Swift cache base64 string UIImage data - ios

Question

I'm trying to cache UIImage that images come from service(I'm using Alamofire). Service sends me a base64 string and I'm converting base64 to data then print in tableviewcell with
cell.imageview.image = UIImage(data: imageDatas[indexPath.row])
I searched lots of libraries like Kingfisher , AlamofireImage but they are caching URL image can't find anyway to cache image with base64 string.So I find a similar example and try this :
private let cache = NSCache<NSNumber, UIImage>()
private let utilityQueue = DispatchQueue.global(qos: .utility)
private func loadImage(data : Data , completion: #escaping (UIImage?) -> ()) {
utilityQueue.async {
let image = imageDataDecodingClass.imageDataDecoding(imageData: data)
DispatchQueue.main.async {
completion(image)
}
}
}
in cell :
let itemNumber = indexPath.section * 2 + 1
let imageData = (showcaseDatas[indexPath.section * 2 + 1].Document?.Document!)!
if let cachedImage = self.cache.object(forKey: NSNumber(value: itemNumber)) {
cell.showcaseImage.image = cachedImage
} else {
cell.addSubview(progressHUDimage)
self.loadImage(data: imageData, completion: {ret in
cell.showcaseImage.image = ret
self.cache.setObject(cell.showcaseImage.image!, forKey: NSNumber(value: itemNumber))
progressHUDimage.removeFromSuperview()
})
}
Its caching image perfectly but when I scroll tableview ,CPU increased a lot (%70-90) thats why tableview is not smoothing.
So , my question is , How can I cache base64 string image in tableviewcell with smoothing and without CPU increased ? Thanks

Answer 1

If you are caching base64 String or Data there will be always a hit in decoding them as an image. The only way it would be caching the UIImage itself, but this will come with trade off of memory depending on the size of your images.
I can only give you few advices:
Use NSCache (it seems that you are already using it)
Resize your images on another thread to have a perfect fit on the size that you are rendering on screen and cache them only after they have been resized
Be sure that the performance hit you are seeing is not due to other reasons
Cache images by using their index path if you are using for cells
Create your NSCache with a memory limit and a number of element limit
You can also try to create 2 caches, one for ready to go already decode images and the other one as a fallback with Data object.
The fact that your Data objects are small it doesn't means that also images are, it really depends on the compression that has been used to save the image representation.
There are also more advance technique using memory mapping on physical memory.