UICollectionView insertItemsAtIndexPaths：似乎重新加载collectionview或自动滚动到顶部

Question

I am using a UICollectionView in combination with a NSFetchedResultsController . When I fetch new data, I throw them in a SQLite database and my frc gets a notification that it will update. I implement the appropriate delegate methods and insert the new data in a batch update and I don't call reloadData afterwards. But as soon as the data is inserted, the collectionview scrolls to the top (to make the new items visible?). I would like to interfere this process and imitate the Facebook/9Gag implementation. When there is new data, a button is faded in which lets the user scroll to the top. At the time the button is shown, the new items are already inserted, so the user can also just scroll up himself. I tried the following:

• hooking into the UIScrollViewDelegate methods to see if I could stop the collectionView from scrolling (none of the methods is called during this update process)
• show the "scroll to show more"-button when the frc willUpdate and just insert the items when the button is pressed. The problem is that the user cannot scroll up himself
• Before inserting the items, I calculate the indexPath of currently visible items AFTER the insertion (adding the number of inserted items) and scroll to that index without animation in the completion block of the batch update. This only works if I delay the scrolling, but then it flickers, because it's first scrolling up a little

Answer 1

I experimented the same problem, by calling "insertItemAtIndexPaths" to increment data into my collectionView.

I noticed two things : - If you add items AFTER the current visible index path, there's no automatic scroll - If you add items BEFORE the current visible index path, there's no automatic scroll, like you said, but the contentOffset is kept at the same position, but with different contentSize, because you've just added new items.

To deal with this "side effect", I used the solution mentioned here : UICollectionView insert cells above maintaining position (like Messages.app)

As it's explained in the following post, the "CATransaction.setDisableAction(false)" is the key thing to update smoothly the contentOffset position.