连续点击两次退出当前程序

//重写onKeyup()，实现连续两次点击方可退出当前程序
private boolean flag = true;
private static final int WHAT_RESET_BACK = 1;
private Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case WHAT_RESET_BACK:
flag = true;//复原
break;
}
}
};
@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
if (keyCode==KeyEvent.KEYCODE_BACK&&flag){
Toast.makeText(MainActivity.this,"再点击一次，退出当前程序",Toast.LENGTH_SHORT).show();
flag = false;
//发送延迟消息
handler.sendEmptyMessageDelayed(WHAT_RESET_BACK,2000);
return true;
}
return super.onKeyUp(keyCode, event);
}

//为了避免内存溢出，需要在onDestroy()中，移除所有未被执行的消息

@Override
protected void onDestroy() {
super.onDestroy();
//方式一：移除指定id的所有消息
//        handler.removeMessages(WHAT_RESET_BACK);
//方式二：移除所有的未被执行的消息
handler.removeCallbacksAndMessages(null);
}