点击两次返回键退出程序（简洁）

 

boolean isExit=false;
    Handler mHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            isExit=false;
        }

    };

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub
        if(keyCode == KeyEvent.KEYCODE_BACK){
            if(!isExit){
                isExit=true;
                Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();
                //利用handler延迟发送更改状态信息
                mHandler.sendEmptyMessageDelayed(0, 2000);
            }
            else{
                finish();
                System.exit(0);
            }
        }
        return false;
    }