如何集中关注的UICollectionViewCell？

Question

我想要实现的非常简单:每次用户聚焦一个集合视图单元格时,我想让焦点单元格水平居中.似乎我目前的方法根本不起作用.

    func collectionView(collectionView: UICollectionView, didUpdateFocusInContext context: UICollectionViewFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
        guard collectionView === self.categoryCollectionView else {
            return
        }
        guard let indexPath = context.nextFocusedIndexPath else {
            return
        }

        collectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: .CenteredHorizontally, animated: true)
    }

奇怪的是,集合视图忽略了任何在任何地方滚动的尝试.出于测试目的,我将索引路径更改为集合视图中的最后一个项目的索引路径,但它仅在首次显示集合视图时有效.

Answer 1

诀窍是确保您已设置UICollectionView scrollEnabled = false.

override func didUpdateFocusInContext(context: UIFocusUpdateContext, 
  withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
    if let focusedView = context.nextFocusedView as? UITableViewCell {
      collectionView.scrollEnabled = false
      let indexPath = collectionView.indexPathForCell(focusedView)!
      collectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: .CenteredHorizontally, animated: true)
    }
}