iPhone translucent black UI dialogue: Cocoa Touch or custom?

I've been seeing this type of dialogue appear in different forms in various apps and I'm wondering whether it's a part of Cocoa Touch or a custom jobby. You can see it here, in Tweetie 2.0:

If this is a custom jobby, could anyone offer any pointers as to how to get something like this working? I'm looking to do something similar with开发者_运维技巧 a 'Loading...' message. Cheers guys.

Edit: I've just noticed Apple use a similar control for displaying ringer volume, etc., so I guess it is part of the SDK. Could somebody let me know how/where I could learn more about this?

you can find many of custom UI like this alertview in the Three20 project: here

Check the TTAlertViewController.

Check out MBProgressHUD