Combine Demo

combine_demo.swift

// h/t to @JohnSundell (https://www.swiftbysundell.com/)
import UIKit
import Combine
import PlaygroundSupport

// This playground will execute indefinetly in order to give our
// async operations enough time to execute.
PlaygroundPage.current.needsIndefiniteExecution = true


// --- Creating a publisher for performing a network request ---
//     Note: set a retry automatically (3x) if request fails

let url = URL(string: "https://api.github.com/repos/67443-Mobile-Apps/RepoBrowser2022")!
// for class exercise, change the url to:
// let url = URL(string: "https://api.github.com/search/repositories?q=language:swift&sort=stars&order=desc")!
let publisher = URLSession.shared
  .dataTaskPublisher(for: url)
  .retry(3)


// --- Bringing back our old friend, Repository ---

struct Repository: Codable, Identifiable {
  let id: Int
  let name: String
  let htmlURL: String
  let itemDescription: String?
  
  enum CodingKeys: String, CodingKey {
    case id
    case name
    case htmlURL = "html_url"
    case itemDescription = "description"
  }
}


// --- Subscribing to our publisher using sink() ---

let cancellableSubscriber = publisher.sink(
  receiveCompletion: { completion in
    switch completion {
      case .failure(let error):
          print(error)
      case .finished:
          print("Success")
    }
  },
  receiveValue: { value in
    let decoder = JSONDecoder()

    do {
      // Since each value passed into our closure will be a tuple
      // containing the downloaded data, as well as the network
      // response itself, we're accessing the 'data' property here:
      let repo = try decoder.decode(Repository.self, from: value.data)
      print(repo)
    } catch {
      print(error)
    }
  }
)

// --- Constructing a reactive chain of operators ---

let repoPublisher = publisher
    .map(\.data)
    .decode(
        type: Repository.self,
        decoder: JSONDecoder()
    )
    .receive(on: DispatchQueue.main)


// --- Updating our UI based on our reactive chain ---

// Two labels that we want to render our data using:
let nameLabel = UILabel()
let urlLabel = UILabel()
let errorLabel = UILabel()

let cancellableRepoSubscriber = repoPublisher.sink(
  receiveCompletion: { completion in
      switch completion {
      case .failure(let error):
          // Rendering a description of the error that was encountered:
          errorLabel.text = error.localizedDescription
          print("ErrorMsg: \(error.localizedDescription)")
      case .finished:
          break
      }
  },
  receiveValue: { repo in
      // Rendering the downloaded repository's name and url:
      nameLabel.text = repo.name
      urlLabel.text = repo.htmlURL
      print("Name: \(repo.name)")
      print("URL:  \(repo.htmlURL)")
  }
)