xcode CollectionViewController scrollToItemAtIndexPath not working

Question

I have created a CollectionView Control and filled it with images. Now I want to scroll to item at a particular index on start. I have tried out scrollToItemA

Answer 1

This is based on @Womble's answer, all credit goes to them:

The method viewDidLayoutSubviews() gets called repeatedly. For me (iOS 11.2) the first time it gets called the collectionView.contentSize is {0,0}. The second time, the contentSize is correct. Therefore, I had to add a check for this:

var needsDelayedScrolling = false

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    self.needsDelayedScrolling = true
    // ...
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    if self.needsDelayedScrolling && collectionView.contentSize.width > 0 {
        self.needsDelayedScrolling = false
        self.collectionView!.scrollToItem(at: someIndexPath,
                at: .centeredVertically,
                animated: false)
        }
    }
}

After adding that extra && collectionView.contentSize.width > 0 it works beautifully.