【发布时间】：2021-08-27 06:38:15
【问题描述】：
我实现了一个简单的拖放示例。
import UIKit
class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
private var collectionView: UICollectionView?
var colors: [UIColor] = [
.link,
.systemGreen,
.systemBlue,
.red,
.systemOrange,
.black,
.systemPurple,
.systemYellow,
.systemPink,
.link,
.systemGreen,
.systemBlue,
.red,
.systemOrange,
.black,
.systemPurple,
.systemYellow,
.systemPink
]
override func viewDidLoad() {
super.viewDidLoad()
let layout = UICollectionViewFlowLayout()
layout.scrollDirection = .vertical
layout.itemSize = CGSize(width: view.frame.size.width/3.2, height: view.frame.size.width/3.2)
layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
//collectionView?.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "cell")
let customCollectionViewCellNib = CustomCollectionViewCell.getUINib()
collectionView?.register(customCollectionViewCellNib, forCellWithReuseIdentifier: "cell")
collectionView?.delegate = self
collectionView?.dataSource = self
collectionView?.backgroundColor = .white
view.addSubview(collectionView!)
let gesture = UILongPressGestureRecognizer(target: self, action: #selector(handleLongPressGesture))
collectionView?.addGestureRecognizer(gesture)
}
@objc func handleLongPressGesture(_ gesture: UILongPressGestureRecognizer) {
guard let collectionView = collectionView else {
return
}
switch gesture.state {
case .began:
guard let targetIndexPath = collectionView.indexPathForItem(at: gesture.location(in: self.collectionView)) else {
return
}
collectionView.beginInteractiveMovementForItem(at: targetIndexPath)
case .changed:
collectionView.updateInteractiveMovementTargetPosition(gesture.location(in: collectionView))
case .ended:
collectionView.endInteractiveMovement()
default:
collectionView.cancelInteractiveMovement()
}
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
collectionView?.frame = view.bounds
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return colors.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
cell.backgroundColor = colors[indexPath.row]
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: view.frame.size.width/3.2, height: view.frame.size.width/3.2)
}
func collectionView(_ collectionView: UICollectionView, canMoveItemAt indexPath: IndexPath) -> Bool {
return true
}
func collectionView(_ collectionView: UICollectionView, moveItemAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
let item = colors.remove(at: sourceIndexPath.row)
colors.insert(item, at: destinationIndexPath.row)
}
}
但是，我注意到，如果我的 UICollectionViewCell 是使用 XIB 创建的，它会在拖放过程中随机出现闪烁行为。
CustomCollectionViewCell 是一个非常简单的代码。
CustomCollectionViewCell.swift
import UIKit
extension UIView {
static func instanceFromNib() -> Self {
return getUINib().instantiate(withOwner: self, options: nil)[0] as! Self
}
static func getUINib() -> UINib {
return UINib(nibName: String(describing: self), bundle: nil)
}
}
class CustomCollectionViewCell: UICollectionViewCell {
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
}
}
闪烁
通过使用以下代码
let customCollectionViewCellNib = CustomCollectionViewCell.getUINib()
collectionView?.register(customCollectionViewCellNib, forCellWithReuseIdentifier: "cell")
它将具有以下随机闪烁行为 - https://youtu.be/CbcUAHlRJKI
无闪烁
但是，如果改用下面的代码
collectionView?.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "cell")
一切正常。没有闪烁的行为 - https://youtu.be/QkV2HlIrXK8
我可以知道为什么会这样吗？当我的自定义 UICollectionView 是从 XIB 创建时，如何避免闪烁行为？
请注意，闪烁行为并非一直发生。它随机发生。使用真实的 iPhone 设备比模拟器更容易重现问题。
这是完整的示例代码 - https://github.com/yccheok/xib-view-cell-cause-flickering
【问题讨论】：
标签： ios swift uicollectionview uikit