Type Alias

NSCollectionLayoutSectionVisibleItemsInvalidationHandler

A closure called before each layout cycle to allow modification of items in a section immediately before they are displayed.

Declaration

iOS, Mac Catalyst, tvOS
typealias NSCollectionLayoutSectionVisibleItemsInvalidationHandler = ([NSCollectionLayoutVisibleItem], CGPoint, NSCollectionLayoutEnvironment) -> Void
macOS
typealias NSCollectionLayoutSectionVisibleItemsInvalidationHandler = ([NSCollectionLayoutVisibleItem], NSPoint, NSCollectionLayoutEnvironment) -> Void

Discussion

Each section of a collection view layout can have a visible items invalidation handler. You use this handler to perform custom animations on the items currently visible within the bounds of that section. The handler is called before each layout cycle, any time an animation occurs in that section due to changes such as adding or removing items, scrolling the section, or rotating the device.

let section = NSCollectionLayoutSection(group: group)
    
section.visibleItemsInvalidationHandler = { visibleItems, scrollOffset, layoutEnvironment in
    // perform animations on the visible items
}

See Also

Layout Updates

protocol NSCollectionLayoutVisibleItem

An item that's currently visible within the bounds of a section.

class UICollectionViewUpdateItem

An object that describes a single change to make to an item in a collection view.

class UICollectionViewFocusUpdateContext

A context object that stores information specific to a focus update in a collection view.

class UICollectionViewLayoutInvalidationContext

A context object that declares which parts of your layout need to be updated when the layout is invalidated.