斯威夫特：如何在异步urlsession函数中返回值？

斯威夫特：如何在异步urlsession函数中返回值？

您应该添加自己的

completionHandler

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

NSURLSessionTask

如果调用者希望能够取消任务，我也将获得此返回。

无论如何，您可以这样称呼它：

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