如何在单元格之间获得更均匀的垂直距离？

Question

我已经使用自动布局（没有故事板或 xib）动态创建单元格，但布局管理器似乎是 将单元格配对，使一个短单元格和一个高单元格并排组成一排。

我想要的是让单元格之间的距离一致（垂直堆叠），而不是大的空白。因此，在左侧向下的三个连续短单元的高度和位置可能与右侧的一个大单元相同。换句话说：所有单元格之间的垂直距离一致。

  /// Everything is a side effect.  Configure the cell passed in
    ///
    /// - Parameters:
    ///   - cell: cell to format
    ///   - indexPath: index of cell
    func formatAutolayoutCell(cell: AutoResizingTextCell, at indexPath: IndexPath) {
        let event = eventsSource[indexPath.row]
        cell.layer.borderColor = event.calendar.cgColor
        cell.contentView.backgroundColor =  UIColor(cgColor: event.calendar.cgColor).withAlphaComponent(0.1)

        cell.titleLabel.text = event.title

        cell.contentView.addSubview(cell.titleLabel)
        cell.titleLabel.topAnchor.constraint(equalTo: cell.contentView.topAnchor).isActive = true
        cell.titleLabel.widthAnchor.constraint(equalToConstant: cellWidth).isActive = true
        cell.titleLabel.textColor = UIColor(cgColor: event.calendar.cgColor)
        cell.titleLabel.textAlignment = .center

        cell.contentView.addSubview(cell.bodyLabel)
        cell.bodyLabel.text = event.notes ?? ""
        cell.bodyLabel.widthAnchor.constraint(equalToConstant: cellWidth).isActive = true
        cell.bodyLabel.bottomAnchor.constraint(equalTo: cell.contentView.bottomAnchor).isActive = true
        cell.titleLabel.bottomAnchor.constraint(equalTo: cell.bodyLabel.topAnchor).isActive = true
    }

编辑：

使用Galo Torres Sevilla 的建议，我尝试使用UICollectionViewLayout。它让我更接近我的目标，但看起来单元格的数量是按列平均划分的，所以如果最左边的列有短单元格，它会“提前”用完单元格，左侧有很多空间底部。看来我可能需要按大小对单元格进行排序以获得更好的分布。

Answer 1

遵循https://www.raywenderlich.com/392-uicollectionview-custom-layout-tutorial-pinterest的代码

你可以继承 UICollectionViewFlowLayout 来获得你需要的东西。

这是它的主要代码。 注意：代码来自以上网站

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 = 6

  //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]
  }

}