How to cache CollectionViewCell images that is part of custom UITableViewCell - ios

Question

So, I have this news feed structure. Every news block is a custom UITableViewCell. Now, every custom cell has a CollectionView that shows images.
The problem is that when scrolling, and news cell (news block) comes out visible, the CollectionView is reloading - every time cell shows up. I'm trying to find the way to cache those images on the main ViewController side.
What would be the best approach?

Answer 1

If you want to avoid implementing your own cache/disk/memory handlers for this kind of job I strongly recommend either AFNetworking or SDWebImage that handle it all for you.
An example of SDWebImage on how to set an image and its cache:
[imageView sd_setImageWithURL:[NSURL URLWithString:#"http://www.domain.com/path/to/image.jpg"]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
This handles all the cache/disk/memory for you automatically.
Here is example of how you handle cache with SDWebImage:
// Set memory size limit (check with older devices to avoid memory errors when setting it to high value.)
[[SDImageCache sharedImageCache] setMaxMemoryCost:****];
// Clear disk cache
[[SDImageCache sharedImageCache] clearDiskOnCompletion:^{
}];
// Clear memory cache
[[SDImageCache sharedImageCache] clearMemory];
I would stay away from NSUserDefaults or the above mentioned example setting the images to dictionary or arrays to avoid memory errors and app crashes/performance.

Answer 2

You have to cache your UIImage instance, so, if you get some pictures from any source, you might write something like below:
/* some code before */
UIImage *yourImage = /* Get your UIImage from any available way */
[self.cache setObject:yourImage forKey:#"SomeUniqueID"];
/* some code after */
I guess, this code will look greater as a function, which obtains UIImage instance and it's id as parameters.
For my opinion, it's the most common way to store images. If you need a more proficient way without any overheads with third-party frameworks, you can read the documentation about NSCache.
But in general, you have a lot of different ways how to store your images:
Get the image from the disk
Get the image from the memory
Use one of the variants above, but apart them still use some lightweight & flexible frameworks, you can find a lot of on the GitHub.
So, the code I wrote above will just store images into the memory cache.