android-双击back退出应用

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event)
    {
        if(keyCode == KeyEvent.KEYCODE_BACK){
            quitApp();
            return false;
        }else{
            return super.onKeyDown(keyCode, event);
        }
    }
    /**
     * 退出APP
     */
    private void quitApp(){
        if(isExit){
            Intent intent = new Intent(Intent.ACTION_MAIN);
            intent.addCategory(Intent.CATEGORY_HOME);
            startActivity(intent);
            System.exit(0);
        }else{
            isExit = true;
            Tools.showText(mContext, "再按一次退出应用");
            mHandler.sendEmptyMessageDelayed(0, 2000);
        }
    }
    Handler mHandler = new Handler(){
        public void handleMessage(android.os.Message msg) {
            super.handleMessage(msg);
            isExit = false;
        };
    };

第二种：

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event)
    {
        if(keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0)
            quitApp();
        return false;
    }
    private long exitTime = 0;
    private void quitApp(){
        if(System.currentTimeMillis() - exitTime > 2000){
            Tools.showText(mContext, "再按一次退出应用");
            exitTime = System.currentTimeMillis();
        }else{
            finish();
        }
    }