按两次退出

private boolean exit = false;private Handler handler=new Handler(){    @Override    public void handleMessage(Message msg) {        if(msg.what == 1){            exit = false;        }    }};@Overridepublic boolean onKeyUp(int keyCode, KeyEvent event) {    if(event.getKeyCode()==KeyEvent.KEYCODE_BACK)    {        if(!exit){            exit=true;            Toast.makeText(this,"再按一次退出应用",Toast.LENGTH_SHORT).show();            handler.sendEmptyMessageDelayed(1,2000);            return true;        }    }    return super.onKeyUp(keyCode, event);}