Swift：如何在异步urlsession函数中返回值？

Question

如您所见，我正在接收一个JSON文件，使用SwiftyJSON对其进行解析，并尝试返回totalTime，但是它不允许我这样做。我该怎么做呢？func googleDuration(origin: String, destination: String) -> Int{    // do calculations origin and destiantion with google distance matrix api    let originFix = origin.stringByReplacingOccurrencesOfString(" ", withString: "+", options: NSStringCompareOptions.LiteralSearch, range: nil);    let destinationFix = destination.stringByReplacingOccurrencesOfString(" ", withString: "+", options: NSStringCompareOptions.LiteralSearch, range: nil);    let urlAsString = "https://maps.googleapis.com/maps/api/distancematrix/json?origins="+originFix+"&destinations="+destinationFix;    println(urlAsString);    let url = NSURL(string: urlAsString)!    let urlSession = NSURLSession.sharedSession()    let task = urlSession.dataTaskWithURL(url, completionHandler: {data, response, error -> Void in        if error != nil {            // If there is an error in the web request, print it to the console            println(error.localizedDescription)        }        println("parsing JSON");        let json = JSON(data: data);        if (json["status"].stringValue == "OK") {            if let totalTime = json["rows"][0]["elements"][0]["duration"]["value"].integerValue {                println(totalTime);            }        }    })    task.resume();}

Answer 1

另一个例子：

func getJason(url: NSURL, completionHandler: (String?, NSError?) -> Void ) -> NSURLSessionTask {

    var finalData: String!

    let task = NSURLSession.sharedSession().dataTaskWithURL(url) { (data, response, error) -> Void in

        if error != nil{

            completionHandler(nil, error)

            return

        }

        else{

        if let urlContent = data{

            do{

                let jsonData = try NSJSONSerialization.JSONObjectWithData(urlContent, options: NSJSONReadingOptions.MutableContainers)

                if let ip = jsonData["ip"]{

                    finalData = ip as? String

                    completionHandler(finalData, nil)

                    return

                }

            }catch{

                print("EMPTY")

            }

        }

    }

}

    task.resume()

    return task

}

然后我在viewDidLoad中调用了它

getJason(url) { (ipAddress, error) -> Void in

        if error != nil{

            print(error)

        }

        else{

            if let ip = ipAddress{          //To get rid of optional

        self.ipLabelDisplay.text = "Your Ip Address is: \(ip)"

            }

        }

    }