Insert, Delete, Move and Reload

As data changes a collection view displaying that data will need to update as well. New content could be pulled from a remote service or the user could take an action. Collection view supports inserting, deleting, moving, and reloading sections and items.

Single Updates

To perform a single update operation you can use any of the update functions directly.

public func insertSections(_ sections: IndexSet, animated: Bool)
public func deleteSections(_ sections: IndexSet, animated: Bool)
public func moveSection(_ section: Int, to newSection: Int, animated: Bool)

public func insertItems(at indexPaths: [IndexPath], animated: Bool)
public func deleteItems(at indexPaths: [IndexPath], animated: Bool)
public func reloadItems(at indexPaths: [IndexPath], animated: Bool)
public func moveItem(at indexPath : IndexPath, to destinationIndexPath: IndexPath, animated: Bool)

Before doing so you must be sure that your data source will report the change. For example, if inserting an item your data source must report 1 more item than the collection view currently has.

Note that these operations currently reload the entire layout object and should not be called excessivly.

Batch Updates

Multiple updates can be performed simultaneously use performBatchUpdates(_:completion:). Any changes made in the first closure will be batched together and commited as a single operation.

myData.remove(at: 1)
myData.append("Another Entry")

collectionView.performBatchUpdates({
    collectionView.deletItems(at: [IndexPath.for(item: 1, section: 0)])
    collectionView.insertITems(at: [[IndexPath.for(item: myData.count - 1, section: 0)]])
}) { (completed) in
    // Animation is complete!
}

Note that delete and reload updates use index paths prior to any changes, inserts refer to index paths after all changes are made, and moves go from a pre-update index path fo a post-updates index path. The following illustrates this

Section A
[H] [J] [K]
Section B
[X] [Y] [Z]

move section A to 1
Move [1, 1] to [1, 1]

Section B
[X] [Z]
Section A
[H] [Y] [J] [K]

Notice that the second move at [1, 1] moves [Y] from its starting index path [1, 1] to its final index path after changes [1, 1].

Managing these changes can be tricky to understand especially when making many changes together. This is why we create ResultsController to help connect your collection view to your data.