Andriod APP 按兩次返回鍵才確認跳回桌面

[效果]
按一次返回鍵，出現「再按一次返回鍵，退出本APP」提示，
再按一次返回鍵，才跳出APP返回桌面。

[方法]
覆寫 onBackPressed() 方法

......
//連按兩下返回鍵才退出APP
private boolean doubleBackToExitPressedOnce = false;

@Override
public void onBackPressed() {
    if (doubleBackToExitPressedOnce) {
        super.onBackPressed();
        return;
    }
    this.doubleBackToExitPressedOnce = true;
    Snackbar.make(this.getWindow().getDecorView().findViewById(android.R.id.content), "再按一次返回鍵，退出本APP", Snackbar.LENGTH_SHORT).show();
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            doubleBackToExitPressedOnce = false;
        }
    }, 2000);
}
......

參考：

• https://stackoverflow.com/questions/8430805/clicking-the-back-button-twice-to-exit-an-activity?page=2&tab=votes
  java - Clicking the back button twice to exit an activity - Stack Overflow
• https://www.jianshu.com/p/78de93f71965
  最常用的Activity的onBackPressed()与finish()的区别. - 简书