There is no global callback for this, but for each activity it is onStop(). You don't need to mess with an atomic int. Just have a global int with the number of started activities, in every activity increment it in onStart() and decrement it in onStop().
public class BaseActivity extends ActionBarActivity {
public static int count = 0;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
protected void onStart() {
super.onStart();
count = count + 1;
Log.d(TAG, "onStart" + count);
if (count == 1) {
Toast.makeText(getApplicationContext(), "online", Toast.LENGTH_SHORT).show();
}
}
protected void onStop() {
super.onStop();
count = count - 1;
if (count == 0) {
Toast.makeText(getApplicationContext(), "offline", Toast.LENGTH_SHORT).show();
}
}
}
