title: custom screen on top of caller screen in android
body: <p>I am trying to launch my custom screen on top of caller screen that may contain fullScreen image of Caller and some buttons for actions like accept or reject call.
  Using this code I can launch my application on top of almost every other application but not over caller screen What's the problem.</p>
  
  <pre><code> Intent mainActivity=new Intent(this,
           PhoneCallActivity.class);
           mainActivity.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP|Intent.FLAG_ACTIVITY_CLEAR_TOP);
           startActivity(mainActivity);
           android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_URGENT_DISPLAY);
  </code></pre>