NSData init?(contentsOf url: URL) migration from Swift 2 to Swift 3

Question

New to iOS/Swift. I am trying to migrate a project (that simply fetches contents from a URL via the NSData init() method) from Swift 2 to Swift 3. The original code looks like this:

let loadedImageData = NSData(contentsOfURL: imageURL)
            dispatch_async(dispatch_get_main_queue()) {
                if imageURL == user.profileImageURL {
                    if let imageData = loadedImageData  {
                        self.profileImageView?.image = UIImage(data: imageData)
                    }
                }
            }

Swift 3 migration:

 let loadedImageData = NSData(contentsOf: imageURL as URL)
            DispatchQueue.main.async {
                if imageURL == user.profileImageURL {
                    if let imageData = loadedImageData  {
                        self.profileImageView?.image = UIImage(data: imageData as Data)
                    }
                }
            }

I am not sure as to why we need to cast the NSData return value as a URL and then cast that return again to a Data type while loading the image within Swift 3. We are assigning the raw data to a variable loadedImageData in both the version. Why the casting then? It seems that the UIImage init() method needs a data object within Swift 3. However for Swift 2 there is no casting for the same. Why is that?

Thanks for the help.

Solution

The migration consists of some changes in those methods' signatures, namely, the types they accept.

In Swift 2, NSData(contentsOfURL:) and UIImage(data:) take NSURL and NSData, respectively.

Currently, they have been changed to NSData(contentsOf:) and UIImage(data:) that accept, respectively, URL (struct) and Data (instead of NSData); as a result, the casts are necessary unless you constructed your URL from type URL instead of NSURL.

You could use, instead, Data(contentsOf: URL) to avoid the cast as well.

Comments

[user2511882]

ahhh i see...the URL is actually being built as an optional NSUrl variable..that does make sense. Where can we find the documentation for swift 2.0 API' s and the respective changes. I am referring this: developer.apple.com/reference/foundation/nsdata. But this doesn't show the changes for the init method from 2.0 to 3.0. Thanks!!