Swift 等到 dataTaskWithRequest 完成调用 return

Question

我是 Swift 的新手，我有一个关于同步调用的问题。我想同步调用 dataTaskWithRequest，以便在 dataTaskWithRequest 完成后调用 return 方法。这是我的代码：

private func sendRequest (request: NSURLRequest) -> NSData{
    let session = NSURLSession.sharedSession()
    var dataReceived: NSData = NSData ()
    let task = session.dataTaskWithRequest(request) { data, response, error in
        if error != nil{
            print("Error -> \(error)")
            return
        }
    dataReceived = data!
    }
    task.resume()
    return dataReceived
}

最好的方法是什么？我试过使用完成处理程序，但我做不到。

非常感谢您的帮助。

Answer 1

完成是 swift 中正确和最好的方法！

  func sendRequest (request: NSURLRequest,completion:(NSData?)->()){

    NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
        if error != nil{
            return completion(data)
        }else{
            return completion(nil)
        }
    }.resume()
}

并调用：

  sendRequest( yourRequest ) { data in
        if let data = data {
             // do something
        }
   }}

Answer 2

执行此操作的最佳方法是回调函数。

private func sendRequest (request: NSURLRequest, callback: (data: NSData) -> () {
    let session = NSURLSession.sharedSession()
    var dataReceived: NSData = NSData ()
    let task = session.dataTaskWithRequest(request) { data, response, error in
        if error != nil{
            print("Error -> \(error)")
            return
        }
        callback(data!)
    }
    task.resume()
}

你可以这样调用这个函数

self.sendRequest(request, { (data) in 
    //data is the data you get from the request
}

Answer 3

您可以像这样将异步调用与信号量同步：

private func sendRequest(request: NSURLRequest) -> NSData? {
    let session = NSURLSession.sharedSession()
    var dataReceived: NSData?
    let sem = dispatch_semaphore_create(0)

    let task = session.dataTaskWithRequest(request) { data, response, error in
        defer { dispatch_semaphore_signal(sem) }

        if let error = error {
            print("Error -> \(error)")
            return
        }

        dataReceived = data
    }

    task.resume()

    // This line will wait until the semaphore has been signaled
    // which will be once the data task has completed
    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER)
    return dataReceived
}

然后你像这样使用函数：

let url = NSURL(string: "http://www.google.com")!
let req = NSURLRequest(URL: url)
let data = sendRequest(req)
print("This is data: \(data)")

对于Swift5 原理是一样的，只是有些项目改名了。请注意，这还会显示请求的更多设置。

static func sendRequest() -> Data? {
  let session = URLSession.shared
  var dataReceived: Data?
  let sem = DispatchSemaphore.init(value: 0)

  let params = ["key" : "value"] as Dictionary<String, String>
  let token = ""

  var body = try? JSONSerialization.data(withJSONObject: params, options: [])

  var request = URLRequest(url: URL(string: "https://example.com")!)
  request.httpMethod = "POST"
  request.httpBody = body
  request.addValue("application/json", forHTTPHeaderField: "Content-Type")
  request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")

    let task = session.dataTask(with: request) { data, response, error in
        defer { sem.signal() }

        if let error = error {
            print("Error -> \(error)")
            return
        }


        dataReceived = data
    }

  task.resume()

  // This line will wait until the semaphore has been signaled
  // which will be once the data task has completed
  sem.wait()

  return dataReceived
}

使用它

let data = sendRequest()

Swift 等到 dataTaskWithRequest 完成调用 return

Swift wait until dataTaskWithRequest has finished to call the return

swift

nsurlconnection

nsurlsession

synchronous