How to scroll a UIScrollView on load when using auto layout

Question

I have a UIScrollView that is set up in the viewDidLoad method of a UIViewController (I'll call it a ScrollViewController). The scroll view contains pages of horizontal content (similar to the native weather app).

When displaying the scrollview, it should be possible to choose which page it starts on. My pattern is this:

• init a ScrollViewController. Nothing much happens in here. A currentPage property is defaulted to 0.
• set the scrollViewController.currentPage to the desired page number.
• in viewDidLoad of ScrollViewController, read self.currentPage and use scrollToRect or setContentOffset to scroll accordingly.

The scrolling implementation seems fine, since I am using the same code elsewhere to jump to certain pages. But on first load, nothing happens (that is, the scroll view is not scrolled to the desired page).

I think I have found the reason - it seems that the contentSize of the scroll view (which is derived by autolayout remember) is 0 during viewDidLoad, and this seems that this prevents scrolling. It is also zero during viewWillAppear. Only in viewDidAppear does the scroll work, which of course makes for an odd user experience.

How can I resolve this? Is it wise to somehow force a layout in viewDidLoad? Or some other approach?

Answer 1

viewDidLayoutSubviews is what you are looking for. This is the method where all the subviews frames are completly initialized. So, try to call your scrollView's setup method inside it, in your viewController:

-(void)viewDidLayoutSubviews
{
    [super viewDidLayoutSubviews];
    [self setupView];
}