self.view.frame changed size ifself unexpectedly in landscape mode

Question

Hi all,

I've setup the view controller's view via IB. The view is set to landscape with width 480 and height 320. It loaded correctly in the simulator. However, when I checked self.frame.size by using NSLog, I found that the frame size changed itself without any rotation of device or any code. Here is what I get:

In viewDidLoad --> size = 480 x 320

In viewWillAppear --> size = 480 x 320

In viewDidAppear --> size = 320 x 480

I only have codes in viewDidLoad, but not viewWillAppear nor viewDidAppear. Anyone knows what happened behind the scene? Thanks.