@Override  public void onBackPressed() {               long currentTime = System.currentTimeMillis();           if((currentTime-touchTime)>=waitTime) {            //让Toast的显示时间和等待时间相同             Toast.makeText(this, "再按一次退出", (int)waitTime).show();               touchTime = currentTime;           }else {               finish();           }    }

long waitTime = 2000;    long touchTime = 0;   @Override  public boolean onKeyDown(int keyCode, KeyEvent event) {      if(event.getAction() == KeyEvent.ACTION_DOWN && KeyEvent.KEYCODE_BACK == keyCode) {            long currentTime = System.currentTimeMillis();            if((currentTime-touchTime)>=waitTime) {                //让Toast的显示时间和等待时间相同              Toast.makeText(this, "再按一次退出", (int)waitTime).show();                touchTime = currentTime;            }else {                finish();            }            return true;        }        return super.onKeyDown(keyCode, event);    }