Question

I have an SSCollectionView which is modeled after NSCollectionView and UITableView. It calls a function to load each item at an indexPath.

I want to asynchronously load images into each one of those paths.

- (SSCollectionViewItem *)collectionView:(SSCollectionView *)aCollectionView itemForIndexPath:(NSIndexPath *)indexPath {

....
    [self startLoadingItem:item indexPath:indexPath];

    return item;
}

-(void)startLoadingItem:(SSCollectionViewItem *)collectionViewItem indexPath:(NSIndexPath *)indexPath
{
    [SEThreadInvocation detachNewThreadSelector:@selector(loadItem:indexPath:) toTarget:self withObjects:collectionViewItem,indexPath, nil];
}

SEThreadInvocation is just a subclass of NSThread so that I can send more than one object to a selector.

-(void)loadItem:(SSCollectionViewItem *)collectionViewItem indexPath:(NSIndexPath *)indexPath {

... 

    collectionViewItem.imageView.image = imageToDisplay;

}

What is happening is that the code initially works, but every time the collection reloads (often) it puts images all over the collection view randomly.

I believe this is because my SSCollectionViewItem is pointing to a different memory location each time and my item is not thread safe, so it is just stamping my images all over the place when they change in memory.

Also, I thought it might be replacing the images in memory, so I replaced it with numbers and the numbers bounce all over the collection view when reloading as well.

How can I make my objects thread safe in this context?

Answer 1

SSToolkit has a sample Catalog project which has a SSCollectionView demo. It loads images in the way you are needing.