ios - 在 iOS Swift 中使用委托(delegate)和协议(protocol)从 dataTaskWithRequest 返回数据

Question

我有一个框架，它调用一个 API，该 API 将 JSON 返回给我。问题是我的 SDK 中有一个函数，它使用 NSURLSession 并调用 DataTaskWithRequest 来获取数据。问题是我的函数甚至在正确获取数据之前就返回了值。我尝试将 Completion Handler 与 DataTaskWithRequest 结合使用，目前使用 while 循环来等待接收数据。还有其他可能的方法吗

代码

public func getDetails() -> AnyObject {
    if Reachability.isConnectedToNetwork()
    {
        received = false
        let baseUrl = "API_URL  Here"
        let url = NSURL(string: baseUrl)
        let request = NSURLRequest(URL: url!)
        let session = NSURLSession.sharedSession()

        print("Starting the connection")
        let task = session.dataTaskWithRequest(request, completionHandler : {
            (data, response, error ) in

            //Proper JSON Form

            do
            {
                self.JSON = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments)
            }
            catch
            {
                print("Error")
                return
            }

            self.received = true

        })
        task.resume()

        print("Going through the loop")
        while(!received)
        {
            print("Searching")
        }
        print(JSON)
            return JSON
    }
    else
    {

        let alert = UIAlertView(title: "No Internet Connection", message: "Make sure your device is connected to the internet.", delegate: nil, cancelButtonTitle: "OK")
        alert.show()
        return 0

    }
}

Answer 1

你的问题是你试图将异步的东西变成同步的东西。用伪代码总结一下，您正在这样做:-

let myData = getDetails(blah)
doSomeAction(myData)

处理它的方法是使用完成 block 作为指示器本身并使所有内容异步。此代码尚未经过测试

public typealias CompletionHandler = (success: Bool, message: String, json: JSON?, error: NSError?) -> Void

func getDetailsAsync(completion: CompletionHandler) {
    if Reachability.isConnectedToNetwork()
    {
        received = false
        let baseUrl = "API_URL  Here"
        let url = NSURL(string: baseUrl)
        let request = NSURLRequest(URL: url!)
        let session = NSURLSession.sharedSession()

        print("Starting the connection")
        let task = session.dataTaskWithRequest(request, completionHandler : {
            (data, response, error ) in

            //Proper JSON Form
            if error != nil {
                completion(false, "error", nil, error)
            }
            else {
                do
                {
                    self.JSON = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments)
                    completion(true, "OK", self.JSON, nil)
                }
                catch
                {
                    print("Error")
                    completion(false, "JSON parsing failed", nil, nil)
                }
            }

        })
        task.resume()
    }
    else {
        completion(false, "No network", nil, nil)
    }
}

这样调用它:

getDetailsAsync() {
    (success, message, json, error) in 
    if success == true {
        print(json)

    }
    else {
        // Do your alert here
        print(message)
        print(error)
    }
}

This答案可能会有所帮助。