我创建了以下演示视图控制器,以在一个最小示例中重现该问题。
在这里,我使用 UICollectionViewDiffableDataSource 将相同数据的快照重复应用于相同的集合视图,并且每次重新加载所有单元格时,即使没有任何更改。
我想知道这是否是一个错误,或者我是否“持有错误”。
看起来这个其他用户也有同样的问题,尽管他们没有提供足够的信息来准确地重现错误: iOS UICollectionViewDiffableDataSource reloads all data without changes
编辑:我还发现了一个奇怪的行为 - 如果动画差异是true
,则单元格不会每次都重新加载。
import UIKit
enum Section {
case all
}
struct Item: Hashable {
var name: String = ""
var price: Double = 0.0
init(name: String, price: Double) {
self.name = name
self.price = price
}
}
class ViewController: UIViewController {
private let reuseIdentifier = "ItemCell"
private let collectionView = UICollectionView(frame: .zero, collectionViewLayout: UICollectionViewFlowLayout())
private lazy var dataSource = self.configureDataSource()
private var items: [Item] = [
Item(name: "candle", price: 3.99),
Item(name: "cat", price: 2.99),
Item(name: "dribbble", price: 1.99),
Item(name: "ghost", price: 4.99),
Item(name: "hat", price: 2.99),
Item(name: "owl", price: 5.99),
Item(name: "pot", price: 1.99),
Item(name: "pumkin", price: 0.99),
Item(name: "rip", price: 7.99),
Item(name: "skull", price: 8.99),
Item(name: "sky", price: 0.99),
Item(name: "book", price: 2.99)
]
override func viewDidLoad() {
super.viewDidLoad()
// Configure the collection view:
self.collectionView.backgroundColor = .white
self.collectionView.translatesAutoresizingMaskIntoConstraints = false
self.collectionView.register(ItemCollectionViewCell.self, forCellWithReuseIdentifier: self.reuseIdentifier)
self.collectionView.dataSource = self.dataSource
self.view.addSubview(self.collectionView)
NSLayoutConstraint.activate([
self.collectionView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
self.collectionView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
self.collectionView.topAnchor.constraint(equalTo: self.view.topAnchor),
self.collectionView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
])
// Configure the layout:
let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1/3), heightDimension: .fractionalHeight(1))
let item = NSCollectionLayoutItem(layoutSize: itemSize)
let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalWidth(1/3))
let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
let section = NSCollectionLayoutSection(group: group)
let layout = UICollectionViewCompositionalLayout(section: section)
self.collectionView.setCollectionViewLayout(layout, animated: false)
// Update the snapshot:
self.updateSnapshot()
// Update the snapshot once a second:
Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak self] _ in
self?.updateSnapshot()
}
}
func configureDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
let dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: self.collectionView) { (collectionView, indexPath, item) -> UICollectionViewCell? in
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: self.reuseIdentifier, for: indexPath) as! ItemCollectionViewCell
cell.configure(for: item)
return cell
}
return dataSource
}
func updateSnapshot(animatingChange: Bool = false) {
// Create a snapshot and populate the data
var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
snapshot.appendSections([.all])
snapshot.appendItems(self.items, toSection: .all)
self.dataSource.apply(snapshot, animatingDifferences: false)
}
}
class ItemCollectionViewCell: UICollectionViewCell {
private let nameLabel = UILabel()
private let priceLabel = UILabel()
override init(frame: CGRect) {
super.init(frame: frame)
self.addSubview(self.nameLabel)
self.addSubview(self.priceLabel)
self.translatesAutoresizingMaskIntoConstraints = false
self.nameLabel.translatesAutoresizingMaskIntoConstraints = false
self.nameLabel.textAlignment = .center
self.priceLabel.translatesAutoresizingMaskIntoConstraints = false
self.priceLabel.textAlignment = .center
NSLayoutConstraint.activate([
self.nameLabel.leadingAnchor.constraint(equalTo: self.leadingAnchor),
self.nameLabel.topAnchor.constraint(equalTo: self.topAnchor),
self.nameLabel.trailingAnchor.constraint(equalTo: self.trailingAnchor),
self.priceLabel.topAnchor.constraint(equalTo: self.nameLabel.bottomAnchor),
self.priceLabel.leadingAnchor.constraint(equalTo: self.leadingAnchor),
self.priceLabel.trailingAnchor.constraint(equalTo: self.trailingAnchor),
])
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func configure(for item: Item) {
print("Configuring cell for item \(item)")
self.nameLabel.text = item.name
self.priceLabel.text = "$\(item.price)"
}
}