Json Swift：如何在异步urlsession函数中返回值？

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，但它不允许我这样做。我该怎么做

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();
}

---

您应该添加自己的

completionHandler

closure参数，并在任务完成时调用它：

func googleDuration(origin: String, destination: String, completionHandler: (Int?, NSError?) -> Void ) -> NSURLSessionTask {
    // 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) { 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)
            completionHandler(nil, error)
            return
        }

        //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);
                completionHandler(totalTime, nil)
                return
            }
            let totalTimeError = NSError(domain: kAppDomain, code: kTotalTimeError, userInfo: nil) // populate this any way you prefer
            completionHandler(nil, totalTimeError)
        }
        let jsonError = NSError(domain: kAppDomain, code: kJsonError, userInfo: nil) // again, populate this as you prefer
        completionHandler(nil, jsonError)
    }
    task.resume()
    return task
}

如果调用者希望能够取消任务，我还需要返回

NSURLSessionTask

不管怎样，你可以这样称呼它：

googleDuration(origin, destination: destination) { totalTime, error in
    if let totalTime = totalTime {
        // use totalTime here
    } else {
        // handle error     
    }
}

另一个例子：

   class func getExchangeRate(#baseCurrency: String, foreignCurrency:String, completion: ((result:Double?) -> Void)!){
    let baseURL = kAPIEndPoint
    let query = String(baseCurrency)+"_"+String(foreignCurrency)

    var finalExchangeRate = 0.0
    if let url = NSURL(string: baseURL + query) {
        NSURLSession.sharedSession().dataTaskWithURL(url) { data, response, error in

            if ((data) != nil) {
                let jsonDictionary:NSDictionary = NSJSONSerialization.JSONObjectWithData(data!, options: nil, error: nil) as NSDictionary

                if let results = jsonDictionary["results"] as? NSDictionary{
                    if let queryResults = results[query] as? NSDictionary{
                        if let exchangeRate = queryResults["val"] as? Double{
                            let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
                            dispatch_async(dispatch_get_global_queue(priority, 0)) {
                                dispatch_async(dispatch_get_main_queue()) {
                                    completion(result: exchangeRate)
                                }
                            }

                        }
                    }
                }
            }
            else {
                completion(result: nil)
            }

        }.resume()
    }
}

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
}

电话：

另一个例子：

   class func getExchangeRate(#baseCurrency: String, foreignCurrency:String, completion: ((result:Double?) -> Void)!){
    let baseURL = kAPIEndPoint
    let query = String(baseCurrency)+"_"+String(foreignCurrency)

    var finalExchangeRate = 0.0
    if let url = NSURL(string: baseURL + query) {
        NSURLSession.sharedSession().dataTaskWithURL(url) { data, response, error in

            if ((data) != nil) {
                let jsonDictionary:NSDictionary = NSJSONSerialization.JSONObjectWithData(data!, options: nil, error: nil) as NSDictionary

                if let results = jsonDictionary["results"] as? NSDictionary{
                    if let queryResults = results[query] as? NSDictionary{
                        if let exchangeRate = queryResults["val"] as? Double{
                            let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
                            dispatch_async(dispatch_get_global_queue(priority, 0)) {
                                dispatch_async(dispatch_get_main_queue()) {
                                    completion(result: exchangeRate)
                                }
                            }

                        }
                    }
                }
            }
            else {
                completion(result: nil)
            }

        }.resume()
    }
}

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)"

            }

        }
    }

---

有没有办法让它非异步？我需要等待，直到有一个响应解析，但我不知道如何做。你的解决方案是对的，我想我的问题是错的，你可以，但这是严重不赞成的。这是一个可怕的用户体验，如果你在错误的时间做，看门狗程序可能会立即杀死你的应用程序。正确的解决方案是禁用UI，显示微调器（在iOS中，是一个

UIActivityIndicatorView

），并在请求完成时反转该过程。你真的应该接受异步模式，而不是反对它。顺便说一句，人们通常会将这些完成处理程序分派到主队列（因为调用方通常正在进行UI更新）。如果你想让我更新答案，告诉你怎么做，让我知道。如果你精通GCD，这可能是不言自明的，但如果你不精通，我很乐意向你展示。如果我这样做，它会将timeLabel设置为-999，而不是我想要的；googleDuration（startabel.text，destination:endLabel.text）{totalTime，如果让totalTime=totalTime{//在这里使用totalTime tripTime=totalTime；println（tripTime）；}}}println（“返回：”）；println（tripTime）；timeLabel.text=字符串（tripTime）是的，所以它是

self.timerLabel.text=…

。你把这个调度到主队列吗？BTW，而不是仅仅用“代码> +<代码>替换空间，你可以考虑做适当的百分比逃逸，如这里所概述的。