Intermediate Combine

Apr 13 2021 · Swift 5.3, macOS 11.1, Xcode 12.2

Part 1: Intermediate Combine

05. Retrying and Catching Errors

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Previous episode: 04. Mapping Errors Next episode: 06. Testing Combine Operators

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There will be times in processing data where you’ll need to retry if a failure is encountered. Networking is a great example here. If a download only partially completes, you can use Combine’s retry operator to retry the download.

let photoService = PhotoService()

example(of: "Catching and retrying") {
  photoService
    .fetchPhoto(quality: .low)
    .sink(
      receiveCompletion: { print("\($0)") },
      receiveValue: { image in
        image
        print("Got image: \(image)")
      }
    )
    .store(in: &subscriptions)
}
.retry(3)
.handleEvents(
  receiveSubscription: { _ in print("Trying ...") },
  receiveCompletion: {
    guard case .failure(let error) = $0 else { return }
    print("Got error: \(error)")
  }
)
.fetchPhoto(quality: .high, failingTimes: 2)
.replaceError(with: UIImage(named: "na.jpg")!)
.catch { error -> PhotoService.Publisher in
  print("Failed fetching high quality, falling back to low quality")
  return photoService.fetchPhoto(quality: .low)
}