DiffableDataSource -是否有一种方法来限制仅在同一节中执行重新排序？

Question

在视图中，苹果展示了一个关于如何使用DiffableDataSource执行重新排序的简单示例

ReorderableListViewController.swift

dataSource.reorderingHandlers.canReorderItem = { item in return true }
dataSource.reorderingHandlers.didReorder = { [weak self] transaction in
    guard let self = self else { return }
    
    // method 1: enumerate through the section transactions and update
    //           each section's backing store via the Swift stdlib CollectionDifference API

    if self.reorderingMethod == .collectionDifference {

        for sectionTransaction in transaction.sectionTransactions {
            let sectionIdentifier = sectionTransaction.sectionIdentifier
            if let previousSectionItems = self.backingStore[sectionIdentifier],
                let updatedSectionItems = previousSectionItems.applying(sectionTransaction.difference) {
                self.backingStore[sectionIdentifier] = updatedSectionItems
            }
        }
    
    // method 2: use the section transaction's finalSnapshot items as the new updated ordering
        
    } else if self.reorderingMethod == .finalSnapshot {

        for sectionTransaction in transaction.sectionTransactions {
            let sectionIdentifier = sectionTransaction.sectionIdentifier
            self.backingStore[sectionIdentifier] = sectionTransaction.finalSnapshot.items
        }
    }
}

有什么办法，限制重新排序只能在同一节内执行吗？

在reorderingHandlers.canReorderItem中我们所能做的不多，因为闭包参数item引用的是我们正在拖动的当前源项。没有关于目标项的信息，我们可以与其进行比较，以决定是否返回true或false。

Answer 1

对于数据源来说，这种行为不是一个问题。这是你的代表的问题

可以使用:targetIndexPathForMoveFromItemAt:toProposedIndexPath:)来确定是否允许移动。

func collectionView(_ collectionView: UICollectionView, 
targetIndexPathForMoveFromItemAt originalIndexPath: IndexPath, 
         toProposedIndexPath proposedIndexPath: IndexPath) -> IndexPath {

    let sourceSection = sourceIndexPath.section
    let destSection = proposedDestinationIndexPath.section

    var destination = proposedDestinationIndexPath

    if destSection < sourceSection {
        destination = IndexPath(item: 0, section: sourceSection)
    } else if destSection > sourceSection {
        destination = IndexPath(item: self.backingStore[sourceSection].count-1, section: sourceSection)
    }

    return destination
}

这限制了项目的移动到它自己的部分。

Answer 2

如果您的项目有标题，这里有一种不同的方法：

dataSource.reorderingHandlers.canReorderItem = {item in 
    let exclude = ["Library","Favorites","Recents","Search","All"]
    if(exclude.contains(item.title!)){return false}
    return true
}

Answer 3

您也可以在委托方法collectionView(_:targetIndexPathForMoveFromItemAt:toProposedIndexPath:)中使用这种记录。

func collectionView(_ collectionView: UICollectionView, targetIndexPathForMoveFromItemAt originalIndexPath: IndexPath, toProposedIndexPath proposedIndexPath: IndexPath) -> IndexPath {
        if originalIndexPath.section != proposedIndexPath.section {
            return originalIndexPath
        }
        return proposedIndexPath
}

我在Matt关于编程iOS 14的书中读到了这篇文章，它工作得很好：)