UICollectionview scrollToItemAtIndexPath,在动画完成之前不加载可见单元格

Swift 3.0或更高版本

在实现scrollToItem方法之前添加"view.layoutIfNeeded()",理想情况下在viewWillAppear中

override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
view.layoutIfNeeded()
  colView.scrollToItem(at: IndexPath(item: 4, section: 0), at: .centeredHorizontally, animated: true)}

我使用dispatch_async来更新UI并且它可以工作.

let numberOfSections = self.collectionView.numberOfSections()
let numberOfRows = self.collectionView.numberOfItemsInSection(numberOfSections-1)

    if numberOfRows > 0 {
        dispatch_async(dispatch_get_main_queue(), {
            let indexPath = NSIndexPath(forRow: numberOfRows-1, inSection: (numberOfSections-1))
            self.collectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: .Bottom, animated: true)
        })
    }