URLSession CheatSheet

urlSession-cheatSheet.md

URLSession Cheatsheet

참고 https://github.com/alexpaul/iOS-UIKit/blob/main/URLSession-Cheatsheet.md

Vocabulary

• JSON
• endpoint
• RESTFul API
• URLSession
• URLSession.shared
• JSONDecoder, JSONEncoder
• URL
• URLRequest
• URLResponse
• HTTPURLResponse
• Status Code
• Data
• Codable
• Encodable
• Decodable
• HTTP methods: GET, POST, PUT, DELETE, PATCH, UPDATE
• Asynchronous
• Result
• @escaping closures
• capture list e.g [weak self], [unowned self]
• weak vs unowned

Using a closure to capture the Result of the asynchronous network request

Result type is an enum type that has two arguments, a success state and an failure state.

func fetchWebData(completion: @escaping (Result<[ModelObject], Error>) -> ()) {
 // netowrking code here
}

Perform a GET request using URLSession

URLSession.shared is a singleton instance on URLSession with basic networking configurations.

let dataTask = URLSession.shared.dataTask(with: url) { (data, response, error) in
  // networking code here
}
dataTask.resume()

Check that the HTTPURLResponse status code is within the valid range of 200...299 indicating a successful response

guard let httpResponse = response as? HTTPURLResponse,
      (200...299).contains(httpResponse.statusCode) else {
  print("bad status code")
  return
}

Converting JSON data to Swift objects

do {
  let topLevelModel = try JSONDecoder().decode(TopLevelModel.self, from: jsonData)
  let modelObjects = topLevelModel.modelObjects
  completion(.success(modelObjects)
} catch {
  // decoding error
  completion(.failure(error))
}

Using the Codable protocol to parse JSON to Swift model(s)

struct CovidCountriesWrapper: Codable {
  let countries: [CountrySummary]
  
  // CodingKeys allows us to rename properties
  enum CodingKeys: String, CodingKey {
    case countries = "Countries"
  }
}

struct CountrySummary: Codable {
  let country: String
  let totalConfirmed: Int
  let totalRecovered: Int
  
  enum CodingKeys: String, CodingKey {
    case country = "Country"
    case totalConfirmed = "TotalConfirmed"
    case totalRecovered = "TotalRecovered"
  }
}

The CodingKeys built-in enum type allows us to change JSON property names to our own custom names

In this example we change Countries to a more Swift naming conventional name countries.

struct CovidCountriesWrapper: Codable {
  let countries: [CountrySummary]
  
  // CodingKeys allows us to rename properties
  enum CodingKeys: String, CodingKey {
    case countries = "Countries"
  }
}

Completed API Client to fetch web data

 func fetchWebData(completion: @escaping (Result<[ModelObject], Error>) -> ()) {
    // 1. - endpoint URL string
    let endpointURLString = "https://........"
    
    // 2. - convert the string to an URL
    guard let url = URL(string: endpointURLString) else {
      print("bad url")
      return
    }
    
    // URL vs URLRequest
    
    // 3. - make the request using URLSession
    // .shared is an singleton instance on URLSession comes with basic configuration needed for most requests
    let dataTask = URLSession.shared.dataTask(with: url) { (data, response, error) in
      if let error = error {
        return completion(.failure(error))
      }
      
      // first we have to type cast URLResponse to HTTPURLRepsonse to get access to the status code
      // we verify the that status code is in the 200 range which signals all went well with the GET request
      guard let httpResponse = response as? HTTPURLResponse,
            (200...299).contains(httpResponse.statusCode) else {
        print("bad status code")
        return
      }
      
      if let jsonData = data {
        // convert data to our swift model
        do {
          let topLevelModel = try JSONDecoder().decode(TopLevelModel.self, from: jsonData)
          let modelObjects = topLevelModel.modelObjects
          completion(.success(modelObjects))
        } catch {
          // decoding error
          completion(.failure(error))
        }
      }
    }
    dataTask.resume()
  }