【Android Demo】点击两次Back键退出当前程序

package com.yc.toquitapp;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.KeyEvent;
import android.widget.Toast;

public class MainActivity extends Activity {

    private boolean isExit = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // ClickTwiceBackToQuit

    }

    // 重写Activity中onKeyDown（）方法
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {// 当keyCode等于退出事件值时
            ToQuitTheApp();
            return false;
        } else {
            return super.onKeyDown(keyCode, event);
        }
    }

    //封装ToQuitTheApp方法
    private void ToQuitTheApp() {
        if (isExit) {
            // ACTION_MAIN with category CATEGORY_HOME 启动主屏幕
            Intent intent = new Intent(Intent.ACTION_MAIN);
            intent.addCategory(Intent.CATEGORY_HOME);
            startActivity(intent);
            System.exit(0);// 使虚拟机停止运行并退出程序
        } else {
            isExit = true;
            Toast.makeText(MainActivity.this, "再按一次退出APP", Toast.LENGTH_SHORT).show();
            mHandler.sendEmptyMessageDelayed(0, 3000);// 3秒后发送消息
        }
    }

    //创建Handler对象，用来处理消息
    Handler mHandler = new Handler() {

        @Override
        public void handleMessage(Message msg) {//处理消息
            // TODO Auto-generated method stub
            super.handleMessage(msg);
            isExit = false;
        }
    };
}