# NSCollectionLayoutBoundarySupplementaryItem An object used to add headers or footers to a collection view. ``` @MainActor class NSCollectionLayoutBoundarySupplementaryItem ``` ## Overview A boundary supplementary item is a specialized type of supplementary item ([`NSCollectionLayoutSupplementaryItem`](/documentation/UIKit/NSCollectionLayoutSupplementaryItem)). You use boundary supplementary items to add headers or footers to a section of a collection view or the entire collection view. Each type of supplementary item must have a unique element kind. Consider tracking these strings together in a way that makes it straightforward to identify each element, for example: ```objc NSString* const ELEMENT_KIND_BADGE = @"badge-element-kind"; NSString* const ELEMENT_KIND_BACKGROUND = @"background-element-kind"; NSString* const ELEMENT_KIND_SECTION_HEADER = @"section-header-element-kind"; NSString* const ELEMENT_KIND_SECTION_FOOTER = @"section-footer-element-kind"; NSString* const ELEMENT_KIND_LAYOUT_HEADER = @"layout-header-element-kind"; NSString* const ELEMENT_KIND_LAYOUT_FOOTER = @"layout-footer-element-kind"; ``` Add boundary supplementary items to a section by setting that section’s [`boundarySupplementaryItems`](/documentation/UIKit/NSCollectionLayoutSection/boundarySupplementaryItems) property: ```objc NSCollectionLayoutSection *section = [NSCollectionLayoutSection sectionWithGroup:group]; NSCollectionLayoutSize *headerFooterSize = [NSCollectionLayoutSize sizeWithWidthDimension:[NSCollectionLayoutDimension fractionalWidthDimension:1.0] heightDimension:[NSCollectionLayoutDimension absoluteDimension:44.0]]; NSCollectionLayoutBoundarySupplementaryItem *sectionHeader = [NSCollectionLayoutBoundarySupplementaryItem boundarySupplementaryItemWithLayoutSize: headerFooterSize elementKind: ELEMENT_KIND_SECTION_HEADER alignment: NSRectAlignmentTop]; NSCollectionLayoutBoundarySupplementaryItem *sectionFooter = [NSCollectionLayoutBoundarySupplementaryItem boundarySupplementaryItemWithLayoutSize: headerFooterSize elementKind: ELEMENT_KIND_SECTION_FOOTER alignment: NSRectAlignmentBottom]; [section setBoundarySupplementaryItems: @[sectionHeader, sectionFooter]]; ``` ## Topics ### Creating a boundary supplementary item [`init(layoutSize:elementKind:alignment:)`](/documentation/UIKit/NSCollectionLayoutBoundarySupplementaryItem/init(layoutSize:elementKind:alignment:)) Creates a boundary supplementary item of the specified size and element kind, with an alignment relative to a section or layout. [`init(layoutSize:elementKind:alignment:absoluteOffset:)`](/documentation/UIKit/NSCollectionLayoutBoundarySupplementaryItem/init(layoutSize:elementKind:alignment:absoluteOffset:)) Creates a boundary supplementary item of the specified size and element kind, with an alignment relative to a section or layout at an absolute offset. ### Specifying scrolling behavior [`pinToVisibleBounds`](/documentation/UIKit/NSCollectionLayoutBoundarySupplementaryItem/pinToVisibleBounds) A Boolean value that indicates whether a header or footer is pinned to the top or bottom visible boundary of the section or layout it’s attached to. ### Specifying position [`offset`](/documentation/UIKit/NSCollectionLayoutBoundarySupplementaryItem/offset) The floating-point value of the boundary supplementary item’s offset from the section or layout it’s attached to. [`alignment`](/documentation/UIKit/NSCollectionLayoutBoundarySupplementaryItem/alignment) The alignment of the boundary supplementary item relative to the section or layout it’s attached to. [`extendsBoundary`](/documentation/UIKit/NSCollectionLayoutBoundarySupplementaryItem/extendsBoundary) A Boolean value that indicates whether a boundary supplementary item extends the content area of the section or layout it’s attached to. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)