Cocoa开发中NSCollectionView点击前进后退按钮无法滚动如何解决？

问题原因 #

• 未给NSCollectionViewFlowLayout设置横向滚动属性，布局默认是纵向滚动，横向没有滚动空间
• 直接调用collectionView.scrollToVisible的方式不符合AppKit的滚动层级逻辑，滚动操作应该作用在外层的NSScrollView上，或者使用集合视图自带的Item滚动方法

修复步骤 #

1. 先修改configureCollectionView方法，给布局添加横向滚动配置：

private func configureCollectionView() {
  let flowLayout = NSCollectionViewFlowLayout()
  // 新增这一行 设置横向滚动
  flowLayout.scrollDirection = .horizontal
    
  flowLayout.itemSize = NSSize(width: 160.0, height: 160.0)
  flowLayout.minimumInteritemSpacing = 10.0
  flowLayout.minimumLineSpacing = 10.0
  collectionView.collectionViewLayout = flowLayout

  view.wantsLayer = true
  collectionView.layer?.backgroundColor = NSColor.red.cgColor
}

2. 替换按钮点击的实现，两种方案可选：

方案1：固定偏移量滚动 #

@IBAction func buttonLeft(_ sender: Any) {
    let currentOffset = scrollView.contentView.bounds.origin.x
    let newOffset = max(0, currentOffset - 100)
    scrollView.contentView.scroll(to: NSPoint(x: newOffset, y: 0))
    scrollView.reflectScrolledClipView(scrollView.contentView)
}

@IBAction func buttonRight(_ sender: Any) {
    let currentOffset = scrollView.contentView.bounds.origin.x
    let maxOffset = collectionView.frame.width - scrollView.bounds.width
    let newOffset = min(maxOffset, currentOffset + 100)
    scrollView.contentView.scroll(to: NSPoint(x: newOffset, y: 0))
    scrollView.reflectScrolledClipView(scrollView.contentView)
}

方案2：按单个Item滚动（不会出现半元素显示的情况，体验更好） #

@IBAction func buttonLeft(_ sender: Any) {
    guard let firstVisibleIndex = collectionView.indexPathsForVisibleItems().sorted().first, 
          firstVisibleIndex.item > 0 else { return }
    let targetIndex = IndexPath(item: firstVisibleIndex.item - 1, section: 0)
    collectionView.scrollToItems(at: [targetIndex], scrollPosition: .leading, animated: true)
}

@IBAction func buttonRight(_ sender: Any) {
    guard let lastVisibleIndex = collectionView.indexPathsForVisibleItems().sorted().last, 
          lastVisibleIndex.item < availableUsers.count - 1 else { return }
    let targetIndex = IndexPath(item: lastVisibleIndex.item + 1, section: 0)
    collectionView.scrollToItems(at: [targetIndex], scrollPosition: .trailing, animated: true)
}

内容的提问来源于stack exchange，提问作者iosSwift