当使用子类的collectionViewFlowLayout时,我得到了奇怪的错误

Question

我做了一个子类collectionViewFlowLayout.之后,我实现了以下代码:

override func finalLayoutAttributesForDisappearingItemAtIndexPath(itemIndexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
        let attr = self.layoutAttributesForItemAtIndexPath(itemIndexPath)
        attr?.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(0.8, 0.8), CGFloat(M_PI))
        attr?.center = CGPointMake(CGRectGetMidX(self.collectionView!.bounds), CGRectGetMidY(self.collectionView!.bounds))
        return attr
    }

当我使用performBatchUpdates:方法删除集合视图中的项时,调试器会抛出此错误消息.删除实际上成功并且完全正常工作,但我对此调试器输出有点困惑.有人可以解释我应该做什么来取悦调试器吗？我真的不明白什么代码和应该添加到哪里.

//错误信息

2015-08-02 12:39:42.208 nameOfMyProject [1888:51831]仅为UICollectionViewFlowLayout缓存不匹配帧记录一次2015-08-02 12:39:42.209 nameOfMyProject [1888:51831] UICollectionViewFlowLayout缓存了索引路径的帧不匹配{length = 2,path = 0 - 11} - 缓存值:{{106.13333333333333,131.13333333333333},{75.733333333333348,75.733333333333348}}; 预期值:{{192.5,288},{94.666666666666671,94.666666666666671}}

2015-08-02 12:39:42.209 nameOfMyProject [1888:51831]这可能是因为流布局子类nameOfMyProject.ShopLayout正在修改UICollectionViewFlowLayout返回的属性而不复制它们

2015-08-02 12:39:42.209 nameOfMyProject [1888:51831]快照未渲染的视图会导致空快照.确保在屏幕更新后快照或快照之前至少渲染了一次视图.

Answer 1

发生此错误的原因是您在不首先复制属性的情况下操作该属性.所以这应该修复错误:

override func finalLayoutAttributesForDisappearingItemAtIndexPath(itemIndexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
    let attr = self.layoutAttributesForItemAtIndexPath(itemIndexPath)?.copy() as! UICollectionViewLayoutAttributes
    // manipulate the attr
    return attr
}

当您遇到相同的错误时,layoutAttributesForElementsInRect(rect: CGRect)您必须复制数组中的每个项目而不是仅复制数组:

override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let attributes = super.layoutAttributesForElementsInRect(rect)
        var attributesCopy = [UICollectionViewLayoutAttributes]()
        for itemAttributes in attributes! {
            let itemAttributesCopy = itemAttributes.copy() as! UICollectionViewLayoutAttributes
            // manipulate itemAttributesCopy
            attributesCopy.append(itemAttributesCopy)
        }
        return attributesCopy
    }