Question

When the app is launched, Application onCreate is called. How to detect when the app is brought to front from running in background?

Answer 1

Look for onResume() method. Its is always called when your app comes foreground.

As per google docs:

The foreground lifetime of an activity happens between a call to
onResume() until a corresponding call to onPause(). During this time
the activity is in front of all other activities and interacting with
the user. An activity can frequently go between the resumed and paused
states — for example when the device goes to sleep, when an activity
result is delivered, when a new intent is delivered — so the code in
these methods should be fairly lightweight.

CODE SAMPLE:

@Override
public void onResume()
{
    super.onResume();
    Log.d("tag", "This screen is back");
}