Android 退出时的监听

[code]private long mLastTime = 0;//退出时间
    /**
     * back键拦截
     */
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            long mSecondTime = System.currentTimeMillis();

            if (mSecondTime - mLastTime > 2000) {// 如果两次按键时间间隔大于2秒，则不退出
                Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
                mLastTime = mSecondTime;// 更新mLastTime
                return true;
            } else {
                MyApplication.getInstance().exit();
                System.exit(0);// 否则退出程序
            }
        }
        return super.onKeyUp(keyCode, event);
    }