Accessing UI thread handler from a service

This snippet of code constructs a Handler associated with the main (UI) thread:

Handler handler = new Handler(Looper.getMainLooper());

You can then post stuff for execution in the main (UI) thread like so:

handler.post(runnable_to_call_from_main_thread);

If the handler itself is created from the main (UI) thread the argument can be omitted for brevity:

Handler handler = new Handler();

The Android Dev Guide on processes and threads has more information.

Create a Messenger object attached to your Handler and pass that Messenger to the Service (e.g., in an Intent extra for startService()). The Service can then send a Message to the Handler via the Messenger. Here is a sample application demonstrating this.

At the moment I prefer using event bus library such as Otto for this kind of problem. Just subscribe the desired components (activity):

protected void onResume() {    super.onResume();    bus.register(this);}

Then provide a callback method:

public void onTimeLeftEvent(TimeLeftEvent ev) {    // process event..}

and then when your service execute a statement like this:

bus.post(new TimeLeftEvent(340));

That POJO will be passed to your above activity and all other subscribing components. Simple and elegant.