Question

I have a strange problem when using a UIScrollView controller combined with iPhone 4 and iOS 5.1.

I have a UIScrollView which has a content size of 640×480 (double screen effectively) and in addition to the swipe to switch between the two “screens” I also permit the user to tap the screen in response to which I call something like…

[scrollView scrollRectToVisible:(CGRectMake 320,0,320,480) animated:YES];

the first 320 would be 0 if the tap occurred whilst the right hand side of the scroll view was displayed (note the scroll view has paging enabled so it can only come to rest either fully left or fully right).

I also have a situation where I sometimes display an additional view controller modally using presentModalViewController over this view controller containing the scroll view.

Everything works perfectly until the modal view controller is presented and subsequently dismissed after which the scrollRectToVisible method will no longer work if animated is set to YES (if I change animated to NO then it works as expected). Note, the tap is still being registered and the scrollRectToVisible being called, it just doesn’t do anything when animated is set to YES).

Here’s the kicker, this bug only occurs on an iPhone 4 runnings iOS 5.x.
It works perfectly (even after the modal view controller has been displayed) on my:
iPhone 3G running 4.x,
iPhone 3GS running 3.x,
iPod touch (2nd Gen) running 4.x
and most surprisingly the simulator running 5.x.

I wondered if this was a bug in the animation system so disabled the animation on the modal view controller presentation and dismiss and this had no effect, problem still occurred on the iPhone 4 with iOS 5.1.

Anyone got any ideas as to what might be causing this and how I might work around it?

Answer 1

I had the same problem. I realized that after modalViewController is dismissed my UIScrollerView shifts downs by 20px, which is the same height as status bar. So, it means when my UIViewController is loaded and UIScrollView is created, UIScrollView thinks there is no status bar, when actually it is there.
So I tried to put in viewDidLoad:

[[UIApplication sharedApplication] setStatusBarHidden:NO];

Now my UIScrollView always stays under status bar, with Y position 20px. It never shifts down.