集合视图的自定义布局不更新

Posted 2023-03-11

【中文标题】集合视图的自定义布局不更新

【英文标题】：Custom Layout for Collection view doesn't update

【发布时间】：2018-10-23 10:49:26

【问题描述】：

我正在使用以下代码来为各种单元格设置高度可变的UICollectionView：

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int 
        return totalItems
    

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) 

        totalItems -= 1

        collectionView.deleteItems(at: [indexPath])
        collectionView.collectionViewLayout.invalidateLayout()
    


extension InviteViewController : PinterestLayoutDelegate 

    // 1. Returns the cell height
    func collectionView(_ collectionView: UICollectionView, heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat 
        print("have: ", indexPath.item)
        if(indexPath.item % 3 == 0) 
            return 150
         else if(indexPath.item % 3 == 1) 
            return 200
         else 
            return 250
        
    

但是我看到删除 UICollectionViewCell 后布局没有更新，并且出现以下错误：

*** 由于未捕获的异常“NSInternalInconsistencyException”而终止应用程序，原因：“UICollectionView 接收到具有不存在索引路径的单元格的布局属性：length = 2, path = 0 - 7”

我被卡住了，无法理解为什么会发生这种情况以及如何解决这个问题。请帮我找到相同的解决方案。谢谢。

如果你想看看我使用的布局文件，请看这里：

import UIKit

protocol PinterestLayoutDelegate: class 
    // 1. Method to ask the delegate for the height of the image
    func collectionView(_ collectionView:UICollectionView, heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat


class PinterestLayout: UICollectionViewLayout 
    //1. Pinterest Layout Delegate
    weak var delegate: PinterestLayoutDelegate!

    //2. Configurable properties
    fileprivate var numberOfColumns = 2
    fileprivate var cellPadding: CGFloat = 3

    //3. Array to keep a cache of attributes.
    fileprivate var cache = [UICollectionViewLayoutAttributes]()

    //4. Content height and size
    fileprivate var contentHeight: CGFloat = 0

    fileprivate var contentWidth: CGFloat 
        guard let collectionView = collectionView else 
            return 0
        
        let insets = collectionView.contentInset
        return collectionView.bounds.width - (insets.left + insets.right)
    

    override var collectionViewContentSize: CGSize 
        return CGSize(width: contentWidth, height: contentHeight)
    

    override func prepare() 
        // 1. Only calculate once
        guard cache.isEmpty == true, let collectionView = collectionView else 
            return
        
        // 2. Pre-Calculates the X Offset for every column and adds an array to increment the currently max Y Offset for each column
        let columnWidth = contentWidth / CGFloat(numberOfColumns)
        var xOffset = [CGFloat]()
        for column in 0 ..< numberOfColumns 
            xOffset.append(CGFloat(column) * columnWidth)
        
        var column = 0
        var yOffset = [CGFloat](repeating: 0, count: numberOfColumns)

        // 3. Iterates through the list of items in the first section
        for item in 0 ..< collectionView.numberOfItems(inSection: 0) 

            let indexPath = IndexPath(item: item, section: 0)

            // 4. Asks the delegate for the height of the picture and the annotation and calculates the cell frame.
            let photoHeight = delegate.collectionView(collectionView, heightForPhotoAtIndexPath: indexPath)
            let height = cellPadding * 2 + photoHeight
            let frame = CGRect(x: xOffset[column], y: yOffset[column], width: columnWidth, height: height)
            let insetFrame = frame.insetBy(dx: cellPadding, dy: cellPadding)

            // 5. Creates an UICollectionViewLayoutItem with the frame and add it to the cache
            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            attributes.frame = insetFrame
            cache.append(attributes)

            // 6. Updates the collection view content height
            contentHeight = max(contentHeight, frame.maxY)
            yOffset[column] = yOffset[column] + height

            column = column < (numberOfColumns - 1) ? (column + 1) : 0
        
    

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

        var visibleLayoutAttributes = [UICollectionViewLayoutAttributes]()

        // Loop through the cache and look for items in the rect
        for attributes in cache 
            if attributes.frame.intersects(rect) 
                visibleLayoutAttributes.append(attributes)
            
        
        return visibleLayoutAttributes
    

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? 
        return cache[indexPath.item]
    

我关注了：https://www.raywenderlich.com/392-uicollectionview-custom-layout-tutorial-pinterest

【参考方案1】：

override func prepare() 
    // 1. Only calculate once
    guard cache.isEmpty == true, let collectionView = collectionView else 
        return
    

在这部分删除guard cache.isEmpty == true,。它有效。

extension CategoryPageVC: PinterestLayoutDelegate 
    func collectionView(_ collectionView: UICollectionView,
                        heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat 

let rate = self.categoryData[indexPath.item].image.size.width / self.collectionView.frame.size.width * 2
        return self.categoryData[indexPath.item].image.size.height / rate
    

【讨论】：

谢谢，但集合视图单元格的高度仍然不正确。即使所有单元格都被删除，它也将具有与开始时相同的可滚动高度。在这种情况下该怎么办？ @codeByThey