Adding the root view to your UIWindow can be complicated since the window always underlaps the status bar. The frame of your root view must therefore be reset to [[UIScreen mainScreen] applicationFrame] to prevent it from underlapping the status bar as well. We normally don't have to worry about this because UIViewController modifies the frame for us... except when it doesn't. Here's the deal:
- If you create your view controllerand its view in the same NIB, and younest the view underneath the viewcontroller, it will adjust the view's frame automatically.
- If you create your view controller andits view in the same NIB, but youconnect the view to the viewcontroller through the controller'sview outlet rather than nesting it, the controller will not adjust the view's frame automatically.
- If you create your view controller in one NIB, and you connect it to a view defined in a detached NIB by setting the view controller's "NIB Name" property in IB, it will adjust the view's frame automatically, but only if you also have "Resize view from NIB" checked.
- If you create your view controller by calling -initWithNibName:bundle:, it will not adjust the view's frame automatically.
- UITabBarController expects its view to be added as the root view of the window, and therefore always adjusts its own view's frame to match the application frame automatically. (As a result you'll notice a weird 20 pixel gap if you ever add a UITabBarController's view as a subview of anything other than the window.)
I guess Apple figured that -initWithNibName:bundle: wouldn't typically be used to create the window's root view, so it doesn't adjust the frame in your case. Resizing it manually as you have done is fine, and is in fact recommended in the View Controller Programming Guide for iPhone OS, but you should really use [[UIScreen mainScreen] applicationFrame] since the status bar isn't always 20 pixels tall (e.g. it's taller when you're on a phone call.)
解决办法：
CGRect rct = loginController.view.bounds;
rct = [[UIScreen mainScreen] applicationFrame];
[loginController setWantsFullScreenLayout:YES];
rct.origin.y = 20;
loginController.view.frame = rct;
参考链接：
http://stackoverflow.com/questions/2247647/offset-on-uiwindow-addsubview
http://stackoverflow.com/questions/2166718/the-old-display-shifts-down-after-modal-view-controller-issue
