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Error handling with dataTaskPublisher.

Forums > SwiftUI

Hey guys, I am currently learning about Combine framework and how to use it. I am quite amazed but there are some things that still make me feel dull.

For example. I've got that network call that I am working on.

private func fetchFollowersAppleWay() {

      guard let url = URL(string: endPointString) else { return }

      let decoder = JSONDecoder()
      decoder.keyDecodingStrategy = .convertFromSnakeCase

      var fetchFollowersCancellable = URLSession.shared
         .dataTaskPublisher(for: url)
         .tryMap { element -> Data in
            guard let httpResponse = element.response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
               throw URLError(.badServerResponse)
         .decode(type: [Follower].self, decoder: decoder)
         .sink { error in
            self.fetchingError = error
            // Cannot assign value of type 'Subscribers.Completion<Error>' to type 'Error?'
         } receiveValue: { followers in
            self.followers = followers

My main point right now, is to handle errors as well as possible. With UIKit, I would have handled it like this:

let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
            if let _ = error { completed(.failure(.unableToComplete))}

            guard let response = response as? HTTPURLResponse, response.statusCode == 200 else { completed(.failure(.invalidResponse)); return}

            guard let data = data else { completed(.failure(.invalidData)); return}

            do {
                let decoder = JSONDecoder()
                decoder.keyDecodingStrategy = .convertFromSnakeCase
                let followers = try decoder.decode([Follower].self, from: data)
            } catch { completed(.failure(.invalidData)) }

I am not sure how to handle errors properly with that newer Publisher. Any help appreciated, thanks!


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