Modern Concurrency: Getting Started

Oct 18 2022 · Swift 5.5, iOS 15, Xcode 13.4

Part 2: Asynchronous Sequences

11. Using Asynchronous Methods in Views

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Previous episode: 10. Concurrency With async let Next episode: 12. Displaying a Progress View

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Make sure the course server is running and continue with your project from the previous episode or open the starter project for this episode.

SuperStorage app

The download view downloads the file using your choice of subscription plan: silver, gold or Cloud 9.

Download data

In SuperStorageModel, locate download(file:). It already contains the code you know so well:

guard let url = URL(
string: "http://localhost:8080/files/download?\(file.name)") else {
  throw "Could not create the URL."
}
let (data, response) = try await URLSession.shared.data(from: url)
guard (response as? HTTPURLResponse)?.statusCode == 200 else {
  throw "The server responded with an error."
}

addDownload(name: file.name)

updateDownload(name: file.name, progress: 1.0)

return data

Call download(file:)

Now, where do you call this asynchronous method? Open DownloadView. Go to its body.

fileData = try await model.download(file: file)

let downloadSingleAction: ()  🟩async🟥 -> Void

Task {
  fileData = try await model.download(file: file)
}

@MainActor 
func addDownload(name: String) { ... }
@MainActor 
func updateDownload(name: String, progress: Double) { ... }

.onDisappear {
  fileData = nil
  model.reset()
}