code: @Override
      public void onClickConfirmButton() {
          /*
           * Workaround to fix the crash:
  		 * android.view.WindowManager$BadTokenException: Unable to add window
  		 * android.view.ViewRootImpl$W@3d67307 -- permission denied for this window type
  		 * that appears only on Android 6.0 Marshmallow or greater.
  		 * See onActivityResult in this class!!!
  		 */
          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && !Settings.canDrawOverlays(this)) {
              Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                      Uri.parse("package:" + getPackageName()));
              Log.d(TAG, "canDrawOverlay not enabled. Requesting... ");
              startActivityForResult(intent, OVERLAY_PERMISSION_REQ_CODE);
          }
      }
docs: Method defined in
  {@link it.polimi.spf.app.permissiondisclaimer.PermissionDisclaimerDialogFragment.PermissionDisclaimerListener}
  and called by
  {@link it.polimi.spf.app.permissiondisclaimer.PermissionDisclaimerDialogFragment}