NSCache removes all its data when app goes to background State

Question

I am working with NSCache, I am using NSCache to store images. I am showing images on UITableView. Whenever I add images first they ar

Answer 1

Yes it does that, for some reason it instantly removes data from cache when app enters background even if there is no memory pressure. To fix this you have to tell NSCache that your data should not be discarded.

Here is how you fix this.

class ImageCache: NSObject , NSDiscardableContent {

    public var image: UIImage!

    func beginContentAccess() -> Bool {
        return true
    }

    func endContentAccess() {

    }

    func discardContentIfPossible() {

    }

    func isContentDiscarded() -> Bool {
        return false
    }
}

and then use this class in NSCache like this.

let cache = NSCache<NSString, ImageCache>()

and then set the data in cache like this

let cacheImage = ImageCache()
cacheImage.image = imageDownloaded
self.cache.setObject(cacheImage, forKey: "somekey" as NSString)

and to retrive the data

if let cachedVersion = cache.object(forKey: "somekey") {
     youImageView.image = cachedVersion.image
}