你可以使用URL URLRequest URLSession或者NSURLConnection就像你在Objective-C中通常做的那样。注意，对于iOS 7.0及更高版本，URLSession是首选。

使用URLSession

初始化URL对象和URLSession中的URLSessionDataTask。然后使用resume()运行任务。

let url = URL(string: "http://www.stackoverflow.com")!

let task = URLSession.shared.dataTask(with: url) {(data, response, error) in
    guard let data = data else { return }
    print(String(data: data, encoding: .utf8)!)
}

task.resume()

使用NSURLConnection

首先，初始化URL和URLRequest:

let url = URL(string: "http://www.stackoverflow.com")!
var request = URLRequest(url: url)
request.httpMethod = "POST" 

然后，你可以异步加载请求:

NSURLConnection.sendAsynchronousRequest(request, queue: OperationQueue.main) {(response, data, error) in
    guard let data = data else { return }
    print(String(data: data, encoding: .utf8)!)
}

或者你可以初始化一个NSURLConnection:

let connection = NSURLConnection(request: request, delegate:nil, startImmediately: true)

只是要确保将委托设置为nil以外的东西，并使用委托方法处理接收到的响应和数据。

要了解更多细节，请查看NSURLConnectionDataDelegate协议的文档

在Xcode操场上测试

如果你想在Xcode游乐场上尝试这段代码，添加import PlaygroundSupport到你的游乐场，以及下面的调用:

PlaygroundPage.current.needsIndefiniteExecution = true

这将允许你在操场上使用异步代码。

斯威夫特3.0

通过一个小抽象 https://github.com/daltoniam/swiftHTTP

例子

    do {
        let opt = try HTTP.GET("https://google.com")
        opt.start { response in
            if let err = response.error {
                print("error: \(err.localizedDescription)")
                return //also notify app of failure as needed
            }
            print("opt finished: \(response.description)")
            //print("data is: \(response.data)") access the response of the data with response.data
        }
    } catch let error {
        print("got an error creating the request: \(error)")
    }

//这是一个对我有用的例子

//发送请求到服务器的Swift函数

func insertRecords()
{



    let usrID = txtID.text
    let checkin = lblInOut.text
    let comment = txtComment.text



    // The address of the web service
    let urlString = "http://your_url/checkInOut_post.php"

    // These are the keys that your are sending as part of the post request
    let keyValues = "id=\(usrID)&inout=\(checkin)&comment=\(comment)"




    // 1 - Create the session by getting the configuration and then
    //     creating the session

    let config = NSURLSessionConfiguration.defaultSessionConfiguration()
    let session = NSURLSession(configuration: config, delegate: nil, delegateQueue: nil)


    // 2 - Create the URL Object

    if let url = NSURL(string: urlString){


        // 3 - Create the Request Object

        var request  = NSMutableURLRequest(URL: url)
        request.HTTPMethod = "POST"

        // set the key values
        request.HTTPBody = keyValues.dataUsingEncoding(NSUTF8StringEncoding);


        // 4 - execute the request

        let taskData = session.dataTaskWithRequest(request, completionHandler: {

            (data:NSData!, response:NSURLResponse!, error:NSError!) -> Void in

            println("\(data)")

            // 5 - Do something with the Data back

            if (data != nil) {

                // we got some data back
                println("\(data)")

                let result = NSString(data: data , encoding: NSUTF8StringEncoding)
                println("\(result)")

                if result == "OK" {

                    let a = UIAlertView(title: "OK", message: "Attendece has been recorded", delegate: nil, cancelButtonTitle: "OK")

                    println("\(result)")

                    dispatch_async(dispatch_get_main_queue()) {


                    a.show()


                    }


                } else {
                  // display error and do something else

                }


            } else

            {   // we got an error
                println("Error getting stores :\(error.localizedDescription)")

            }


        })

        taskData.resume()



    }


}

PHP代码来获取键值

$empID = $_POST['id'];

$inOut = $_POST['inout'];

$comment = $_POST['comment'];

我调用json登录按钮点击

@IBAction func loginClicked(sender : AnyObject) {

    var request = NSMutableURLRequest(URL: NSURL(string: kLoginURL)) // Here, kLogin contains the Login API.

    var session = NSURLSession.sharedSession()

    request.HTTPMethod = "POST"

    var err: NSError?
    request.HTTPBody = NSJSONSerialization.dataWithJSONObject(self.criteriaDic(), options: nil, error: &err) // This Line fills the web service with required parameters.
    request.addValue("application/json", forHTTPHeaderField: "Content-Type")
    request.addValue("application/json", forHTTPHeaderField: "Accept")

    var task = session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
        var strData = NSString(data: data, encoding: NSUTF8StringEncoding)
        var err1: NSError?
        var json2 = NSJSONSerialization.JSONObjectWithData(strData.dataUsingEncoding(NSUTF8StringEncoding), options: .MutableLeaves, error:&err1 ) as NSDictionary

        println("json2 :\(json2)")

        if(err) {
            println(err!.localizedDescription)
        }
        else {
            var success = json2["success"] as? Int
            println("Success: \(success)")
        }
    })

    task.resume()
}

在这里，我为参数创建了一个单独的字典。

var params = ["format":"json", "MobileType":"IOS","MIN":"f8d16d98ad12acdbbe1de647414495ec","UserName":emailTxtField.text,"PWD":passwordTxtField.text,"SigninVia":"SH"]as NSDictionary
    return params
}

// You can add your own sets of parameter here.

一个简单的Swift 2.0方法来发出HTTP GET请求

HTTP请求是异步的，因此需要一种方法从HTTP请求中获取返回值。这种方法使用通知器，分布在两个类中。

示例是使用网站http://www.example.com/handler.php?do=CheckUserJson&json=检查标识符令牌的用户名和密码，该文件名为handler.php，并且在do参数上有一个switch语句以获得RESTful方法。

在viewDidLoad中，我们设置了NotifierObserver，设置了json，并调用getHTTPRequest函数。它将返回函数checkedUsernameAndPassword和从http请求返回的参数。

override func viewDidLoad() {
    super.viewDidLoad()
    // setup the Notification observer to catch the result of check username and password
    NSNotificationCenter.defaultCenter().addObserver(self, selector: "checkedUsernameAndPassword:", name: CHECK_USERNAME_AND_PASSWORD, object: nil)        
    let username = GlobalVariables.USER_NAME
    let password = GlobalVariables.PASSWORD
    // check username and password
    if let jsonString = Utility.checkUsernameAndPasswordJson(username, password:password){
        print("json string returned = \(jsonString)")
        let url = CHECKUSERJSON+jsonString
        // CHECKUSERJSON = http://www.example.com/handler.php?do=CheckUserJson&json=
        // jsonString = {\"username\":\"demo\",\"password\":\"demo\"}"
        // the php script handles a json request and returns a string identifier           
        Utility.getHTTPRequest(url,notifierId: CHECK_USERNAME_AND_PASSWORD)
        // the returned identifier is sent to the checkedUsernaeAndPassword function when it becomes availabel.
    }
}

在Utility.swift中有两个静态函数，首先用于编码json，然后执行HTTP调用。

    static func checkUsernameAndPasswordJson(username: String, password: String) -> String?{
    let para:NSMutableDictionary = NSMutableDictionary()
        para.setValue("demo", forKey: "username")
        para.setValue("demo", forKey: "password")
    let jsonData: NSData
    do{
        jsonData = try NSJSONSerialization.dataWithJSONObject(para, options: NSJSONWritingOptions())
        let jsonString = NSString(data: jsonData, encoding: NSUTF8StringEncoding) as! String
        return jsonString
    } catch _ {
        print ("UH OOO")
        return nil
    }
}

和Http请求

    static func getHTTPRequest (url:String , notifierId: String) -> Void{
    let urlString = url
    let config = NSURLSessionConfiguration.defaultSessionConfiguration()
    let session = NSURLSession(configuration: config, delegate: nil, delegateQueue: nil)
    let safeURL = urlString.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLQueryAllowedCharacterSet())!
    if let url = NSURL(string: safeURL){
        let request  = NSMutableURLRequest(URL: url)
        request.HTTPMethod = "GET"
        request.timeoutInterval = 60
        let taskData = session.dataTaskWithRequest(request, completionHandler: {
            (data:NSData?, response:NSURLResponse?, error:NSError?) -> Void in
            if (data != nil) {
                let result = NSString(data: data! , encoding: NSUTF8StringEncoding)
                sendNotification (notifierId, message: String(result), num: 0)
            }else{
                  sendNotification (notifierId, message: String(UTF8String: nil), num: -1)                    }
        })
    taskData.resume()
    }else{
        print("bad urlString = \(urlString)")
    }
}

sendNotification函数完成了循环。注意，在观察者中，在选择器字符串的末尾有一个“:”。这允许通知在userInfo中携带有效负载。我给它一个String和Int。

    static func sendNotification (key: String, message:String?, num: Int?){
    NSNotificationCenter.defaultCenter().postNotificationName(
        key,
        object: nil,
        userInfo:   (["message": message!,
                      "num": "\(num!)"])
    )
}

注意，使用HTTP是老式的，更喜欢HTTPS见我如何加载一个HTTP URL与应用程序传输安全启用在iOS 9?

Swift 4及以上:使用URLSession API进行数据请求

   // create the url
   let url = URL(string: "https://jsonplaceholder.typicode.com/todos/1")! //change the url
        
   // create the session object 
   let session = URLSession.shared
        
   // now create the URLRequest object using the url object
   let request = URLRequest(url: url)
        
   // create dataTask using the session object to send data to the server
   let task = session.dataTask(with: request as URLRequest, completionHandler: { data, response, error in
            
       guard error == nil else {
           return
       }
            
       guard let data = data else {
           return
       }
            
      do {
         //create json object from data
         if let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as? [String: Any] {
            print(json)
         }
      } catch let error {
        print(error.localizedDescription)
      }
   })

   task.resume()

Swift 4及以上，可解码和结果enum

// APIError enum which shows all possible Network errors
enum APIError: Error {
    case networkError(Error)
    case dataNotFound
    case jsonParsingError(Error)
    case invalidStatusCode(Int)
    case badURL(String)
}

// Result enum to show success or failure
enum Result<T> {
    case success(T)
    case failure(AppError)
}

// dataRequest which sends request to given URL and convert to Decodable Object
func dataRequest<T: Decodable>(with url: String, objectType: T.Type, completion: @escaping (Result<T>) -> Void) {
    
    // create the url with NSURL
    guard let dataURL = URL(string: url) else {
       completion(.failure(APIError.badURL(url))
       return
    }
    
    // create the session object
    let session = URLSession.shared
    
    // now create the URLRequest object using the url object
    let request = URLRequest(url: dataURL, cachePolicy: .useProtocolCachePolicy, timeoutInterval: 60)
    
    // create dataTask using the session object to send data to the server
    let task = session.dataTask(with: request, completionHandler: { data, response, error in
        
        guard error == nil else {
            completion(Result.failure(APIError.networkError(error!)))
            return
        }
        
        guard let data = data else {
            completion(Result.failure(AppError.dataNotFound))
            return
        }
        
        do {
            // create decodable object from data
            let decodedObject = try JSONDecoder().decode(objectType.self, from: data)
            completion(Result.success(decodedObject))
        } catch let error {
            completion(Result.failure(APIError.jsonParsingError(error as! DecodingError)))
        }
    })
    
    task.resume()
}

例子:

//如果我们想从占位符API获取todo，那么我们定义todo结构体并调用dataRequest并传递“https://jsonplaceholder.typicode.com/todos/1”字符串url。

struct ToDo: Decodable {
    let id: Int
    let userId: Int
    let title: String
    let completed: Bool
    
}

dataRequest(with: "https://jsonplaceholder.typicode.com/todos/1", objectType: ToDo.self) { (result: Result) in
    switch result {
    case .success(let object):
        print(object)
    case .failure(let error):
        print(error)
    }
}

//输出结果:

ToDo(id: 1, userId: 1, title: "delectus aut autem", completed: false)