Crash in CollectionView For Invalid Header - ios

Question

I want to understand what this error means?
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason:
'the view returned from -collectionView:viewForSupplementaryElementOfKind:atIndexPath: was not
retrieved by calling -dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
for element kind 'UICollectionElementKindSectionHeader' at index path <NSIndexPath: 0x8aeb905cf5be0ed2>
{length = 2, path = 0 - 0}; supplementary view:
<UICollectionReusableView: 0x7f9236dc4ff0; frame = (0 0; 0 0); layer = <CALayer: 0x600001018620>>'
I am using custom header for UICollectionView.I am getting this crash as soon as the view is loaded. even before cellforrowatindexpath is called and the issue is not with the custom header, it is with the return UICollectionReusableView()
func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
if kind == UICollectionView.elementKindSectionHeader && indexPath.section == 2
{
return someCustomHeader
}
return UICollectionReusableView()
}

Answer 1

You must always obtain the section header with the method dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:, before calling it you must also register a header class. If you want to show only the header of the third section you must implement collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) to hide unwanted headers by giving them a .zero size (you can' t simply return an instance of UICollectionReusableView for unwanted headers).
import UIKit
class CollectionViewController: UICollectionViewController {
private let headerId = "headerId"
override func viewDidLoad(){
super.viewDidLoad()
// Registers a header class
self.collectionView.register(YourClass.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: self.headerId) // Replace YourClass with the name of your header class
}
func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
// This method must always call dequeueReusableSupplementaryView, even if section!=2
if kind == UICollectionView.elementKindSectionHeader{
return self.collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: self.headerId, for: indexPath)
}
return UICollectionReusableView()
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize{
// Shows only the header of the third section
return section == 2 ? desiredSize : .zero // Replace desiredSize with the size of the visible header
}
}

Answer 2

When you work with custom header you have to register first the header class.
collectionView.register(AppHeaderCollectionView.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: AppHeaderCollectionView.headerIdentifier)
and after that for use the header you have to do it this.
override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: AppHeaderCollectionView.headerIdentifier, for: indexPath) as! AppHeaderCollectionView
return header
}

Answer 3

After the iOS update to 15.0, I had to subclass UICollectionReusableView for my header view.
guard let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: MenuTitleHeaderView.sectionHeaderID, for: indexPath) as? MenuTitleHeaderView else {
fatalError("Unexpected Sumplementary View")
}
switch kind {
case UICollectionView.elementKindSectionHeader:
...
}
Don't forget to return the size for the header or footer as well.
One more thing, don't forget to return the number of sections. Or you will only see one section display.