URLSession Calls in Swift 4

URLSession Calls in Swift 4

func makeGetCall() {
  // Set up the URL request
  let todoEndpoint: String = "https://jsonplaceholder.typicode.com/todos/1"
  guard let url = URL(string: todoEndpoint) else {
    print("Error: cannot create URL")
    return
  }
  let urlRequest = URLRequest(url: url)

  // set up the session
  let config = URLSessionConfiguration.default
  let session = URLSession(configuration: config)

  // make the request
  let task = session.dataTask(with: urlRequest) {
    (data, response, error) in
    // check for any errors
    guard error == nil else {
      print("error calling GET on /todos/1")
      print(error!)
      return
    }
    // make sure we got data
    guard let responseData = data else {
      print("Error: did not receive data")
      return
    }
    // parse the result as JSON, since that's what the API provides
    do {
      guard let todo = try JSONSerialization.jsonObject(with: responseData, options: [])
        as? [String: Any] else {
          print("error trying to convert data to JSON")
          return
      }
      // now we have the todo
      // let's just print it to prove we can access it
      print("The todo is: " + todo.description)

      // the todo object is a dictionary
      // so we just access the title using the "title" key
      // so check for a title and print it if we have one
      guard let todoTitle = todo["title"] as? String else {
        print("Could not get todo title from JSON")
        return
      }
      print("The title is: " + todoTitle)
    } catch  {
      print("error trying to convert data to JSON")
      return
    }
  }
  task.resume()
}

func makePostCall() {
  let todosEndpoint: String = "https://jsonplaceholder.typicode.com/todos"
  guard let todosURL = URL(string: todosEndpoint) else {
    print("Error: cannot create URL")
    return
  }
  var todosUrlRequest = URLRequest(url: todosURL)
  todosUrlRequest.httpMethod = "POST"
  let newTodo: [String: Any] = ["title": "My First todo", "completed": false, "userId": 1]
  let jsonTodo: Data
  do {
    jsonTodo = try JSONSerialization.data(withJSONObject: newTodo, options: [])
    todosUrlRequest.httpBody = jsonTodo
  } catch {
    print("Error: cannot create JSON from todo")
    return
  }

  let session = URLSession.shared

  let task = session.dataTask(with: todosUrlRequest) {
    (data, response, error) in
    guard error == nil else {
      print("error calling POST on /todos/1")
      print(error!)
      return
    }
    guard let responseData = data else {
      print("Error: did not receive data")
      return
    }

    // parse the result as JSON, since that's what the API provides
    do {
      guard let receivedTodo = try JSONSerialization.jsonObject(with: responseData,
        options: []) as? [String: Any] else {
          print("Could not get JSON from responseData as dictionary")
          return
      }
      print("The todo is: " + receivedTodo.description)

      guard let todoID = receivedTodo["id"] as? Int else {
        print("Could not get todoID as int from JSON")
        return
      }
      print("The ID is: \(todoID)")
    } catch  {
      print("error parsing response from POST on /todos")
      return
    }
  }
  task.resume()
}

func makeDeleteCall() {
  let firstTodoEndpoint: String = "https://jsonplaceholder.typicode.com/todos/1"
  var firstTodoUrlRequest = URLRequest(url: URL(string: firstTodoEndpoint)!)
  firstTodoUrlRequest.httpMethod = "DELETE"

  let session = URLSession.shared

  let task = session.dataTask(with: firstTodoUrlRequest) {
    (data, response, error) in
    guard let _ = data else {
      print("error calling DELETE on /todos/1")
      return
    }
    print("DELETE ok")
  }
  task.resume()
}

If you're using this in a playground, add this at the top:

import PlaygroundSupport

and this at the end:

PlaygroundPage.current.needsIndefiniteExecution = true

(Thanks @gregoriomelo)

I have a question. How do I return a value from this
func makeGetCall() {
// Set up the URL request

so I can put it into a storyboard label and print it out?

Hi ShanghaiTimes,
As URLSessionDataTask is an asynchronous method you will have to pass a closure (aka completionHandler) as a parameter in makeGetCall() method. Once the response is obtained you can pass the value in this closure.

eg:

func makeGetCall(completionHandler: (Int) -> ()) {
/// All previous code
//
//
print("The todo is: " + receivedTodo.description)
guard let todoID = receivedTodo["id"] as? Int else {
print("Could not get todoID as int from JSON")
return
}
completionHandler(todoID)
} catch {
/// Remaining code
///
///
}

and this is how you make a call to the makeGetCall function:

makeGetCall() { todoTitle in
print("The title is: " + todoTitle)
}

I found this gist useful! When testing it against a toy API I built (instead of against jsonplaceholder) I found that I needed to set the content-type header explicitly on my POST requests. I added this line after todosUrlRequest.httpMethod = "POST":

todosUrlRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")

Sharing my discovery here in case it helps someone else in their travels

Hi ,
I try to get HTML code from a web page behind a user login password page.
The users and password is sent into the URL at the first connexion. The web Site give me 3 cookie.

when a call the func with completionHandler(htmlinfo) i got an error from my website who tell me that i'm not authentificate (problem of cookiee )

do you know how i could keep cookie from the func ?

func makeGetCall() {
  // Set up the URL request
  let todoEndpoint: String = "https://jsonplaceholder.typicode.com/todos/1"
  guard let url = URL(string: todoEndpoint) else {
    print("Error: cannot create URL")
    return
  }
  let urlRequest = URLRequest(url: url)

  // set up the session
  let config = URLSessionConfiguration.default
  let session = URLSession(configuration: config)

  // make the request
  let task = session.dataTask(with: urlRequest) {
    (data, response, error) in
    // check for any errors
    guard error == nil else {
      print("error calling GET on /todos/1")
      print(error!)
      return
    }
    // make sure we got data
    guard let responseData = data else {
      print("Error: did not receive data")
      return
    }
    // parse the result as JSON, since that's what the API provides
    do {
      guard let todo = try JSONSerialization.jsonObject(with: responseData, options: [])
        as? [String: Any] else {
          print("error trying to convert data to JSON")
          return
      }
      // now we have the todo
      // let's just print it to prove we can access it
      print("The todo is: " + todo.description)

      // the todo object is a dictionary
      // so we just access the title using the "title" key
      // so check for a title and print it if we have one
      guard let todoTitle = todo["title"] as? String else {
        print("Could not get todo title from JSON")
        return
      }
      print("The title is: " + todoTitle)
    } catch  {
      print("error trying to convert data to JSON")
      return
    }
  }
  task.resume()
}

func makePostCall() {
  let todosEndpoint: String = "https://jsonplaceholder.typicode.com/todos"
  guard let todosURL = URL(string: todosEndpoint) else {
    print("Error: cannot create URL")
    return
  }
  var todosUrlRequest = URLRequest(url: todosURL)
  todosUrlRequest.httpMethod = "POST"
  let newTodo: [String: Any] = ["title": "My First todo", "completed": false, "userId": 1]
  let jsonTodo: Data
  do {
    jsonTodo = try JSONSerialization.data(withJSONObject: newTodo, options: [])
    todosUrlRequest.httpBody = jsonTodo
  } catch {
    print("Error: cannot create JSON from todo")
    return
  }

  let session = URLSession.shared

  let task = session.dataTask(with: todosUrlRequest) {
    (data, response, error) in
    guard error == nil else {
      print("error calling POST on /todos/1")
      print(error!)
      return
    }
    guard let responseData = data else {
      print("Error: did not receive data")
      return
    }

    // parse the result as JSON, since that's what the API provides
    do {
      guard let receivedTodo = try JSONSerialization.jsonObject(with: responseData,
        options: []) as? [String: Any] else {
          print("Could not get JSON from responseData as dictionary")
          return
      }
      print("The todo is: " + receivedTodo.description)

      guard let todoID = receivedTodo["id"] as? Int else {
        print("Could not get todoID as int from JSON")
        return
      }
      print("The ID is: \(todoID)")
    } catch  {
      print("error parsing response from POST on /todos")
      return
    }
  }
  task.resume()
}

func makeDeleteCall() {
  let firstTodoEndpoint: String = "https://jsonplaceholder.typicode.com/todos/1"
  var firstTodoUrlRequest = URLRequest(url: URL(string: firstTodoEndpoint)!)
  firstTodoUrlRequest.httpMethod = "DELETE"

  let session = URLSession.shared

  let task = session.dataTask(with: firstTodoUrlRequest) {
    (data, response, error) in
    guard let _ = data else {
      print("error calling DELETE on /todos/1")
      return
    }
    print("DELETE ok")
  }
  task.resume()
}

Applied swift syntax highlight.