Android开发之点击两次Back键退出App

Back按键的方法是onKeyDown()方法，重写该方法就可以改变back按键的作用。

实现点击两次Back按键退出app，有两种方法：

方法1.

    private static boolean isAppExit=false;  //定义一个变量，标示是否退出
    private static Handler mHandler = new Handler() {        
        @Override 
        public void handleMessage(Message msg) { 
            super.handleMessage(msg); 
            isAppExit = false; 
        } 
    };

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {      //重写onKeyDown()方法
        // TODO Auto-generated method stub
        if (keyCode==KeyEvent.KEYCODE_BACK&&event.getRepeatCount()==0) {
            exit();
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

    private void exit() {
        if (!isAppExit) { 
        isAppExit = true; 
        Toast.makeText(getApplicationContext(), "再按一次后退键退出程序", 
                Toast.LENGTH_SHORT).show(); 
        // 利用handler延迟发送更改状态信息 
        mHandler.sendEmptyMessageDelayed(0, 2000); 
        } else {    
        this.finish(); 
        } 
    }

方法2.

    private long clickTime = 0; //记录第一次点击的时间 
    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) { 
        if (keyCode == KeyEvent.KEYCODE_BACK) { 
            exit(); 
            return true; 
        } 
        return super.onKeyDown(keyCode, event); 
    } 
   
    private void exit() { 
        if ((System.currentTimeMillis() - clickTime) > 2000) { 
            Toast.makeText(getApplicationContext(), "再按一次后退键退出程序", 
                    Toast.LENGTH_SHORT).show(); 
            clickTime = System.currentTimeMillis(); 
        } else { 
            Log.e(TAG, "exit application"); 
            this.finish(); 
        } 
    }