集合视图单元格组合布局之间不需要的空间

Question

我正在为场景使用集合视图。 我创建了一个自定义组合布局，如下所示。 但是，在滚动时，单元格的第二部分之间存在不需要的空间。 它发生在不同的细胞类型中。 我检查了间距或插图，但我无法弄清楚原因。

组成布局部分：

struct UIHelper {

  static func createLayouts(section: [SectionType], sectionIndex: Int) -> NSCollectionLayoutSection {

      switch section[sectionIndex] {
      
      case .sevenDaysWeather(_):

        // MARK: - Item
        let itemSize = NSCollectionLayoutSize(widthDimension: .absolute(70), heightDimension: .absolute(124))
        let item = NSCollectionLayoutItem(layoutSize: itemSize)

        // MARK: - Group
        let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(124))
        let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
        group.interItemSpacing = .fixed(12)

        // MARK: - Section
        let section = NSCollectionLayoutSection(group: group)
        section.orthogonalScrollingBehavior = .continuous

        // MARK: - Header
        let headerSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(24))
        let headerKind = UICollectionView.elementKindSectionHeader
        let headerElement = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: headerSize, elementKind: headerKind, alignment: .top)
  
        section.boundarySupplementaryItems = [headerElement]
        section.contentInsets = NSDirectionalEdgeInsets(top: 12, leading: 16, bottom: 20, trailing: 0)
        return section
  }
}

集合视图部分：

  
  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    
    let type = sections[indexPath.section]
    
    switch type {
    case .sevenDaysWeather(let viewModels):
      guard let sevenDaysCell = collectionView.dequeueReusableCell(withReuseIdentifier: SevenDaysCollectionViewCell.identifer, for: indexPath) as? SevenDaysCollectionViewCell else { return UICollectionViewCell()}
      sevenDaysCell.configure(with: viewModels[indexPath.row])
      return sevenDaysCell
    }
  }
  
  func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
    
    let header = collectionView.dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: HeaderCollectionReusableView.identifier, for: indexPath) as! HeaderCollectionReusableView
    header.configure(section: sections, indexPath: indexPath)
    return header
  }
}

想要的结果：

当前结果：初始 state 滚动 state

编辑：通常我在集合视图中还有两个部分。 为了使示例更清晰，我修剪了这些部分。 但是逻辑与给定示例相同。

Answer 1

过了一会儿，我意识到问题与布局组的宽度大小有关。

在我发布的初始版本中，在组合布局组属性中，我在组大小中使用了fractionalWidth 。

像这样：

// MARK: - Group

let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(124))

之后，我将组的宽度更改为绝对（宽度值）。 这修复了不需要的空间。

// MARK: - Group

let groupSize = NSCollectionLayoutSize(widthDimension: .absolute(686), heightDimension: .absolute(120))

结果：初始

滚动

绝对和小数的解释可以在Apple 的文档中找到

注意：我这样计算总宽度值：

(numberOfCells * 单元格宽度) + ((numberOfCells - 1) * interSpacingValue)

Answer 2

我这样修复它，但我想知道是否有更清洁的方法：

private func makeHorizontalSection(environment: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection {
    // Calculations
    let size = CGSize(width: 100, height: 120)
    let insets: CGFloat = 23
    let itemSpacing: CGFloat = 4
    let availableWidth = environment.container.effectiveContentSize.width - 2 * insets
    let itemAndSpaceWidth = size.width + itemSpacing
    let numberOfColumns = floor(availableWidth / itemAndSpaceWidth)
    let groupWidth: CGFloat = numberOfColumns * itemAndSpaceWidth
    
    // Item
    let itemSize = NSCollectionLayoutSize(widthDimension: .absolute(size.width), heightDimension: .fractionalHeight(1))
    let item = NSCollectionLayoutItem(layoutSize: itemSize)
    
    // Group
    let groupSize = NSCollectionLayoutSize(widthDimension: .absolute(groupWidth), heightDimension: .absolute(size.height))
    let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitems: [item])
    group.interItemSpacing = .fixed(itemSpacing)
    
    // Section
    let section = NSCollectionLayoutSection(group: group)
    section.orthogonalScrollingBehavior = .continuous
    section.contentInsets = NSDirectionalEdgeInsets(top: 0, leading: insets, bottom: 0, trailing: insets)
    return section
}