我目前有一个 UICollectionView,我正在使用组合布局和 Diffable 数据源。我并没有做任何疯狂的事情,只是将 150 个单元格加载到其中并定义了 4 列布局。每当我点击 collectionview 滚动它似乎正在消失的项目时,我似乎遇到了一些奇怪的行为......下面是我的文件,其中包含我正在使用的整个代码,以便您可以复制并粘贴它并看到这个奇怪的行为。有谁知道为什么会发生这种情况?
import UIKit
class ViewController: UIViewController {
private lazy var myCollectionViewLayout = MyCollectionViewLayout()
override func viewDidLoad() {
super.viewDidLoad()
setup()
// Do any additional setup after loading the view.
}
}
private extension ViewController {
func setup() {
let collectionVw = UICollectionView(frame: .zero, collectionViewLayout: myCollectionViewLayout.createLayout())
collectionVw.translatesAutoresizingMaskIntoConstraints = false
collectionVw.register(MyCustomCell.self, forCellWithReuseIdentifier: MyCustomCell.cellId)
self.view.addSubview(collectionVw)
NSLayoutConstraint.activate([
collectionVw.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor),
collectionVw.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor),
collectionVw.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
collectionVw.trailingAnchor.constraint(equalTo: self.view.trailingAnchor)
])
let dataSource = UICollectionViewDiffableDataSource<Int, UUID>(collectionView: collectionVw) { (collectionView, indexPath, item) -> UICollectionViewCell? in
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MyCustomCell.cellId, for: indexPath) as? MyCustomCell
cell?.configure(at: indexPath.row)
return cell
}
collectionVw.dataSource = dataSource
var snapshot = NSDiffableDataSourceSnapshot<Int, UUID>()
snapshot.appendSections([0])
Range(0...150).forEach { item in
snapshot.appendItems([UUID()], toSection: 0)
}
dataSource.apply(snapshot, animatingDifferences: true)
}
}
class MyCollectionViewLayout {
func createLayout() -> UICollectionViewCompositionalLayout {
let layout = UICollectionViewCompositionalLayout { (sectionIndex: Int, layoutEnv: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.25),
heightDimension: .fractionalHeight(1))
let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1),
heightDimension: .fractionalWidth(0.25))
let item = NSCollectionLayoutItem(layoutSize: itemSize)
let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize,
subitem: item,
count: 4)
group.interItemSpacing = .fixed(16)
let section = NSCollectionLayoutSection(group: group)
section.interGroupSpacing = 16
section.contentInsets = NSDirectionalEdgeInsets(top: 0,
leading: 16,
bottom: 0,
trailing: 16)
return section
}
return layout
}
}
class MyCustomCell: UICollectionViewCell {
static let cellId = "MyCustomCell"
private var lbl: UILabel?
func configure(at index: Int) {
self.contentView.layer.cornerRadius = 8
self.contentView.backgroundColor = .blue
lbl = UILabel()
lbl?.translatesAutoresizingMaskIntoConstraints = false
lbl?.text = index.description
lbl?.textAlignment = .center
lbl?.font = .preferredFont(forTextStyle: .headline)
self.contentView.addSubview(lbl!)
NSLayoutConstraint.activate([
lbl!.topAnchor.constraint(equalTo: self.contentView.topAnchor),
lbl!.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor),
lbl!.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor),
lbl!.trailingAnchor.constraint(equalTo: self.contentView.trailingAnchor)
])
}
override func prepareForReuse() {
super.prepareForReuse()
lbl?.removeFromSuperview()
}
}
最佳答案
原因是您的数据源是您的setup
方法中的局部变量(let dataSource...
)。因此它只工作一次,最初填充 Collection View ,然后消失在一阵烟雾中,留下没有数据的 Collection View 。
数据源必须是 View Controller 的一个属性,这样它才能持久存在!一旦做出改变,一切都会好起来的。
这样做实际上有点棘手,因为数据源取决于 Collection View 。所以你必须使用惰性实例化。您使用空布局创建 Collection View ,并在设置的第一步将所有内容连接在一起。
这是对代码的最小重写;查找我解释更改的评论。
import UIKit
class ViewController: UIViewController {
// delete; this is pointless
// private lazy var myCollectionViewLayout = MyCollectionViewLayout()
override func viewDidLoad() {
super.viewDidLoad()
setup()
}
// need persistent pointer to collection view
let collectionVw = UICollectionView(frame: .zero, collectionViewLayout: UICollectionViewLayout())
// need persistent pointer to data source
lazy var dataSource = UICollectionViewDiffableDataSource<Int, UUID>(collectionView: collectionVw) { (collectionView, indexPath, item) -> UICollectionViewCell? in
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MyCustomCell.cellId, for: indexPath) as? MyCustomCell
cell?.configure(at: indexPath.row)
return cell
}
}
private extension ViewController {
func setup() {
// let collectionVw = UICollectionView(frame: .zero, collectionViewLayout: myCollectionViewLayout.createLayout())
// everything is persistent, now just hook them together
collectionVw.collectionViewLayout = MyCollectionViewLayoutMaker.createLayout()
collectionVw.translatesAutoresizingMaskIntoConstraints = false
collectionVw.register(MyCustomCell.self, forCellWithReuseIdentifier: MyCustomCell.cellId)
self.view.addSubview(collectionVw)
NSLayoutConstraint.activate([
collectionVw.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor),
collectionVw.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor),
collectionVw.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
collectionVw.trailingAnchor.constraint(equalTo: self.view.trailingAnchor)
])
// let dataSource = UICollectionViewDiffableDataSource<Int, UUID>(collectionView: collectionVw) { (collectionView, indexPath, item) -> UICollectionViewCell? in
//
// let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MyCustomCell.cellId, for: indexPath) as? MyCustomCell
// cell?.configure(at: indexPath.row)
// return cell
// }
collectionVw.dataSource = dataSource
var snapshot = NSDiffableDataSourceSnapshot<Int, UUID>()
snapshot.appendSections([0])
Range(0...150).forEach { item in
snapshot.appendItems([UUID()], toSection: 0)
}
dataSource.apply(snapshot, animatingDifferences: true)
}
}
class MyCollectionViewLayoutMaker {
// make this static; the class is not the layout, it serves no purpose except as a factory
static func createLayout() -> UICollectionViewCompositionalLayout {
let layout = UICollectionViewCompositionalLayout { (sectionIndex: Int, layoutEnv: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.25),
heightDimension: .fractionalHeight(1))
let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1),
heightDimension: .fractionalWidth(0.25))
let item = NSCollectionLayoutItem(layoutSize: itemSize)
let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize,
subitem: item,
count: 4)
group.interItemSpacing = .fixed(16)
let section = NSCollectionLayoutSection(group: group)
section.interGroupSpacing = 16
section.contentInsets = NSDirectionalEdgeInsets(top: 0,
leading: 16,
bottom: 0,
trailing: 16)
return section
}
return layout
}
}
class MyCustomCell: UICollectionViewCell {
static let cellId = "MyCustomCell"
private var lbl: UILabel?
func configure(at index: Int) {
self.contentView.layer.cornerRadius = 8
self.contentView.backgroundColor = .blue
lbl = UILabel()
lbl?.translatesAutoresizingMaskIntoConstraints = false
lbl?.text = index.description
lbl?.textAlignment = .center
lbl?.font = .preferredFont(forTextStyle: .headline)
self.contentView.addSubview(lbl!)
NSLayoutConstraint.activate([
lbl!.topAnchor.constraint(equalTo: self.contentView.topAnchor),
lbl!.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor),
lbl!.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor),
lbl!.trailingAnchor.constraint(equalTo: self.contentView.trailingAnchor)
])
}
override func prepareForReuse() {
super.prepareForReuse()
lbl?.removeFromSuperview()
}
}
关于ios - 具有组合布局和差异数据源的 UICollectionView 在滚动时消失,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/62957098/