Using Operation subclassing

Most often, operations that you need to perform are better encapsulated in a custom subclass of the Operation class. We have already worked with BlockOperation in the previous demo, but we saw a lot of redundancy in writing code and it's not customized. In this section, we will implement the same demo and see how we build a custom Operation class to perform the task that will be done concurrently.

How to do it...

To build a custom Operation class, perform the following steps:

1. In our Xcode project, add a new Swift file with a class, named ImageDownloader, which extends the Operation class:

   

2. In the ImageDownloader.swift file, add the following code:

         class ImageDownloader: Operation { 
             let imgURL: URL 
             var downloadedImage: UIImage? 
             init(imageURL: URL) { 
                 self.imgURL = imageURL 
             } 
        
             override func main() { 
                 if self.isCancelled { 
        ...