show alert in home screen

I would like to make a alertView that can show in any where and don't care there is a View or Window.It just like the safe-model alert can show on the desktop which also can accept user input. The UIAlertView and UIActiveSheet are build upon a UIView or Window.So I didn't need these kinds.I also know the application called b开发者_如何学Cackgrouder has such a alert,but I don't know how to implement it.

You can't. The only way to get your message displayed on the home screen like an SMS is to PUSH this message to the user. Pre condition is that your user has accepted push notifications from your application, and that you're using the Apple Push Notification Service to push info to your users.