ios - 消除 UICollectionView 单元格之间的间隙

Question

我正在尝试制作具有自由高度的灵活collectionview。但我无法垂直消除单元格之间的额外间隙。

    collectionView = UICollectionView(frame: .zero, collectionViewLayout: UICollectionViewFlowLayout())
    collectionView.register(MultilineLabelCell.self, forCellWithReuseIdentifier: MultilineLabelCell.reuseId)
    view.addSubview(collectionView)
    collectionView.backgroundColor = .white
    collectionView.contentInsetAdjustmentBehavior = .always
    collectionView.contentInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
    collectionView.frame = self.view.bounds
    collectionView.dataSource = self
    collectionView.delegate = self
    (collectionView.collectionViewLayout as! UICollectionViewFlowLayout).estimatedItemSize = UICollectionViewFlowLayout.automaticSize


func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MultilineLabelCell.reuseId, for: indexPath) as! MultilineLabelCell
    cell.configure(note: viewModel.notes![indexPath.row])
    return cell
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return viewModel.notes!.count
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let referenceHeight: CGFloat = 100 // Approximate height of cell
    let referenceWidth = collectionView.safeAreaLayoutGuide.layoutFrame.width/2.2
    return CGSize(width: referenceWidth, height: referenceHeight)
}

标签： iosswiftuicollectionview

Answer 1

你可以像这样得到一个 UICollectionView。

为此，我在我的应用程序中为自定义 UICollectionViewLayout 使用以下代码（我没有更改它，但方法本身很容易理解）

import UIKit

protocol StoryAppCollectionLayoutDelegate: AnyObject {
  func collectionView(_ collectionView: UICollectionView, heightForPhotoAtIndexPath indexPath: IndexPath) -> CGFloat
}

class StoryAppCollectionLayout: UICollectionViewLayout {

weak var delegate: StoryAppCollectionLayoutDelegate?
private var numberOfColumns = 2
private let cellPadding: CGFloat = 6
private var cache: [UICollectionViewLayoutAttributes] = []
private var contentHeight: CGFloat = 0
private var previousBounds: CGRect?
private var previousNumberOfColumns : Int?

private 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() {
    if let collectionView = collectionView {

        numberOfColumns = Int(collectionView.bounds.width / CARD_ITEM_SIZE)
        if previousNumberOfColumns == numberOfColumns {
            return
        }
        previousNumberOfColumns = numberOfColumns
        
        cache.removeAll()
        
        let columnWidth = CARD_ITEM_SIZE // contentWidth / CGFloat(numberOfColumns)
        var xOffset: [CGFloat] = []
        for column in 0 ..< numberOfColumns {
            xOffset.append(CGFloat(column) * columnWidth)
        }
        var column = 0
        var yOffset: [CGFloat] = .init(repeating: 0, count: numberOfColumns)
        
        contentHeight = 0
        for item in 0..<collectionView.numberOfItems(inSection: 0) {
            let indexPath = IndexPath(item: item, section: 0)
            

            let photoHeight = delegate?.collectionView(collectionView, heightForPhotoAtIndexPath: indexPath) ?? 180
            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)
            
            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            attributes.frame = insetFrame
            cache.append(attributes)

            contentHeight = max(contentHeight, frame.maxY)
            yOffset[column] = yOffset[column] + height

            column = column < (numberOfColumns - 1) ? (column + 1) : 0
        }
        collectionView.contentSize.height = contentHeight
        collectionView.layoutIfNeeded()
        if collectionView.contentOffset.y > contentHeight - collectionView.bounds.height {
            collectionView.scrollToItem(at: IndexPath(row:(collectionView.numberOfItems(inSection: 0)) - 1, section: 0), at: .bottom, animated: true)
        }
    }
}

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]
}

override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
    let shouldIvalidate = newBounds != self.previousBounds
    if shouldIvalidate {
        if let collectionView = self.collectionView, collectionView.bounds.width > 0 {
            let cWidth = CGFloat(numberOfColumns) * CARD_ITEM_SIZE
            let sideInsets = (collectionView.bounds.width - cWidth) / 2
            collectionView.contentInset = UIEdgeInsets(top: cellPadding, left: sideInsets, bottom: cellPadding, right: sideInsets)
            collectionView.collectionViewLayout.invalidateLayout()
        }
    }
    self.previousBounds = newBounds
    return false
}
    
}

和

func collectionView(_ collectionView: UICollectionView, heightForPhotoAtIndexPath indexPath: IndexPath) -> CGFloat {
      return CARD_ITEM_SIZE * image.size.height / image.size.width
}

希望这有助于理解这种方法。

注意。我水平使用非固定数量的元素，因为这个使用 MacCatalyst 的应用程序也适用于 MacOS，当应用程序窗口调整大小时会自动调整 UICollectionView 项的大小。在 iPhone / iPad 上也可以在任何方向使用。