Question

使用XCode-8.2.1，Swift-3.0.2和iOS-10.2.1，

我正在尝试调用两个不同的URLSession.shared.dataTasks（第一个是简单的URL请求，第二个是POST请求）。

由于我的第一个dataTask提供了第二个dataTask的httpBody所需的结果，因此两个URLSession.shared.dataTasks将一个接一个地串行运行！（以及准备代码应连续运行）。

到目前为止，我尝试使用两个连续的serialQueue.sync{}个队列。但我必须意识到代码没有按照我想要的顺序执行。

日志中的print语句结果如下：

Hmmmmmm 2
Hmmmmmm 1
Hmmmmmm 3

（根据需要代替1,2,3）！

如何获得订单1,2,3

（即如何确保第二个dataTask的httpBody可以填充来自第一个dataTask的结果？）

这是我的代码:(不可执行，因为网址已被删除 - 但您明白了这一点）！

import UIKit

class ViewController: UIViewController {

    let serialQueue = DispatchQueue(label: "myResourceQueue")
    var stationID: Int = 0

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.


        self.serialQueue.sync {
            let myResourceURL = URL(string: "myQueryString1")
            let task = URLSession.shared.dataTask(with: myResourceURL!) { (data, response, error) in
                if (error != nil) {
                    // print(error.debugDescription)
                } else {
                    if let myData = data {
                        do {
                            let myJson = try JSONSerialization.jsonObject(with: myData, options: JSONSerialization.ReadingOptions.mutableContainers) as AnyObject
                            // print(myJson)
                            // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                            print("Hmmmmmm 1")
                            // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                        } catch {
                            // error
                        }
                    }
                }
            }
            task.resume()
        }
        self.serialQueue.sync {
            var request = URLRequest(url: URL(string: "myQueryString2")!)
            request.httpMethod = "POST"
            request.addValue("API_id", forHTTPHeaderField: "Authorization")
            request.addValue("application/xml", forHTTPHeaderField: "Content-Type")
            // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
            print("Hmmmmmm 2")
            // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
            let postString: String = "My_XML_POST_Body"
            request.httpBody = postString.data(using: .utf8)
            let task = URLSession.shared.dataTask(with: request) { data, response, error in
                // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                print("Hmmmmmm 3")
                // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
            }
            task.resume()
        }
    }

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

任何帮助表示赞赏！

Answer 1

我终于找到了解决方案：

受到this answer的启发，我引入了URLSessionDataDelegate及其委托回调方法（即didReceive response:，didReceive data:和didCompleteWithError error:。

重要提示：您需要使用委托设置URLSession，以使引入的URLSessionDelegate的回调方法有效：使用URLSession（配置：....），如下所示：

let URLSessionConfig = URLSessionConfiguration.default
let session = URLSession(configuration: URLSessionConfig, delegate: self, delegateQueue: OperationQueue.main)

在那之后，你很高兴，即现在正如预期的那样：

Hmmmmmm 1
Hmmmmmm 2
Hmmmmmm 3

这是最终的代码（再次不能执行，因为URL已被取出 - 但你明白了这一点）！

import UIKit

class ViewController: UIViewController, URLSessionDataDelegate {

    var stationID: Int = 0
    let URLSessionConfig = URLSessionConfiguration.default
    var session: URLSession?
    var task1: URLSessionTask?
    var task2: URLSessionTask?

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        self.session = URLSession(configuration: URLSessionConfig, delegate: self, delegateQueue: OperationQueue.main)

        // prepare dataTask Nr 1
        let myResourceURL = URL(string: "myQueryString1")
        self.task1 = session?.dataTask(with: myResourceURL!)

        // start dataTask Nr 1 (URL-request)
        self.task1?.resume()
    }

    // Optional: Use this method if you want to get a response-size information 
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {

        // print(Int(response.expectedContentLength))
        completionHandler(URLSession.ResponseDisposition.allow)
    }

    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {

        if dataTask == self.task1 {
           do {
              let myJson = try JSONSerialization.jsonObject(with: myData, options: JSONSerialization.ReadingOptions.mutableContainers) as AnyObject
              // print(myJson)
              // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
              print("Hmmmmmm 1")
              // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

              // prepare dataTask Nr 2
              self.task2 = self.session?.dataTask(with: self.prepareMyURLRequest())
           } catch {
              // error
           }
        } else if dataTask == self.task2 {

            // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
            print("Hmmmmmm 3")
            // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

        } else {
            print("unknown dataTask callback")
        }
    }

    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
       if (error != nil) {
          // print(error.debugDescription)
       } else if task == self.task1 {

          // start dataTask Nr 2 (POST URL-request)
          self.task2?.resume()
       }
    }

    func prepareMyURLRequest() -> URLRequest {
        var request = URLRequest(url: URL(string: "myQueryString2")!)
        request.httpMethod = "POST"
        request.addValue("API_id", forHTTPHeaderField: "Authorization")
        request.addValue("application/xml", forHTTPHeaderField: "Content-Type")
        // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        print("Hmmmmmm 2")
        // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        let postString: String = "My_XML_POST_Body"
        request.httpBody = postString.data(using: .utf8)
        return request
    }

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

}

Answer 2

如果task2需要task1的结果，你应该从task1

的完成块启动task2

URLSession.shared.dataTask(with: request) { data, response, error in
    // process task1 and setup request2
    URLSession.shared.dataTask(with: request2) { data, response, error in
        // process task2
    }.resume()
}.resume()

当然，对于多个请求，这会有点笨拙，所以最好使用Promises＆amp;期货。 Promise＆amp;有几种实现方式。 Swift的期货，例如Promis

如何为URLSession任务同步串行队列？

2 个答案: