Reloads all of the data for the collection view.
- iOS 6.0+
- tvOS 9.0+
Call this method sparingly when you need to reload all of the items in the collection view. This causes the collection view to discard any currently visible items (including placeholders) and recreate items based on the current state of the data source object. For efficiency, the collection view only displays those cells and supplementary views that are visible. If the collection data shrinks as a result of the reload, the collection view adjusts its scrolling offsets accordingly.
You should not call this method in the middle of animation blocks where items are being inserted or deleted. Insertions and deletions automatically cause the collection’s data to be updated appropriately.