Unity 3D 监听键盘 返回键退出程序C#

 float _waitTime = 2f;//前后两次按退出间隔时间

if (_waitTime < 2)
{
     GUI.Label(new Rect(Screen.width / 2 - 100, Screen.height / 2 - 30, 200, 60), "再按一次退出");
     _waitTime -= Time.deltaTime;
    if (_waitTime < 0)
      {
           _waitTime = 2;
       }
    if (Input.GetKeyDown(KeyCode.Escape))
      {
        Application.Quit();
      }
}
if (Input.GetKeyUp(KeyCode.Escape) && _waitTime == 2)
   {
       _waitTime -= Time.deltaTime;
   }