swift - CollectionView 滚动到新插入的项目

Question

我有一个由 NSFetchedResultsController 驱动的 CollectionView。

CollectionViewLayout 是按名称升序排列的单元格的水平“轮播”布局。

新项目插入时带有自定义动画。

 func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {

if type == NSFetchedResultsChangeType.Insert {
    println("Insert Object: \(newIndexPath)")

   UIView.animate(withDuration: 1.0, delay: 0.0, options: .curveEaseOut, animations: {
       self.collectionView?.insertItems(at: [newIndexPath])
   }, completion: { finished in
       self.collectionView?.scrollToItem(at: newIndexPath, at: .centeredHorizontally, animated: true)
})
    )
...

它可以工作，但动画有点小故障，并且滚动同时发生。

我想滚动到 Item，然后使用自定义动画插入它，但如果我在插入之前滚动到 Item，应用程序就会崩溃。

这里应该做什么？

谢谢

Answer 1

我要尝试的第一件事是将 animate(withDuration:delay:options:animations:completion:) 替换为 performBatchUpdates(_:completion:)

func controller(controller: NSFetchedResultsController,
                didChangeObject anObject: AnyObject,
                atIndexPath indexPath: NSIndexPath?,
                forChangeType type: NSFetchedResultsChangeType,
                newIndexPath: NSIndexPath?)
{

    if type == NSFetchedResultsChangeType.Insert {
        println("Insert Object: \(newIndexPath)")

    self.collectionView?.performBatchUpdates({
        self.collectionView?.insertItems(at: [newIndexPath])
    }, completion: { finished in
        self.collectionView?.scrollToItem(at: newIndexPath, at: .centeredHorizontally, animated: true)
    })
    …
}

如果这仍然给您带来问题，那么您可以在下一个运行循环中调用滚动。

func controller(controller: NSFetchedResultsController,
                didChangeObject anObject: AnyObject,
                atIndexPath indexPath: NSIndexPath?,
                forChangeType type: NSFetchedResultsChangeType,
                newIndexPath: NSIndexPath?)
{

    if type == NSFetchedResultsChangeType.Insert {
        println("Insert Object: \(newIndexPath)")

    self.collectionView?.performBatchUpdates({
        self.collectionView?.insertItems(at: [newIndexPath])
    }, completion: { finished in
        DispatchQueue.main.async { // Defer to next runlop.
            self.collectionView?.scrollToItem(at: newIndexPath, at: .centeredHorizontally, animated: true)
        }
    })
    …
}

最后，您可以尝试仅对滚动部分进行动画处理。

func controller(controller: NSFetchedResultsController,
                didChangeObject anObject: AnyObject,
                atIndexPath indexPath: NSIndexPath?,
                forChangeType type: NSFetchedResultsChangeType,
                newIndexPath: NSIndexPath?)
{

    if type == NSFetchedResultsChangeType.Insert {
        println("Insert Object: \(newIndexPath)")

    self.collectionView?.reloadItems(at: [newIndexPath]) // reload without animating.

    DispatchQueue.main.async { // Defer to next runlop.
        self.collectionView?.scrollToItem(at: newIndexPath, at: .centeredHorizontally, animated: true)
    }
    …
}