android double click to exit app

private var doubleBackToExitPressedOnce = false;

override fun onBackPressed() {
    if (doubleBackToExitPressedOnce) {
        super.onBackPressed()
        return;
    }

    this.doubleBackToExitPressedOnce = true;
    Toast.makeText(this, "Please press BACK again to exit", Toast.LENGTH_SHORT).show();

    Handler(Looper.getMainLooper()).postDelayed(Runnable { doubleBackToExitPressedOnce = false }, 2000);
}