroadcast(i);

And that's about it. Make the 'action' unique to your package / app, i.e., com.mycompany... as in my example. This helps avoiding a situation where other apps or system components might attempt to process it.