滚动UICollectionView时如何在顶部屏幕上自定义标题视图？

Question

I have the header (header : UICollectionReusableView ) in my UICollectionView . The header has 3 UIView ( UIView1 , UIView2 , UIView3 ). When I set collectionLayout.sectionHeadersPinToVisibleBounds = true , the header will in top when I scroll the collection. And I want when the header stick in top of UICollectionView , I will hide UIView1 and UIView2 . How can I do that?

Answer 1

UICollectionView is a subclass of UIScrollView . This means that is you assign a delegate to it then this delegate may listen to scrollViewDidScroll(_ scrollView: UIScrollView) method which will be called every time the offset changes in your collection view.

On this event you will need to get all of your header views which I assume you may get by calling visibleSupplementaryViews on your collection view and check its class type.

If the received view is indeed your header you will need to check its frame in comparison to your collection view and see if its position is on top. To do so you may convert frame to your coordinates:

func isHeader(headerView: UIView, onTopOfCollectionView collectionView: UICollectionView) -> Bool {
    guard let collectionSuperView = collectionView.superview else {
         return false // Collection view is not in view hierarchy. This will most likely never happen
    }
    let convertedFrame = headerView.convert(headerView.bounds, to: collectionSuperView) // Convert frame of the view to whatever is the superview of collection view
    return convertedFrame.origin.y <= collectionView.frame.origin.y // Compare frame origins
}

So I guess the whole thing would be something like:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    collectionView.visibleSupplementaryViews(<#My identifier here#>).forEach { view in
        if let header = view as? MyHeaderView {
            header.hideSecondaryViews = isHeader(headerView: header, onTopOfCollectionView: collectionView)
        }
    }
}

I hope this gets you on the right track.