在其他与web服务一起工作的swift文件中调用func不会返回任何结果

Question

在swift 2中，当我与web服务通信时，当我用按钮操作编写这些代码时，它工作得很好。

let alert = UIAlertController(title: "Alert", message: "Message", preferredStyle: .Alert)
    let ok = UIAlertAction(title: "OK", style: .Default, handler: { (action) -> Void in })
    alert.addAction(ok);
    let request = NSMutableURLRequest(URL: NSURL(string: "http://www.myaddress.com/web-service/iostest.aspx")!)
    request.HTTPMethod = "POST"
    var postString = String();
    postString = "uid=1";
    request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
    let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
        guard error == nil && data != nil else {
            alert.title="Error"
            alert.message = "Connection error"
            dispatch_async(dispatch_get_main_queue()){
                self.presentViewController(alert, animated: true, completion: nil)
            }
            return
        }
        if let httpStatus = response as? NSHTTPURLResponse where httpStatus.statusCode != 200 {
            alert.title="Error"
            alert.message = "Server error"
            dispatch_async(dispatch_get_main_queue()){
                self.presentViewController(alert, animated: true, completion: nil)
            }
        }
        let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
        alert.title="Info"
        alert.message = responseString as? String
        dispatch_async(dispatch_get_main_queue()){
            self.presentViewController(alert, animated: true, completion: nil)
        }
    }
    task.resume()

正如我所说，这很好，但由于我也想从不同的ViewControls中完成这项工作，我创建了一个swift文件，该文件包含一个结构和一个静态函数，该函数在该结构中返回"responseString"，这样我就可以在视图控件中提醒它。类似这样的东西：

struct globalClass {
static func sendInfo(url: String, data: String) -> (answer: String, errorCode: Int32) {
    var res = String();
    var err = Int32();
    err = 0;
    let request = NSMutableURLRequest(URL: NSURL(string: url)!);
    request.HTTPMethod = "POST";
    let postString: String = data;
    request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding);
    let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
        guard error == nil && data != nil else {
            err = 1;
            return;
        }
        if let httpStatus = response as? NSHTTPURLResponse where httpStatus.statusCode != 200 {
            err = 2;
            return;
        }
        let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding);
        res = (responseString as? String)!;
    }
    task.resume();
    return (res, err);
}

但现在，当我从按钮调用这个函数时，它会很快向我显示一个空警报，表明它似乎没有从web服务中得到任何东西，甚至没有尝试。

我把这些放在按钮动作中：

@IBAction func btnData(sender: AnyObject) {
    let y: String = "uid=1";
    let res = globalClass.sendInfo("http://www.myaddress.com/web-service/iostest.aspx", data: y);
    let alert = UIAlertController(title: "", message: "", preferredStyle: .Alert);
    let OK = UIAlertAction(title: "OK", style: .Default, handler: nil);
    alert.addAction(OK);
    if (res.errorCode==0) {
        alert.title = "Info";
        alert.message = res.answer;
    } else if (res.errorCode==1) {
        alert.title = "Error";
        alert.message = "Error connecting to server";
    } else {
        alert.title = "Error";
        alert.message = "Server returned an error";
    }
    dispatch_async(dispatch_get_main_queue()){
        self.presentViewController(alert, animated: true, completion: nil);
    };
}

感谢您的帮助，

Afshin Mobayen Khiabani

Answer 1

globalClass.sendInfo使用异步调用-dataTaskWithRequest。请求的结果将在完成此方法时交付。但您并没有等待结果，而是尝试像使用同步函数一样使用sendInfo。

为了能够从dataTaskWithRequest的完成中传递结果，将您自己的完成放入sendInfo中，并在传递结果时调用此完成(闭包(。示例

struct GlobalClass {
    static func sendInfo(url: String, data: String, completion: (answer: String?, errorCode: Int32?) -> Void) {
        // you code here which prepares request
        let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
            // you parse the result here
            // you deliver the result using closure
            completion(string, error)
        }
        task.resume();
    }
}

还有一个用法示例：

func usage() {
    GlobalClass.sendInfo("url", data: "data") { (answer, errorCode) in
        // your answer and errorCode here
        // handle the result
    }
}

Answer 2

static func sendInfo(url: String, data: String, completion: (answer: String, errorCode: Int32) -> ()){
//Your code..
        let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding);
        res = (responseString as? String)!;
     completion(answer: res, errorCode: err)
    }
    task.resume()

}

然后当你呼叫sendInfo时，这样呼叫：

sendInfo(url: "your url", data: "your data") { (result, error) in
//you use your result and error values as u want.
}