CollectionViewUpdater.md

CollectionViewUpdater

CollectionViewUpdater is a class, responsible for animating datasource updates.

Reacting to content updates

Sometimes it's convenient to know, when data is updated, for example to hide UICollectionView, if there's no data. CollectionViewUpdater has willUpdateContent and didUpdateContent properties, that can help:

updater.willUpdateContent = { update in
  print("UI update is about to begin")
}

updater.didUpdateContent = { update in
  print("UI update finished")
}

Please keep in mind, that those closures will not be called if you directly invoke collectionView.reloadData(). If you need to call reloadData and trigger those closures, please call:

manager.collectionViewUpdater?.storageNeedsReloading()

Customizing UICollectionView updates

DTCollectionViewManager uses CollectionViewUpdater class by default. While usually, you don't need to configure anything additional with CollectionViewUpdater, one exception to this rule is CoreData and CoreDataStorage.

When setting up CoreDataStorage with DTTableViewManager and DTCollectionViewManager, consider using special CoreData updater:

manager.collectionViewUpdater = manager.coreDataUpdater()

manager.tableViewUpdater = manager.coreDataUpdater()

This special version of updater has two important differences from default behavior:

1. Moving items is animated as insert and delete
2. When data model changes, update(with:) method and handler closure are called to update visible cells without explicitly reloading them.

Those are recommended by Apple approaches to handle NSFetchedResultsControllerDelegate updates with UITableView and UICollectionView.

If your UICollectionView is not on screen, it's updates are not required to be animated. For performance reasons you may want to disable offscreen animations:

manager.collectionViewUpdater.animateChangesOffScreen = false