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ios - UICollectionViewDiffableDataSource 正在替换数据而不是更新

转载 作者:行者123 更新时间:2023-12-05 06:13:44 25 4
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我正在尝试理解 UICollectionViewDiffableDataSourceNSDiffableDataSourceSnapshot

我在下面创建了一个非常粗糙的版本。基本上在加载时它应该获取照片。

点击导航栏中的按钮,它会获取下一页。然而,这只是替换现有数据,我期望它将值附加到数组。

我应该如何更新我的数据而不是替换它?

class ViewController: UIViewController {

lazy var collectionView = UICollectionView(frame: view.frame, collectionViewLayout: UICollectionViewFlowLayout())

enum Section {
case main
}

typealias DataSource = UICollectionViewDiffableDataSource<Section, AnyHashable>
typealias DataSourceSnapshot = NSDiffableDataSourceSnapshot<Section, AnyHashable>

private var dataSource: DataSource!
private var snapshot = DataSourceSnapshot()

override func viewDidLoad() {
super.viewDidLoad()

let updateButton = UIBarButtonItem(title: "Add", style: .plain, target: self, action: #selector(onTapLoad))
navigationItem.rightBarButtonItem = updateButton

view.addSubview(collectionView)
collectionView.autoresizingMask = [.flexibleHeight, .flexibleWidth]
collectionView.delegate = self
collectionView.backgroundColor = .systemBackground
collectionView.register(PhotoCell.self, forCellWithReuseIdentifier: "PhotoCell")

dataSource = DataSource(collectionView: collectionView, cellProvider: { (cv, indexPath, object) -> PhotoCell? in

if let object = object as? Photo {
let cell = cv.dequeueReusableCell(withReuseIdentifier: "PhotoCell", for: indexPath) as! PhotoCell
cell.backgroundColor = indexPath.item % 2 == 0 ? .systemTeal : .systemPink
cell.label.text = object.title
return cell
}

return nil
})

load()
}

@objc func onTapLoad() {
load(page: 1)
}

func load(page: Int = 0) {
PhotoLoader.shared.load(page: page) { result in
if let photos = try? result.get() {
self.apply(photos)
}
}
}

func apply(_ photos: [Photo]) {

snapshot = DataSourceSnapshot()
snapshot.appendSections([Section.main])
snapshot.appendItems(photos)

dataSource.apply(snapshot, animatingDifferences: false)
}
}

extension ViewController: UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return .init(width: collectionView.frame.width - 32, height: 100)
}
}

struct Photo: Decodable, Hashable {
let id = UUID()
let title: String
}

final class PhotoLoader {

static let shared = PhotoLoader()

func load(page: Int, completion: @escaping (Result<[Photo], Error>) -> Void) {

URLSession.shared.dataTask(with: URL(string: "https://jsonplaceholder.typicode.com/photos?_start=\(page)&_limit=5")!, completionHandler: { data, response, error in
if let data = data, let model = try? JSONDecoder().decode([Photo].self, from: data) {
completion(.success(model))
}
}).resume()
}
}

final class PhotoCell: UICollectionViewCell {
lazy var label = UILabel(frame: .zero)

override init(frame: CGRect) {
super.init(frame: frame)

label.translatesAutoresizingMaskIntoConstraints = false
label.numberOfLines = 3
addSubview(label)
NSLayoutConstraint.activate([
label.topAnchor.constraint(equalTo: topAnchor),
label.leadingAnchor.constraint(equalTo: leadingAnchor),
label.bottomAnchor.constraint(equalTo: bottomAnchor),
label.trailingAnchor.constraint(equalTo: trailingAnchor)
])

}

required init?(coder: NSCoder) {
return nil
}

}

最佳答案

在不使用额外数组的情况下初始化 viewDidLoad 中的快照

override func viewDidLoad() {
super.viewDidLoad()

...
let snapshot = DataSourceSnapshot()
snapshot.appendSections([Section.main])
dataSource.apply(snapshot, animatingDifferences: false)
}

并在apply(_ photos)将照片附加到当前快照而不是创建新快照

func apply(_ photos: [Photo]) {

var snapshot = dataSource.snapshot()
snapshot.appendItems(photos, toSection: .main)
dataSource.apply(snapshot, animatingDifferences: true)
}

不需要该属性

<罢工> 私有(private) var 快照 = DataSourceSnapshot()

注意:

尽可能具体地声明数据源

typealias DataSource = UICollectionViewDiffableDataSource<Section, Photo>
typealias DataSourceSnapshot = NSDiffableDataSourceSnapshot<Section, Photo>

然后你就摆脱了不必要的类型检查

dataSource = DataSource(collectionView: collectionView, cellProvider: { (cv, indexPath, photo) -> PhotoCell? in

let cell = cv.dequeueReusableCell(withReuseIdentifier: "PhotoCell", for: indexPath) as! PhotoCell
cell.backgroundColor = indexPath.item % 2 == 0 ? .systemTeal : .systemPink
cell.label.text = photo.title
return cell

})

关于ios - UICollectionViewDiffableDataSource 正在替换数据而不是更新,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/63162333/

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