[ios] Make REST API call in Swift

I'm trying to use Swift to make a GET call to a REST API, and have tried to follow numerous tutorials, but can't figure it out. Either because I cannot figure out how to translate all the Obj-C to Swift, or because half of the methods n' such are deprecated. Does anyone know how to make the call, and parse returned JSON data?

Swift 4

Create an app using Alamofire with Api Post method

Install pod file -pod 'Alamofire', '~> 4.0' for Swift 3 with Xcode 9

Create Webservices.swift class, import Alamofire

Design storyBoard ,Login View

insert following Code for the ViewControllerClass

import UIKit

class ViewController: UIViewController {

    @IBOutlet var usernameTextField: UITextField!

    @IBOutlet var passwordTextField: UITextField!
    var usertypeStr :String = "-----------"
    var loginDictionary : NSDictionary?
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func loginButtonClicked(_ sender: Any) {
        WebServices.userLogin(userName: usernameTextField.text!, password: passwordTextField.text!,userType: usertypeStr) {(result, message, status )in
            if status {
                let loginDetails = result as? WebServices
                self.loginDictionary = loginDetails?.loginData
                if self.loginDictionary?["status"] as? String == "error"
                {
                    self.alertMessage(alerttitle: "Login Error", (self.loginDictionary?["message"] as? String)!)
                } else if self.loginDictionary?["status"] as? String == "ok" {
                    self.alertMessage(alerttitle: "", "Success")

                }else {
                    self.alertMessage(alerttitle: "", (self.loginDictionary?["message"] as? String)!)
                }
            } else {
                self.alertMessage(alerttitle: "", "Sorry")
            }
        }
    }

    func alertMessage(alerttitle:String,_ message : String){
        let alertViewController = UIAlertController(title:alerttitle,  message:message, preferredStyle: .alert)
        alertViewController.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
        present(alertViewController, animated: true, completion: nil)
    }

}

Insert Following Code For WebserviceClass

import Foundation
import Alamofire
class WebServices: NSObject {
    enum WebServiceNames: String {
        case baseUrl = "https://---------------"
        case UserLogin = "------------"
    }

    // MARK: - Login Variables
    var loginData : NSDictionary?

    class func userLogin(userName: String,password : String,userType : String, completion : @escaping (_ response : AnyObject?, _ message: String?, _ success : Bool)-> ()) {
        let url = WebServiceNames.baseUrl.rawValue + WebServiceNames.UserLogin.rawValue
        let params = ["USER": userName,"PASS":password,"API_Key" : userType]
        WebServices.postWebService(urlString: url, params: params as [String : AnyObject]) { (response, message, status) in
            print(response ?? "Error")
            let result = WebServices()
            if let data = response as? NSDictionary {
                print(data)
                result.loginData = data
                completion(result, "Success", true)

            }else {
                completion("" as AnyObject?, "Failed", false)
            }
        }
    }
    //MARK :- Post
    class func postWebService(urlString: String, params: [String : AnyObject], completion : @escaping (_ response : AnyObject?, _ message: String?, _ success : Bool)-> Void) {
        alamofireFunction(urlString: urlString, method: .post, paramters: params) { (response, message, success) in
            if response != nil {
                completion(response as AnyObject?, "", true)
            }else{
                completion(nil, "", false)
            }
        }
    }

    class func alamofireFunction(urlString : String, method : Alamofire.HTTPMethod, paramters : [String : AnyObject], completion : @escaping (_ response : AnyObject?, _ message: String?, _ success : Bool)-> Void){

        if method == Alamofire.HTTPMethod.post {
            Alamofire.request(urlString, method: .post, parameters: paramters, encoding: URLEncoding.default, headers: nil).responseJSON { (response:DataResponse<Any>) in

                print(urlString)

                if response.result.isSuccess{
                    completion(response.result.value as AnyObject?, "", true)
                }else{
                    completion(nil, "", false)
                }
            }

        }else {
            Alamofire.request(urlString).responseJSON { (response) in

                if response.result.isSuccess{
                    completion(response.result.value as AnyObject?, "", true)
                }else{
                    completion(nil, "", false)
                }
            }
        }
    }



    //Mark:-Cancel
    class func cancelAllRequests()
    {
        Alamofire.SessionManager.default.session.getTasksWithCompletionHandler { dataTasks, uploadTasks, downloadTasks in
            dataTasks.forEach { $0.cancel() }
            uploadTasks.forEach { $0.cancel() }
            downloadTasks.forEach { $0.cancel() }
        }
    }
}

func getAPICalling(mainUrl:String) {
    //create URL
    guard let url = URL(string: mainUrl) else {
      print("Error: cannot create URL")
      return
    }
    //create request
    let urlRequest = URLRequest(url: url)
    
    // create 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")
        print(error!.localizedDescription)
        return
      }
        
      // make sure we got data
      guard let responseData = data else {
        print("error: did not receive data")
        return
      }
        
      // convert Data in JSON && parse the result as JSON, since that's what the API provides
      do {
        guard let object = try JSONSerialization.jsonObject(with: responseData, options: [])
          as? [String: Any] else {
            print("error trying to convert data to JSON")
            return
        }
        //JSON Response
        guard let todoTitle = object["response"] as? NSDictionary else {
          print("Could not get todo title from JSON")
          return
        }
        
        //Get array in response
        let responseList = todoTitle.value(forKey: "radioList") as! NSArray
        
        for item in responseList {
            let dic = item as! NSDictionary
            let str = dic.value(forKey: "radio_des") as! String
            self.arrName.append(str)
            print(item)
        }
        
        DispatchQueue.main.async {
            self.tblView.reloadData()
        }
        
      } catch  {
        print("error trying to convert data to JSON")
        return
      }
    }
    task.resume()
}

Usage:

getAPICalling(mainUrl:"https://dousic.com/api/radiolist?user_id=16")

Here is the complete code for REST API requests using NSURLSession in swift

For GET Request

 let configuration = NSURLSessionConfiguration .defaultSessionConfiguration()
    let session = NSURLSession(configuration: configuration)


    let urlString = NSString(format: "your URL here")

    print("get wallet balance url string is \(urlString)")
    //let url = NSURL(string: urlString as String)
    let request : NSMutableURLRequest = NSMutableURLRequest()
    request.URL = NSURL(string: NSString(format: "%@", urlString) as String)
    request.HTTPMethod = "GET"
    request.timeoutInterval = 30

    request.addValue("application/json", forHTTPHeaderField: "Content-Type")
    request.addValue("application/json", forHTTPHeaderField: "Accept")

    let dataTask = session.dataTaskWithRequest(request) {
        (let data: NSData?, let response: NSURLResponse?, let error: NSError?) -> Void in

        // 1: Check HTTP Response for successful GET request
        guard let httpResponse = response as? NSHTTPURLResponse, receivedData = data
            else {
                print("error: not a valid http response")
                return
        }

        switch (httpResponse.statusCode)
        {
        case 200:

            let response = NSString (data: receivedData, encoding: NSUTF8StringEncoding)
            print("response is \(response)")


            do {
                let getResponse = try NSJSONSerialization.JSONObjectWithData(receivedData, options: .AllowFragments)

                EZLoadingActivity .hide()

               // }
            } catch {
                print("error serializing JSON: \(error)")
            }

            break
        case 400:

            break
        default:
            print("wallet GET request got response \(httpResponse.statusCode)")
        }
    }
    dataTask.resume()

For POST request ...

let configuration = NSURLSessionConfiguration .defaultSessionConfiguration()
    let session = NSURLSession(configuration: configuration)

    let params = ["username":bindings .objectForKey("username"), "provider":"walkingcoin", "securityQuestion":securityQuestionField.text!, "securityAnswer":securityAnswerField.text!] as Dictionary<String, AnyObject>

    let urlString = NSString(format: “your URL”);
    print("url string is \(urlString)")
    let request : NSMutableURLRequest = NSMutableURLRequest()
    request.URL = NSURL(string: NSString(format: "%@", urlString)as String)
    request.HTTPMethod = "POST"
    request.timeoutInterval = 30
    request.addValue("application/json", forHTTPHeaderField: "Content-Type")
    request.addValue("application/json", forHTTPHeaderField: "Accept")      
    request.HTTPBody  = try! NSJSONSerialization.dataWithJSONObject(params, options: [])

    let dataTask = session.dataTaskWithRequest(request)
        {
            (let data: NSData?, let response: NSURLResponse?, let error: NSError?) -> Void in
            // 1: Check HTTP Response for successful GET request
            guard let httpResponse = response as? NSHTTPURLResponse, receivedData = data
                else {
                    print("error: not a valid http response")
                    return
            }

            switch (httpResponse.statusCode)
            {
            case 200:

                let response = NSString (data: receivedData, encoding: NSUTF8StringEncoding)


                if response == "SUCCESS"
                {

                }

            default:
                print("save profile POST request got response \(httpResponse.statusCode)")
            }
    }
    dataTask.resume()

I hope it works.

Swift 3.0

let request = NSMutableURLRequest(url: NSURL(string: "http://httpstat.us/200")! as URL)
let session = URLSession.shared
request.httpMethod = "GET"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("application/json", forHTTPHeaderField: "Accept")

let task = session.dataTask(with: request as URLRequest, completionHandler: {data, response, error -> Void in
      if error != nil {
          print("Error: \(String(describing: error))")
      } else {
          print("Response: \(String(describing: response))")
      }
 })

 task.resume()

swift 4

USE ALAMOFIRE in our App plz install pod file

pod 'Alamofire', '~> 4.0'

We can Use API for Json Data -https://swapi.co/api/people/

Then We can create A networking class for Our project- networkingService.swift

import Foundation
import Alamofire
typealias JSON = [String:Any]
class networkingService{
     static let shared = networkingService()
    private init() {}
    func getPeople(success successblock: @escaping (GetPeopleResponse) -> Void)
    {
    Alamofire.request("https://swapi.co/api/people/").responseJSON { response in
        guard let json = response.result.value as? JSON else {return}
       // print(json)
        do {
                let getPeopleResponse = try GetPeopleResponse(json: json)
                successblock(getPeopleResponse)
            }catch{}
    }
    }
    func getHomeWorld(homeWorldLink:String,completion: @escaping(String) ->Void){
        Alamofire.request(homeWorldLink).responseJSON {(response) in
            guard let json = response.result.value as? JSON,
            let name = json["name"] as? String
                else{return}
            completion(name)
        }
}
}

Then Create NetworkingError.swift class

import Foundation
enum networkingError : Error{
    case badNetworkigStuff

}

Then create Person.swift class

import Foundation
struct Person {
    private let homeWorldLink : String
    let birthyear : String
    let gender : String
    let haircolor : String
    let eyecolor : String
    let height : String
    let mass : String
    let name : String
    let skincolor : String
    init?(json : JSON) {
        guard let birthyear = json["birth_year"] as? String,
        let eyecolor = json["eye_color"] as? String,
        let gender = json["gender"] as? String,
        let haircolor = json["hair_color"] as? String,
        let height = json["height"] as? String,
        let homeWorldLink = json["homeworld"] as? String,
        let mass = json["mass"] as? String,
        let name = json["name"] as? String,
        let skincolor = json["skin_color"] as? String
        else { return nil }
        self.homeWorldLink = homeWorldLink
        self.birthyear = birthyear
        self.gender = gender
        self.haircolor = haircolor
        self.eyecolor = eyecolor
        self.height = height
        self.mass = mass
        self.name = name
        self.skincolor = skincolor
    }
    func homeWorld(_ completion: @escaping (String) -> Void)  {
        networkingService.shared.getHomeWorld(homeWorldLink: homeWorldLink){ (homeWorld) in
            completion(homeWorld)
        }
    }
}

Then create DetailVC.swift

import UIKit
class DetailVC: UIViewController {
    var person :Person!
    @IBOutlet var name: UILabel!
    @IBOutlet var birthyear: UILabel!
    @IBOutlet var homeworld: UILabel!
    @IBOutlet var eyeColor: UILabel!
    @IBOutlet var skinColor: UILabel!
    @IBOutlet var gender: UILabel!
    @IBOutlet var hairColor: UILabel!
    @IBOutlet var mass: UILabel!
    @IBOutlet var height: UILabel!
    override func viewDidLoad() {
        super.viewDidLoad()
       print(person)
        name.text = person.name
        birthyear.text = person.birthyear
        eyeColor.text = person.eyecolor
        gender.text = person.gender
        hairColor.text = person.haircolor
        mass.text = person.mass
        height.text = person.height
        skinColor.text = person.skincolor
        person.homeWorld{(homeWorld) in
            self.homeworld.text = homeWorld
        }
    }
}

Then Create GetPeopleResponse.swift class

import Foundation
struct GetPeopleResponse {
    let people : [Person]
    init(json :JSON) throws {
        guard let results = json["results"] as? [JSON] else { throw networkingError.badNetworkigStuff}
        let people = results.map{Person(json: $0)}.flatMap{ $0 }
        self.people = people
        }
}

Then Our View controller class

import UIKit

class ViewController: UIViewController {

    @IBOutlet var tableVieww: UITableView!
    var people = [Person]()


    @IBAction func getAction(_ sender: Any)
    {
    print("GET")
        networkingService.shared.getPeople{ response in
            self.people = response.people
           self.tableVieww.reloadData()
        }
    }
    override func prepare(for segue: UIStoryboardSegue, sender: Any?)
    {
        guard segue.identifier == "peopleToDetails",
        let detailVC = segue.destination as? DetailVC,
        let person = sender as AnyObject as? Person
        else {return}
        detailVC.person = person
        }
}
    extension ViewController:UITableViewDataSource{
        func numberOfSections(in tableView: UITableView) -> Int {
            return 1
        }
        func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
            return people.count
        }
        func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
         let cell = UITableViewCell()
            cell.textLabel?.text = people[indexPath.row].name

            return cell

        }
    }
extension ViewController:UITableViewDelegate{
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        performSegue(withIdentifier: "peopleToDetails", sender: people[indexPath.row])
    }
}

In our StoryBoard

plz Connect with our View with another one using segue with identifier -peopleToDetails

• Use UITableView In our First View

• Use UIButton For get the Data

• Use 9 Labels in our DetailVc

let headers = [
                "cache-control": "no-cache",
                "postman-token": "6f8a-12c6-87a1-ac0f25d6385a"
            ]

            let request = NSMutableURLRequest(url: NSURL(string: "Your url string")! as URL,
                                              cachePolicy: .useProtocolCachePolicy,
                                              timeoutInterval: 10.0)
            request.httpMethod = "GET"
            request.allHTTPHeaderFields = headers

            let session = URLSession.shared
            let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
                if error == nil && data != nil {
                    do {
                        // Convert NSData to Dictionary where keys are of type String, and values are of any type
                        let json = try JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.mutableContainers) as! [String:AnyObject]
                        print(json)

                        //do your stuff

                      //  completionHandler(true)

                    } catch {
                       // completionHandler(false)
                    }
                }
                else if error != nil
                {
                    //completionHandler(false)
                }
            }).resume()
            }

Api Call using Model Class

    let urlString = "http://--.154.--.78/------/index.php?route=api/coupon/all"

    let url = URL(string: urlString)
    var request = URLRequest(url: url!)
    request.httpMethod = "GET"

    URLSession.shared.dataTask(with:request) { (data, response, error) in
        if error != nil {
            print(error)
        } else {
            do {

                let parsedDictionaryArray = try JSONSerialization.jsonObject(with: data!) as! [String:AnyObject]
                print(parsedDictionaryArray)

                if let arry = parsedDictionaryArray["data"] as? [[String:AnyObject]] {
                for dic in arry {
                    let name = dic["name"]
                    let descriptionData = dic["description"]
                    self.modelReference.append(model(name: name as! String, descriptionStr: descriptionData as! String))
                    print(name!)
                }
                }
            } catch let error as NSError {
                print(error)
            }
        }

        }.resume()

create a variable and connect with model class

var modelReference = [model]()

create a model class New -> swift class

import Foundation
class model : NSObject{
var name : String
var descriptionStr: String

init(name : String, descriptionStr: String)
{
    self.name = name
    self.descriptionStr = descriptionStr
}

}

then we can connect with our table view objects

let cell = tableView.dequeueReusableCell(withIdentifier: "TableViewCellID")as! TableViewCell
    cell.listName.text = modelReference[indexPath.row].name

If you're working in Swift 3, the syntax changes. The example here worked for me and has a good explanation of the steps: https://grokswift.com/simple-rest-with-swift/

This is the code from that tutorial:

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)

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()

edited for swift 2

let url = NSURL(string: "http://www.test.com")

    let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
        print(NSString(data: data!, encoding: NSUTF8StringEncoding))
    }

    task.resume()

Swift 4 - GET request

var request = URLRequest(url: URL(string: "http://example.com/api/v1/example")!)
request.httpMethod = "GET"

URLSession.shared.dataTask(with: request, completionHandler: { data, response, error -> Void in
    do {
        let jsonDecoder = JSONDecoder()
        let responseModel = try jsonDecoder.decode(CustomDtoClass.self, from: data!)
        print(responseModel)
    } catch {
        print("JSON Serialization error")
    }
}).resume()

Don't forget to configure App Transport Security Settings to add your domain to the exceptions and allow insecure http requests if you're hitting endpoints without using HTTPS.

You can use a tool like http://www.json4swift.com/ to autogenerate your Codeable Mappings from your JSON responses.

In swift 3.3 and 4. I crated APIManager class with two public methods. Just pass required parameter, api name and request type. You will get response then pass it to the closure.

 import UIKit   

    struct RequestType {
      static let  POST = "POST"
      static let  GET = "GET"
    }

    enum HtttpType: String {
      case POST = "POST"
      case GET  = "GET"
    }

    class APIManager: NSObject {


      static let sharedInstance: APIManager = {

        let instance = APIManager()
        return instance
      }()
     private init() {}
        // First Method

          public func requestApiWithDictParam(dictParam: Dictionary<String,Any>, apiName: String,requestType: String, isAddCookie: Bool, completionHendler:@escaping (_ response:Dictionary<String,AnyObject>?, _ error: NSError?, _ success: Bool)-> Void) {

            var apiUrl = “” // Your api url
            apiUrl =  apiUrl.appendingFormat("%@", apiName)
            let config = URLSessionConfiguration.default
            let session = URLSession(configuration: config)
            let url = URL(string: apiUrl)!
            let HTTPHeaderField_ContentType  = "Content-Type"
            let ContentType_ApplicationJson  = "application/json"
            var request = URLRequest.init(url: url)

            request.timeoutInterval = 60.0
            request.cachePolicy = URLRequest.CachePolicy.reloadIgnoringLocalCacheData
            request.addValue(ContentType_ApplicationJson, forHTTPHeaderField: HTTPHeaderField_ContentType)
            request.httpMethod = requestType

            print(apiUrl)
            print(dictParam)

            let dataTask = session.dataTask(with: request) { (data, response, error) in

              if error != nil   {
                completionHendler(nil, error as NSError?, false)
              } do {
                let resultJson = try JSONSerialization.jsonObject(with: data!, options: []) as? [String:AnyObject]
                print("Request API = ", apiUrl)
                print("API Response = ",resultJson ?? "")
                completionHendler(resultJson, nil, true)

              } catch {
                completionHendler(nil, error as NSError?, false)
              }
            }
            dataTask.resume()
          }

           // Second Method
           public func requestApiWithUrlString(param: String, apiName: String,requestType: String, isAddCookie: Bool, completionHendler:@escaping (_ response:Dictionary<String,AnyObject>?, _ error: NSError?, _ success: Bool)-> Void ) {
                var apiUrl = "" // Your api url
                let config = URLSessionConfiguration.default
                let session = URLSession(configuration: config)            
                var request: URLRequest?

                if requestType == "GET" {

                  apiUrl =  String(format: "%@%@&%@", YourAppBaseUrl,apiName,param)
                  apiUrl = apiUrl.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed)!
                  print("URL=",apiUrl)

                  let url = URL(string: apiUrl)!
                  request = URLRequest.init(url: url)
                  request?.httpMethod = "GET"

                } else {

                  apiUrl =  String(format: "%@%@", YourAppBaseUrl,apiName)
                  apiUrl = apiUrl.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed)!
                  print("URL=",apiUrl)

                  let bodyParameterData = param.data(using: .utf8)
                  let url = URL(string: apiUrl)!

                  request = URLRequest(url: url)
                  request?.httpBody = bodyParameterData
                  request?.httpMethod = "POST"
                }

                request?.timeoutInterval = 60.0
                request?.cachePolicy = URLRequest.CachePolicy.reloadIgnoringLocalCacheData
                request?.httpShouldHandleCookies = true

                let dataTask = session.dataTask(with: request!) { (data, response, error) in

                  if error != nil {
                    completionHendler(nil, error as NSError?, false)
                  } do {
                    if data != nil  {
                      let resultJson = try JSONSerialization.jsonObject(with: data!, options: []) as? [String:AnyObject]

                      print("Request API = ", apiUrl)
                      print("API Response = ",resultJson ?? "")
                      completionHendler(resultJson, nil, true) 
                    } else  {
                      completionHendler(nil, error as NSError?, false)
                    }
                  } catch {
                    completionHendler(nil, error as NSError?, false)
                  }
                }
                dataTask.resume()
              }
    }

    // Here is example of calling Post API from any class

     let bodyParameters = String(format: "appid=%@&appversion=%@","1","1")
            APIManager.sharedInstance.requestApiWithUrlString(param: bodyParameters, apiName: "PASS_API_NAME", requestType: HtttpType.POST.rawValue, isAddCookie: false) { (dictResponse, error, success) in

                if success {
                    if let dictMessage = dictResponse?["message"] as? Dictionary<String, AnyObject> {
                // do you work
                    }

                }  else {
                    print("Something went wrong...")
                }
            }
        }


/// Or just use simple function 

func dataRequest() {
    let urlToRequest = "" // Your API url

    let url = URL(string: urlToRequest)!
    let session4 = URLSession.shared
    let request = NSMutableURLRequest(url: url)
    request.httpMethod = "POST"
    request.cachePolicy = NSURLRequest.CachePolicy.reloadIgnoringCacheData
    let paramString = "data=Hello"
    request.httpBody = paramString.data(using: String.Encoding.utf8)
    let task = session4.dataTask(with: request as URLRequest) { (data, response, error) in
      guard let _: Data = data, let _: URLResponse = response, error == nil else {
        print("*****error")
        return
      }
      if let dataString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue) {
          print("****Data: \(dataString)") //JSONSerialization
      }
    }
    task.resume()
  }

Swift 5

API call method

//Send Request with ResultType<Success, Error>
    func fetch(requestURL:URL,requestType:String,parameter:[String:AnyObject]?,completion:@escaping (Result<Any>) -> () ){
        //Check internet connection as per your convenience
        //Check URL whitespace validation as per your convenience
        //Show Hud
        var urlRequest = URLRequest.init(url: requestURL)
        urlRequest.cachePolicy = .reloadIgnoringLocalCacheData
        urlRequest.timeoutInterval = 60
        urlRequest.httpMethod = String(describing: requestType)
        urlRequest.setValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")
        urlRequest.setValue("application/json; charset=utf-8", forHTTPHeaderField: "Accept")
        
        //Post URL parameters set as URL body
        if let params = parameter{
            do{
                let parameterData = try JSONSerialization.data(withJSONObject:params, options:.prettyPrinted)
                urlRequest.httpBody = parameterData
            }catch{
               //Hide hude and return error
                completion(.failure(error))
            }
        }
        //URL Task to get data
        URLSession.shared.dataTask(with: requestURL) { (data, response, error) in
            //Hide Hud
            //fail completion for Error
            if let objError = error{
                completion(.failure(objError))
            }
            //Validate for blank data and URL response status code
            if let objData = data,let objURLResponse = response as? HTTPURLResponse{
                //We have data validate for JSON and convert in JSON
                do{
                    let objResposeJSON = try JSONSerialization.jsonObject(with: objData, options: .mutableContainers)
                    //Check for valid status code 200 else fail with error
                    if objURLResponse.statusCode == 200{
                        completion(.success(objResposeJSON))
                    }
                }catch{
                    completion(.failure(error))
                }
            }
        }.resume()
    }

Use of API call method

func useOfAPIRequest(){
        if let baseGETURL = URL(string:"https://postman-echo.com/get?foo1=bar1&foo2=bar2"){
            self.fetch(requestURL: baseGETURL, requestType: "GET", parameter: nil) { (result) in
                      switch result{
                      case .success(let response) :
                        print("Hello World \(response)")
                      case .failure(let error) :
                        print("Hello World \(error)")
                          
                      }
                  }
        }
      
    }

Swift 5 & 4

let params = ["username":"john", "password":"123456"] as Dictionary<String, String>

var request = URLRequest(url: URL(string: "http://localhost:8080/api/1/login")!)
request.httpMethod = "POST"
request.httpBody = try? JSONSerialization.data(withJSONObject: params, options: [])
request.addValue("application/json", forHTTPHeaderField: "Content-Type")

let session = URLSession.shared
let task = session.dataTask(with: request, completionHandler: { data, response, error -> Void in
    print(response!)
    do {
        let json = try JSONSerialization.jsonObject(with: data!) as! Dictionary<String, AnyObject>
        print(json)
    } catch {
        print("error")
    }
})

task.resume()

I think the NSURLSession api fits better in this situation. Because if you write swift code your project target is at least iOS 7 and iOS 7 supports NSURLSession api. Anyway here is the code

let url = "YOUR_URL"

NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: url)) { data, response, error in
    // Handle result
}.resume()