UICollectionViewCell:自动布局-大小计算不正确(偏移10磅)

我有一套 UICollectionViewCell 具有不同布局的子类(使用AutoLayout)。

由于“自调整单元格大小”功能已完全中断,因此我在 数据来源 正好是10磅 小于它应该是,不管细胞。

下面是我用来计算尺寸的代码:

  let sizeCache = CellCache() // Size cache stores previously calculated values
  func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    if let cachedSize = sizeCache.sizeAtIndexPath(indexPath: indexPath) {
      return cachedSize // Return cached value if it exists
    }

    // Calculate the size if not found in the cache
    let cellClass = cellTypeAt(indexPath: indexPath) // Get the class type
    let cell = sizeCache.createCellOfTypeIfNeeded(cellType: cellClass) // Dequeue or instantiate a cell
    self.collectionView(collectionView, cell: cell, configureAt: indexPath) // Ask DataSource to configure this cell
    let fittingSize = CGSize(width: collectionView.bounds.width - 16, height: 0) // Set the padding to 16
    cell.bounds = CGRect(origin: .zero, size: fittingSize) // Set cell's width
    var result = cell.contentView.systemLayoutSizeFitting(UIView.layoutFittingCompressedSize) // Calculate cell's size using AutoLayout
    result.width = collectionView.bounds.width - 16 // Set the padding
    result.height = result.height + 10 // !!! Error - Add 10 pt to the result !!!
    sizeCache.setSize(size: result, at: indexPath) // Cache the result
    return result
  }

注意结尾的那行 让它工作。

width 约束条件:

import UIKit
import SnapKit

class AutoSizingCellBase: UICollectionViewCell {
  override class var requiresConstraintBasedLayout: Bool {
    return true
  }

  private final var widthConstraint: Constraint?

  override func updateConstraints() {
    if widthConstraint == nil {
      if let window = window {
        let width = window.bounds.width - 16
        contentView.snp.makeConstraints { (make) in
          widthConstraint = make.width.equalTo(width).constraint
        }
      }
    }
    super.updateConstraints()
  }
}

问题的例子:

正确尺寸(添加10磅后)

尺寸不正确(未添加10磅)

这个问题影响到所有的细胞。根本原因是什么?

更新:约束示例 以下是我用于配置所示视图的约束:

  private func setupConstraints() {
    price.setContentCompressionResistancePriority(.required, for: .horizontal)
    disclosureIndicator.setContentCompressionResistancePriority(.required, for: .horizontal)
    disclosureIndicator.setContentCompressionResistancePriority(.required, for: .vertical)
    disclosureIndicator.setContentHuggingPriority(.required, for: .horizontal)
    disclosureIndicator.setContentHuggingPriority(.required, for: .vertical)

    title.snp.makeConstraints { (make) in
      make.leading.top.equalTo(contentView.layoutMarginsGuide)
      make.trailing.lessThanOrEqualTo(price.snp.leading).offset(-8)
    }

    subtitle.snp.makeConstraints { (make) in
      make.top.equalTo(title.snp.bottom).offset(8)
      make.leading.bottom.equalTo(contentView.layoutMarginsGuide)
    }

    disclosureIndicator.snp.makeConstraints { (make) in
      make.trailing.equalTo(contentView.layoutMarginsGuide)
      make.centerY.equalToSuperview()
    }

    price.snp.makeConstraints { (make) in
      make.trailing.equalTo(disclosureIndicator.snp.leading).offset(-8)
      make.centerY.equalToSuperview()
    }
  }

这是一个相当复杂的例子,但即使使用更简单的例子,问题也是可以重现的:

  private func setupConstraints() {
    button.snp.makeConstraints { (make) in
      make.width.equalToSuperview() // Button is a subview of the UIStackView
    }

    stack.snp.makeConstraints { (make) in
      make.edges.equalTo(contentView.layoutMarginsGuide)
      make.height.greaterThanOrEqualTo(150)
    }
  }

在约束中添加偏移可以解决问题,而视图层次调试器仍然显示“不明确的布局”:

subtitle.snp.makeConstraints { (make) in
  make.top.equalTo(title.snp.bottom).offset(8)
  make.leading.equalTo(contentView.layoutMarginsGuide)
  make.bottom.equalTo(contentView.layoutMarginsGuide).offset(-10) // Subtracted 10
}

问题是,在哪里 10 是从什么地方来的,现在还开着。

更新3 layoutMargins :

UIView.appearance().layoutMargins = UIEdgeInsets(top: 16, left: 16, bottom: 16, right: 16)

AppDelegate ,大小计算变得正确,尽管单元格的外观发生了变化。 UICollectionView .