If you run the following UIKit app and tap the view controller's right bar button item, the footerText
property will change.
How should I update the collection view's footer to display the updated footerText?
class ViewController: UIViewController {
var collectionView: UICollectionView!
var footerText = "Initial footer text"
var dataSource: UICollectionViewDiffableDataSource<Section, String>!
var snapshot: NSDiffableDataSourceSnapshot<Section, String> {
var snapshot = NSDiffableDataSourceSnapshot<Section, String>()
snapshot.appendSections(Section.allCases)
snapshot.appendItems(["A", "a"], toSection: .first)
return snapshot
}
enum Section: CaseIterable {
case first
}
override func viewDidLoad() {
super.viewDidLoad()
configureHierarchy()
configureDataSource()
}
func configureHierarchy() {
navigationItem.rightBarButtonItem = .init(title: "Change footer text", style: .plain, target: self, action: #selector(changeFooterText))
collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: createLayout())
view.addSubview(collectionView)
collectionView.autoresizingMask = [.flexibleHeight, .flexibleWidth]
}
@objc func changeFooterText() {
footerText = "Secondary footer text"
}
func configureDataSource() {
let cellRegistration = UICollectionView.CellRegistration<UICollectionViewListCell, String> { cell, indexPath, itemIdentifier in
var contentConfiguration = UIListContentConfiguration.cell()
contentConfiguration.text = itemIdentifier
cell.contentConfiguration = contentConfiguration
}
dataSource = .init(collectionView: collectionView) { collectionView, indexPath, itemIdentifier in
collectionView.dequeueConfiguredReusableCell(using: cellRegistration, for: indexPath, item: itemIdentifier)
}
configureSupplementaryViewProvider()
dataSource.apply(self.snapshot)
}
func configureSupplementaryViewProvider() {
let headerRegistration = UICollectionView.SupplementaryRegistration<UICollectionViewListCell>(elementKind: UICollectionView.elementKindSectionHeader) { headerView, elementKind, indexPath in
var contentConfiguration = UIListContentConfiguration.cell()
contentConfiguration.text = "Header \(indexPath.section)"
headerView.contentConfiguration = contentConfiguration
}
let footerRegistration = UICollectionView.SupplementaryRegistration<UICollectionViewListCell>(elementKind: UICollectionView.elementKindSectionFooter) { [weak self] headerView, elementKind, indexPath in
guard let self else { return }
var contentConfiguration = UIListContentConfiguration.cell()
contentConfiguration.text = self.footerText
headerView.contentConfiguration = contentConfiguration
}
dataSource.supplementaryViewProvider = { collectionView, kind, indexPath in
if kind == UICollectionView.elementKindSectionHeader {
collectionView.dequeueConfiguredReusableSupplementary(using: headerRegistration, for: indexPath)
} else if kind == UICollectionView.elementKindSectionFooter {
collectionView.dequeueConfiguredReusableSupplementary(using: footerRegistration, for: indexPath)
} else {
nil
}
}
}
func createLayout() -> UICollectionViewLayout {
UICollectionViewCompositionalLayout { section, layoutEnvironment in
var config = UICollectionLayoutListConfiguration(appearance: .insetGrouped)
config.headerMode = .supplementary
config.footerMode = .supplementary
return NSCollectionLayoutSection.list(using: config, layoutEnvironment: layoutEnvironment)
}
}
}
What I've tried to do in footerText
's didSet:
- Reconfiguring the supplementary view provider:
var footerText = "Initial footer text" {
didSet {
configureSupplementaryViewProvider()
}
}
- Also re-applying the snapshot:
var footerText = "Initial footer text" {
didSet {
configureSupplementaryViewProvider()
dataSource.apply(self.snapshot)
}
}
- Also re-configuring the items:
var footerText = "Initial footer text" {
didSet {
configureSupplementaryViewProvider()
dataSource.apply(self.snapshot, animatingDifferences: true)
var snapshot = dataSource.snapshot()
snapshot.reconfigureItems(snapshot.itemIdentifiers)
dataSource.apply(snapshot, animatingDifferences: false)
}
}
At this time the answer is:
To directly update a supplementaryView
you need to know its kind and section.
With your example, you could add a following didSet
code to a footerText:
var footerText = "Initial footer text" {
didSet {
guard let footer = collectionView.supplementaryView(forElementKind: UICollectionView.elementKindSectionFooter, at: IndexPath(row: 0, section: 0)) as? UICollectionViewListCell else { return }
var contentConfiguration = UIListContentConfiguration.cell()
contentConfiguration.text = self.footerText
footer.contentConfiguration = contentConfiguration
}
}
This way each time you change footerText, your footer will be updated.
You could also move contentConfiguration update to a separate fuction, I've just copied it from your configureSupplementaryViewProvider