Gray status bar out UIAlertView style

How can you "gray out" (overlay a gray view w/ alpha ontop of the UIStatusBar) on the iOS exactly like when a UIAlertView displays. I know that it's possible and that Apple allows it since Twitter (official Twitter app) and a fe开发者_Go百科w others implement it. I think you need to add a new window ontop of the current window or a full-screen view

Thanks for your input!

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UIWindow *grayWindow = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
grayWindow.windowLevel = UIWindowLevelStatusBar + 1.0f;
grayWindow.backgroundColor = [UIColor colorWithWhite:0.0f alpha:0.5f];
grayWindow.hidden = NO;