SDWebImage - SDWebImagePrefetcher not using transformDownloadedImage

Question

I am currently successfully using 'SDWebImageManager downloadImageWithURL' for downloading single images , followed by the delegate method 'transformDownloadedImage' automatically called upon completion to resize the images before caching them.

I would like, however, in the background to prefetch a bunch of images (~25) not yet displayed using the prefetcher code below in a similar way. However the problem is that the 'transformDownloadedImage' delegate is not called upon completion (of 1 or all the images) - images are cached as is.

    SDWebImagePrefetcher *prefetcher = [SDWebImagePrefetcher sharedImagePrefetcher];
    [prefetcher prefetchURLs:array progress:nil completed:^(NSUInteger completedNo, NSUInteger skippedNo) {
    }];

Am I missing something? or is there some other efficient way to do this by pulling out the cached images upon completion, resizing, and reinserting? I am using "UIImage+Resize" to resize and manipulate, and obviously this needs to happen in background without blocking the UI.

Any and all advice about how to go about this efficiently will be greatly appreciated!

Answer 1

If you look at the implementation of SDWebImagePrefetcher you'll notice that it's using SDWebImageManager to perform the downloads, and it's available as a property. So you should be able to do something like this:

prefetcher.manager.delegate = self;

Now you can implement the downloadImageWithURL delegate method as you did before. I didn't try it but it should work.