Draw over other apps on Android 6

AndroidManifest.xml

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

Anywhere.java

public void onClick(View v) {
  Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, 
                              Uri.parse(String.format("package:%s", getPackageName())));
  startActivityForResult(intent, DRAW_OVER_OTHER_APPS);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
  if (requestCode == DRAW_OVER_OTHER_APPS) {
    if (Settings.canDrawOverlays(this)) {
      //Freely draw over other apps
    }
  }
}