android: how does facebook messenger interact with my activitity lifecycle?

Issue

I'm trying to learn how to develop Android and I'm currently following this tutorial on the activities lifecycle: https://developer.android.com/training/basics/activity-lifecycle/pausing.html

I created a very simple code to check the triggering of the onPause() and onResume() functions, e.g. for onPause() I just wrote the following in one of my activities (and I did the same kind of stuff for the onResume() function):

@Override
protected void onPause() {
    super.onPause();
    Toast.makeText(this, "ON PAUSE", Toast.LENGTH_LONG).show();
    Log.i("STATUS_ON_PAUSE", "ON PAUSE");
}

When I start/stop the activity or when I switch from one activity to another I do see the corresponding Toasts and logs. But I don't see anything when I overlay a facebook-messenger conversation over my activity. No Toast when opening the conversation (I would have expected to see "ON PAUSE"), no Toast when giving the focus back to my application.

I tried to inspect the log-files on a broader level (my device) but I'm still not good enough to really understand what goes on there (way too much information). So, my question is: how come my activity is not paused/resumed when I give/remove focus to a chat-head? Thanks!

Solution

The simplest answer would be:

Messenger is adding a view to a Window instead of starting a new activity.

This is why Messenger needs SYSTEM_ALERT_WINDOW permission and you can see that when you see it's details: "draw over other apps" permission.

You can see THIS ARTICLE

1. You won't get onPause or onResume when someone is drawing over your window.
2. You will always get onPause and onStop when your activity is covered with other activity.
3. You will always get onPause and no onStop when your activity is covered with a dialog styled activity (so that your activity is still visible in the background).
4. You will not get onPause or onStop when your activity is covered by a DialogFragment - this may look exactly the same as a dialog styled activity but there is a difference in lifecycle and implementation.

Answered By - Mark