Question

我有一个水平滚动UICollectionView，它位于垂直滚动UICollectionView的单元格内。当垂直滚动collectionView滚动时，其内部的水平滚动collectionView会根据它在垂直集合视图中呈现单元格的位置来调整大小。

collectionViews概要：

layout:                   scrolling:
______________________    ______________________
|         ^          |    | while   ^          |
|         | Vertical |    |   this  | scrolls: |
| __________________ |    | __________________ |
| |                | |    | |       ^        | |
| |                | |    | |       |        | |
| |<- Horizontal ->| |    | |<- This Grows ->| |
| |                | |    | |________________| |
| |________________| |    |____________________|
|____________________|    |   ______________   |
                          |   |     ^      |   |
                          |   |     |      |   |
                          |   |<-  grows ->|   |
                          |   |____________|   |
                          |____________________|

要在滚动时更改大小，我会为更新框架的内部collectionView更新宽度NSLayoutConstraint（collectionView有其他约束以保持其纵横比和位置正确）：

for (constraint, definition) in parralaxDict {
    // calculates offset for each constraint
    constraint.constant = definition.parralaxOffset(forPosition: position, inRect: bounds)
}
layoutIfNeeded()

这很棒，但是我得到了关于流程布局的 TON 错误的itemSize：

the behavior of the UICollectionViewFlowLayout is not defined because: 
the item height must be less than the height of the UICollectionView minus the section insets top and bottom values.

没问题，我想。如果需要，我会在调用布局之前使布局无效：

for (constraint, definition) in parralaxDict {
    // calculates offset for each constraint
    constraint.constant = definition.parralaxOffset(forPosition: position, inRect: bounds)
}
// layout.invalidateLayout() // tried here, nope
layoutIfNeeded()
// layout.invalidateLayout() // tried here, double nope

由于这不起作用，我尝试将流程布局shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool设置为true。这做了两件事：

仅对FULL更改触发（即当CGFloat命中1.0,2.0,3.0但不是1.1112,1.1345等时触发。）
没有解决问题。

我还尝试在更新约束时无法直接设置itemSize。

值得注意的是，我做了UICollectionViewFlowLayout的子类，如下所示：

class PhotoCollectionViewFlowLayout: UICollectionViewFlowLayout {

    class func layout() -> PhotoCollectionViewFlowLayout {
        let layout = PhotoCollectionViewFlowLayout()
        layout.setup()
        return layout
    }

    private func setup() {
        scrollDirection = .Horizontal
        minimumInteritemSpacing = 0.0
        minimumLineSpacing = 0.0
        sectionInset = UIEdgeInsetsZero
    }

    override func prepareLayout() {
        super.prepareLayout()

        if let theCollectionView = collectionView {
            var newItemSize = itemSize
            newItemSize.width = theCollectionView.bounds.size.width - (sectionInset.left + sectionInset.right)
            newItemSize.height = theCollectionView.bounds.size.height - (sectionInset.top + sectionInset.bottom)
            itemSize = newItemSize
        }
    }   
}

有什么想法我可以做些什么来消除这些错误？

通过修改约束来调整大小时的UICollectionView itemSize问题

0 个答案: