警告：UICollectionViewFlowLayout 的缓存帧与索引路径不匹配 'abc'

Question

这是导致警告的代码：

private override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
    let attributes = super.layoutAttributesForItemAtIndexPath(indexPath)
    let distance = CGRectGetMidX(attributes!.frame) - self.midX;
    var transform = CATransform3DIdentity;
    transform = CATransform3DTranslate(transform, -distance, 0, -self.width);
    attributes!.transform3D = CATransform3DIdentity;
    return attributes
}

控制台还打印：

This is likely occurring because the flow layout "xyz" is modifying attributes returned by UICollectionViewFlowLayout without copying them.

如何修复此警告？

Answer 1

This is likely occurring because the flow layout "xyz" is modifying attributes returned by UICollectionViewFlowLayout without copying them

果然，这正是您正在做的事情：

private override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
    let attributes = super.layoutAttributesForItemAtIndexPath(indexPath)
    let distance = CGRectGetMidX(attributes!.frame) - self.midX;
    var transform = CATransform3DIdentity;
    transform = CATransform3DTranslate(transform, -distance, 0, -self.width);
    attributes!.transform3D = CATransform3DIdentity;
    return attributes
}

我希望你只要说：

let attributes = 
    super.layoutAttributesForItemAtIndexPath(indexPath).copy() 
    as! UICollectionViewLayoutAttributes

或类似的，问题就会消失。

Answer 2

除了上面的好答案。

我知道示例代码是用 swift 编写的，但我认为 Objective-C 版本会有所帮助。

对于Objective-C，这是行不通的，因为复制函数只进行浅拷贝。您必须这样做：

NSArray * original   = [super layoutAttributesForElementsInRect:rect];
NSArray * attributes = [[NSArray alloc] initWithArray:original copyItems:YES];

为了便于阅读，我添加了一个临时变量。

Answer 3

添加到@Georgi 回答

<NSCopying> 必须符合并添加复制消息调用到 layoutAttributesForItemAtIndexPath

UICollectionViewLayoutAttributes* attributes = [[super layoutAttributesForItemAtIndexPath:indexPath] copy];

Answer 4

我在覆盖 layoutAttributesForElementsInRect 时遇到了这个问题。遍历 super.layoutAttributesForElementsInRect(rect) 数组中的每个元素并调用复制对我不起作用，所以我最终回到了基础类并使用 NSArray 的 copyItems：

override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    // unwrap super's attributes
    guard let superArray = super.layoutAttributesForElementsInRect(rect) else { return nil }

    // copy items
    guard let attributes = NSArray(array: superArray, copyItems: true) as? [UICollectionViewLayoutAttributes] else { return nil }

    // modify attributes

    return attributes
}

Answer 5

我已将 UICollectionViewFlowLayout 子类化。在 layoutAttributesForElementsInRect() 里面我做了这个改变：

变化自

guard let attributesForItem: UICollectionViewLayoutAttributes = self.layoutAttributesForItemAtIndexPath(indexPath) else {
    return
}

改为

guard let attributesForItem = self.layoutAttributesForItemAtIndexPath(indexPath)?.copy() as? UICollectionViewLayoutAttributes else {
    return
}

Answer 6

这不是原始问题的答案，但可以帮助 layoutAttributesForElements(in rect: CGRect) (Swift 3.0):

let safeAttributes = super.layoutAttributesForElements(in: rect)?.map { [=10=].copy() as! UICollectionViewLayoutAttributes }
safeAttributes?.forEach { /* do something with attributes*/ }

Answer 7

已更新 Swift 3!

的回复

对于 func layoutAttributesForElements

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {

    guard let attributes = super.layoutAttributesForElements(in: rect) else {
        return nil
    }

    guard let attributesToReturn =  attributes.map( { [=10=].copy() }) as? [UICollectionViewLayoutAttributes] else {
        return nil
    }

    return attributesToReturn

}

对于 func layoutAttributesForItem

override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {

    guard let currentItemAttributes = super.layoutAttributesForItem(at: indexPath)?.copy() as? UICollectionViewLayoutAttributes else {
        return nil
    }

    return currentItemAttributes
}

如果重写这两个函数，则必须在这两个函数上调用复制！

写得不错！

警告：UICollectionViewFlowLayout 的缓存帧与索引路径不匹配 'abc'

Warning: UICollectionViewFlowLayout has cached frame mismatch for index path 'abc'

ios

uicollectionview

uicollectionviewlayout

swift