Where is the proper place to set contentOffset in UIScrollView sub-class? - ios

Question

I am working on a view which inherits from UIScrollView, and the requirement is that it should start at a contentOffset.y position that is dependent on the view size. Specifically I want to start one screen down in a content that is 3 x the view height.
Like this:
- (void)configureStartCondition {
self.contentSize = CGSizeMake(self.bounds.size.width, self.bounds.size.height * 3.0);
self.contentOffset = CGPointMake(0.0, self.bounds.size.height * 1.0);
}
The view itself is wired up with constraints in Storyboard, just like any view. As it works, the framework will initially give the view the size it has in the storyboard, then when the device size is known, the view's size will be changed to its final size. This is how it should work, and I am fine with this. My question is where do I call configureStartCondition?
An obvious solution would be to put this code in setFrame:, but it doesn't work. setFrame: is only called for the initial frame size, which might or might not be the final size. Why is this?
// NOT working
- (void)setFrame:(CGRect)frame {
[super setFrame:frame];
[self configureStartCondition];
}
A more common place would be in layoutSubview, where I usually do this kind of setup. However, as it is a UIScrollView the layoutSubview is called very frequently as the user scrolls the view. Meaning I would need to save the last height and compare it to make things work, then run through this test millions of times just to be able to initialize. It feels like a kludge to me.
// Working, but ugly
- (void)layoutSubview {
[super layoutSubviews];
if (self.bounds.size.height != self.savedHeight) {
self.savedHeight = self.bounds.size.height;
[self configureStartCondition];
}
// Do layout stuff
}
Another place that may seem good is setBounds:. It will get called for the view size change, but since the contentOffset property is tied to the bounds property, I actually get as many calls here as to layoutSubviews.
So, is there a better place to do it, or a better way to do it?
Side issue, less important in my case, but can the content offset be set from a storyboard?
EDIT: Solutions in Swift are also fine.

Answer 1

setContentSize: works perfect for me. It called only when size changed.
PS: My code to check: (sorry for swift but UIKit make no difference)
class CustomScrollView: UIScrollView {
override var contentSize: CGSize{
didSet{
var offset = contentOffset
offset.y = contentSize.height / 2.0
contentOffset = offset
}
}
}