ios - 动画 UICollectionView 框架时的布局和单元格问题
<p><p><code>UICollectionView</code> 遇到了一个非常奇怪的问题。我不太喜欢一些高级 Collection View 布局的东西，但我仍然认为这有点令人困惑。</p>
<p> <a href="/image/9UAcJ.gif" rel="noreferrer noopener nofollow"><img src="/image/9UAcJ.gif" alt="Collection view animated frame update glitch"/></a> </p>
<p>通过动画应用帧更新(特别是高度变化)使 Collection View (右侧有红色单元格)在将高度设置为较低值时立即刷新即将关闭的单元格。对 <code>UITableView</code> (左侧有黄色单元格)执行相同的更改效果很好。请参阅此 Playground 示例进行演示:</p>
<pre><code>import UIKit
import PlaygroundSupport
class MyViewController : UIViewController, UITableViewDelegate,
UITableViewDataSource, UICollectionViewDelegate, UICollectionViewDataSource
{
var col : UICollectionView?
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 50
}
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
return 50
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let c = UITableViewCell()
c.textLabel?.text = "cell"
c.contentView.backgroundColor = UIColor.yellow
return c
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 50
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let c = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
c.contentView.backgroundColor = UIColor.red
return c
}
func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
// print(Thread.callStackSymbols.joined(separator: "\n") + "\n\n")
}
override func loadView() {
let view = UIView(frame: CGRect(x: 0, y: 0, width: 300, height: 300))
view.backgroundColor = .white
var f = view.bounds
f.size.height = 300
let holder = UIView(frame: view.bounds)
holder.autoresizingMask = [.flexibleWidth]
f.size.width = 150
f.size.height = view.frame.size.height
let table = UITableView(frame: f, style: .plain)
table.delegate = self
table.dataSource = self
table.autoresizingMask = [.flexibleWidth, .flexibleHeight, .flexibleRightMargin]
f.origin.x = 150
let layout = UICollectionViewFlowLayout()
layout.itemSize = CGSize(width: 150, height: 50)
layout.minimumInteritemSpacing = 0
layout.sectionInset = UIEdgeInsets.zero
layout.minimumLineSpacing = 1
let collection = UICollectionView(frame: f, collectionViewLayout: layout)
collection.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "cell")
collection.delegate = self
collection.dataSource = self
collection.autoresizingMask = [.flexibleWidth, .flexibleHeight, .flexibleLeftMargin]
col = collection
view.addSubview(holder)
holder.addSubview(table)
holder.addSubview(collection)
self.view = view
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
toggleContent()
}
func toggleContent()
{
guard let v = self.view.subviews.first else { return }
var f = v.frame
f.size.height = (f.size.height == 300) ? 150:300
UIView.animate(withDuration: 1.0) {
v.frame = f
}
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 1.5) {
self.toggleContent()
}
}
}
PlaygroundPage.current.liveView = MyViewController()
</code></pre>
<p>我希望它首先作为一个魅力发挥作用，因为表格 View 不受此问题的影响。</p>
<p>我已经尝试过使用覆盖流布局并且:</p>
<ul>
<li>设置 <code>shouldInvalidateLayout</code> 方法以返回 <code>false</code>(测试为在单元格即将消失时触发)，以便稍后处理手动失效</li>
<li>扩展 <code>layoutAttributesForElements(in:) 的矩形</code></li>
<li>覆盖 <code>finalLayoutAttributesForDisappearingItem</code></li>
</ul>
<p>没有任何影响。 <code>collectionView(_:didEndDisplaying:)</code> 中注释掉的 <code>print()</code> 显示了 <code>layoutSubviews</code> 无论如何都会调用单元格解除。</p>
<p>动机:这是由此引起的现实问题:</p>
<p> <a href="/image/lInxo.gif" rel="noreferrer noopener nofollow"><img src="/image/lInxo.gif" alt="Real-world problem"/></a> </p>
<p>我想可能有一个非常简单、适当的解决方案？我更喜欢它而不是任何“非常hacky”的东西。</p>
<p>请让我们坚持修复 Playground 示例，不要猜测! ;)</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>尝试通过在动画 block 中添加 <code>layoutIfNeeded()</code> 来更新您的 View ，如下所示:</p>
<pre><code>UIView.animate(withDuration: 1.0) {
v.frame = f
self.view.layoutIfNeeded()
}
</code></pre>
<p>看看它是否有效:/</p></p>
<p style="font-size: 20px;">关于ios - 动画 UICollectionView 框架时的布局和单元格问题，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/51336653/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/51336653/
</a>
</p>
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