UICollectionView is a key view type in UIKit and Apple’s Human Interface Guidelines. The Fiori Design Language utilizes collection views in a number of floorplans, especially Object Details, Overview, as well as in the Gallery View, Object CollectionView and Attachments section of the Create View.
The SAPFiori utilizes
UICollectionView instances in a number of controls. When the content for those controls should be managed by the developer, it typically exposes the collection view as a public property in the API. A developer should use the regular UIKit API’s to configure and populate the item views of the collection, and handle things like taps and transitions.
The SAPFiori controls exposing a collection view property include:
These controls implement some context-specific behavior for the collection view–usually around layout and sizing–but when starting to implement a custom collection case, the starting point for a developer should be to work directly with *
Then, the developer can use one or more of the
UICollectionViewLayout types from the SAPFiori framework to govern the item layout, and/or choose from the available
UICollectionViewCell subclasses in the framework to match the design specification.
.horizontalScroll layout extends
UICollectionViewFlowLayout. This layout should be used when the user should pan horizontally in the collection view, to view items off-screen to the left or right. Items in a section extend in a single row to infinity, so items will not wrap to new lines.
A developer should set the
itemSize property of the layout to specify the standard dimensions of the cell items. Alternatively, the developer can implement the
UICollectionViewDelegateFlowLayout to specify unique sizes for each cell item.
A developer may optionally return views to the
collectionView(_:viewForSupplementaryElementOfKind:at:) method, to set ‘supplementary’ views to the collection view’s section header or footer. Multiple sections are supported, though cells in all sections will scroll simultaneously, so single section collections are most common.
Important: this layout ignores the
estimatedItemSizeproperty, even if it is assigned.
.horizontalFlow layout extends
UICollectionViewFlowLayout by adding a new optional property:
minimumScaledItemSize enables the dimensions of the collection view cell items to be scaled upwards, to fill the width of the collection view’s
The developer can allow the layout to scale any number of cell items to fit the
contentSize width, or can set a pre-determined number of items that should fit the
contentSize width by setting the
numberOfColumns property. This is useful when the number of items rendered in the collection view varies on different screens, but a common size is desired.
.horizontalFlow layout also controls the inter-item spacing and line spacing, so that the
minimumLineSpacing values provided by the developer are used precisely, rather than being adjusted by the AutoLayout engine.
With the introduction of this new size property, the
UICollectionViewFlowLayout item size is managed by the following priority:
- Autolayout system, if
estimatedItemSizeis set not equal to
minimumScaledItemSizeis set not equal to
minimumScaledItemSizeis set not equal to
collectionView(_:layout:sizeForItemAt:)value is ignored)
Default flow layout behavior
Flow layout behavior, using
autosizingColumnFlow resizes collection view cell items to lay them out according to a specified number of columns. All items per row are top-aligned, though the cell item height may vary, based upon the AutoLayout system’s height calculation for the cell. The leading/trailing edges of the first and last columns abut the respective margins of the content view.
The developer may specify the number of columns by setting the
Collection view cell items supplied to the
UICollectionViewDataSource.collectionView(_:cellForItemAt:) method for collection views utilizing this flow layout should be well-prepared for the AutoLayout engine to calculate content sizes, especially heights.
keyValueColumnFlow is a variant of the
autosizingColumnFlow, with pre-configured layout characteristics for rendering collections of
- minimumInteritemSpacing is set to 80.
- minimumLineSpacing is set to 24.
- sectionInset is set to UIEdgeInsetsMake(0, 8, 0, 8).