Question

I have a ScheduledTaskAgent project the oninvoke() method in ScheduledAgent.cs calls the fetchcurrentdetails() method in a custom defined Class Library project.

In this public string fetchcurrentdetails() method It has the following series of events.

            //class variables
            string strAddress = string.empty;
             public string fetchcurrentdetails()
              {
                GeoCoordinateWatcher watcher = new GeoCoordinateWatcher(GeoPositionAccuracy.High);
                if (watcher.Permission == GeoPositionPermission.Granted)
                 {
                  watcher.PositionChanged += new EventHandler<GeoPositionChangedEventArgs<GeoCoordinate>>(watcher_PositionChanged);    
                 }
                 return strAddress ;
              }

           private void watcher_PositionChanged(object sender, GeoPositionChangedEventArgs<GeoCoordinate> e)
             {
            WebClient bWC = new WebClient();                
            System.Uri buri = new Uri("http://dev.virtual//...");
            bWC.DownloadStringAsync(new Uri(buri.ToString()));
            bWC.DownloadStringCompleted += new                    DownloadStringCompletedEventHandler(bHttpsCompleted);
           }


          private void bHttpsCompleted(object sender, DownloadStringCompletedEventArgs bResponse)
              {
             //do some data extraction and return the string
             strAddress = "This is extracted data";
             }

the return statement always returns empty string to calling statement.Any idea how to make sure the execution retains in the class library until the method/event bHttpsCompleted() is completed ? Or what is the way to return the value when the event/method bHttpsCompleted() is fired.

Answer 1

You can modify like this

public Task<string> fetchcurrentdetails()
    {

        var tcs = new TaskCompletionSource<string>();

        GeoCoordinateWatcher watcher = new GeoCoordinateWatcher(GeoPositionAccuracy.High);
        if (watcher.Permission == GeoPositionPermission.Granted)
        {
            watcher.PositionChanged += (s, e) =>
                {
                    WebClient bWC = new WebClient();
                    System.Uri buri = new Uri("http://dev.virtual//...");
                    bWC.DownloadStringAsync(new Uri(buri.ToString()));
                    bWC.DownloadStringCompleted += (s1, e1) =>
                    {

                        if (e1.Error != null) tcs.TrySetException(e1.Error);
                        else if (e1.Cancelled) tcs.TrySetCanceled();
                        else
                            tcs.TrySetResult(e1.Result);
                        //do some data extraction and return the string                          
                    };
                };
        }
        return tcs.Task;
    }

Call : await fetchcurrentdetails()