view model that uploads data to a server and emits events using combine in swift

To view the model that uploads data to a server and emits events using Combine in Swift, you need to create a Combine Publisher for the API call, and then subscribe to it, to receive the results.

Here is an example of how you can use the URLSession and Combine frameworks to upload data to a server and emit the results as events:


main.swift
import Foundation
import Combine

struct UploadResult {
    let success: Bool
    let message: String
}

class UploadModel {
    let uploadURL = URL(string: "https://example.com/api/upload")!
    
    func uploadData(_ data: Data) -> AnyPublisher<UploadResult, Error> {
        let request = URLRequest(url: uploadURL)
        
        // Create a Combine publisher for the API call
        return URLSession.shared.uploadTaskPublisher(for: request, from: data)
            .tryMap { data, response in
                // Process the server response
                guard let httpResponse = response as? HTTPURLResponse,
                      (200..<300) ~= httpResponse.statusCode else {
                    throw UploadError.serverError
                }
                let message = try JSONDecoder().decode(UploadMessage.self, from: data)
                return UploadResult(success: true, message: message.result)
            }
            .mapError { error in
                // Handle API call error
                return UploadError.connectionError(error)
            }
            .eraseToAnyPublisher()
    }
}
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Here, we have created the UploadModel class, which has a function uploadData that accepts a Data object and returns a Combine Publisher for the API call. The URLSession.shared.uploadTaskPublisher method is used to create the Publisher.

In the publisher's tryMap closure, we process the server response and if everything seems fine, create an UploadResult object with the result data. We then map any errors to UploadError cases using the mapError operator.

Finally, we use the eraseToAnyPublisher method to erase the specific publisher's type and make it a generic AnyPublisher, which we can freely use in our application's UI layer.

Now, to consume the publisher, you can subscribe to it, like this:


main.swift
let model = UploadModel()
let data = "Hello, World!".data(using: .utf8)!
let cancellable = model.uploadData(data)
    .sink(receiveCompletion: { completion in
        // Handle API call completion
        switch completion {
        case .finished:
            print("Upload completed!")
        case .failure(let error):
            print("Upload failed: \(error.localizedDescription)")
        }
    }, receiveValue: { result in
        // Handle API call result
        print("Result received: \(result.message)")
    })
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In this example, we create an instance of the UploadModel class, and generate some data to upload. We then call the uploadData method of the model instance to emit events as the upload progresses.

The sink operator is used to subscribe to the Publisher. The closure that is passed to sink will receive the events as they are emitted. The cancellable returned by the sink operator can be used to cancel the subscription at any time.

Hopefully, this gives you a basic idea of how to view a model that uploads data to a server and emits events using Combine in Swift.

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related categories

swift

combine

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