UIImage that implements NSDiscardableContent

discardableThumbnail.swift

final class discardableThumbnail: NSDiscardableContent {
    var thumbnail: UIImage!
    var accessCounter: Int = 0
    
    init(image: UIImage) {
        thumbnail = image
    }
    
    func beginContentAccess() -> Bool {
        if !(self.thumbnail != nil) {
            return false
        }
        self.accessCounter += 1
        return true
    }
    
    func endContentAccess() {
        if self.accessCounter > 0 {
            self.accessCounter -= 1
        }
    }
    
    func discardContentIfPossible() {
        if self.accessCounter == 0 {
            self.thumbnail = nil
        }
    }
    
    func isContentDiscarded() -> Bool {
        return self.thumbnail == nil
    }
}