You can also use (the lazy way)
collectionView.collectionViewLayout.invalidateLayout() // swift
[[_collectionView collectionViewLayout] invalidateLayout] // objc
More complex would be to provide a context
collectionView.collectionViewLayout.invalidateLayout(with: context) // swift
[[_collectionView collectionViewLayout] invalidateLayoutWithContext:context] // objc
You can then make a or configure the context yourself to inform about what should be updated see: UICollectionViewLayoutInvalidationContext
It has a function in there that you can override:
invalidateSupplementaryElements(ofKind:at:) // swift
Another option is (if you have already loaded the correct header/footer/supplementary view) and you only want to update the view with the new data than you can use one of the following functions to retrieve it:
supplementaryView(forElementKind:at:) // get specific one
visibleSupplementaryViews(ofKind:) // all visible ones
Same goes for visible cells with visibleCells. The advantage of just getting the view and not reloading a view entirely is that the cells retains it state. This is espically nice with table view cells when they use swipe to delete/edit/etc since that state is lost after reloading the cell.
If you feel fanatic you can of course also write some extensions to retrieve only cells/supplementary views of a given kind using generics
if let view = supplementaryView(forType: MySupplementaryView.self, at: indexPath) {
configure(view, at indexPath)
}
this assumes that you have a function that registers/dequeues views in example with their class name. I made a post about this here