ImageDownloadHelper.swift

class ImageDownloadHelper: SwiftOperation {
  //1
  let imageRecord: ImageRecord
  
  //2
  init(_ imageRecord: ImageRecord) {
    self.imageRecord = imageRecord
  }
  
  //3
  override func main() {
    //4
    if isCancelled {
      return
    }

    //5
    guard let imageData = try? Data(contentsOf: imageRecord.url) else { return }
    
    //6
    if isCancelled {
      return
    }
    
    //7
    if !imageData.isEmpty {
      imageRecord.image = UIImage(data:imageData)
      imageRecord.state = .downloaded
    } else {
      imageRecord.state = .failed
      imageRecord.image = UIImage(named: "Failed")
    }
  }
}