dequeueReusableCellWithIdentifier not reusing cells

Question

I have a UICollectionView with a custom cell subclassing UICollectionViewCell. And in the code I have done the following:

 [self.collectionView_ registerClass:[AHPinterestCell class]
        forCellWithReuseIdentifier:@"AHPinterestCell"];

this is what goes in my cellForItem

  AHPinterestCell *cell =
                (AHPinterestCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"AHPinterestCell"
                                                                             forIndexPath:indexPath];

however, it seems that it's not reusing the cell. In my collection view per screen it is showing about 9-10 cells, however when I do infinite scroll and then I call insertItemsAtIndexPath it calls the initWithFrame method on my custom cell, while it should probably reuse the cells I already have. Why is this?

EDIT:

I am adding a sample demo project that illustrates the problem, the link to the xcode project can be found here. It's essentially doing an infinite scroll when you reach to the bottom, it just appends more stuff into it. But when you do so it's going to call the init method again.

Answer 1

In short, your code works fine. As expected, as cells scroll off the screen, they are eventually flagged as being available for reuse. And when you call dequeueReusableCellWithReuseIdentifier, if there is a cell available for reuse, it will do so. If not, it creates one.

The time that you'll see a lot of cells being created is if you scroll fast or continually. But if you do short little scrolls, let go, pause, let the UI catch up and repeat, then you'll see very few cells being created.

I interpret this as meaning that iOS prioritizes the UI and the creation of new cells over the dequeuing of old cells, allowing their reuse. So if you flip quickly, it has trouble catching up and flagging old cells as available for reuse. This is probably not altogether bad, as this is probably what gives collection views such smooth flow. Flagging old cells for reuse is one of the less important things for iOS to do here. But clearly if memory is tight, this might be a problem.

By the way, if you put a NSLog in dealloc, too, you'll notice that when the UI finally catches up after doing a really fast scroll through the collection view, it clearly has some logic that says "gee, I've got more spare cells than I really need, I'm going to get rid of some of these." It's a pretty clever implementation, actually. A focus on speed, but with some memory optimizations that take place once the UI quiets down.