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Task Async Await Silverlight 5 Cross-Thread Violation

Hi,
I'm trying to use the TPL in my SL5 application to simplify the Async Service calls.

I'm calling the following from my MainPage code behind, with the method being called being an async void that does the work with the service proxy. An Cross-Thread access exception always gets thrown for this code, and none of the asyn void code is reached, even though I'm not trying to interact with the UI:

var result = Task.Factory.StartNew(WCFServiceQueryHelper.StoreData);
                        await result;

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Am I missing something, or is there a better way to perform this. Basically I need to use this static method (WCFServiceQueryHelper.StoreData), wait for it to complete, without blocking the UI thread, then continue to the next method after handling any exception caught.

This is to replace all the direct service calls, and callback events in the mainpage code, as it gets very messy. The static method (WCFServiceHelper) will use async/await and interact with the ServiceProxy, meaning the MainPage code can simply call this static method, and when complete, move onto the next method.

Thanks
0
wint100
Asked:
wint100
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1 Solution
 
apeterCommented:
Can we see the complete method, "WCFServiceQueryHelper.StoreData". Looks like this method is blocking or doing something...

Just to test,  if you just have "return statement" in above method, does your code works fine ?
0
 
wint100Author Commented:
Hi,

Thanks for your feedback. Methods called are below. changing the method to return gives the same exception:

{System.UnauthorizedAccessException: Invalid cross-thread access.
   at MS.Internal.XcpImports.CheckThread()
   at System.Windows.Application.get_Host()
   at EnergyViewerV2.Helpers.ElecWCFServiceQueryHelper..cctor()}

public static async void StoreElecAnnualData()
        {
            //Annual Electric Data Collection

            if (!NetworkInterface.GetIsNetworkAvailable())
            {
                if (app.ElecAnnualData == null)
                {
                    if (DeserializeAnnualDataFromXML("ElecAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName) != null) app.ElecAnnualData = DeserializeAnnualDataFromXML("ElecAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName);
                }
                if (app.ElecPrevAnnualData == null)
                {
                    if (DeserializeAnnualDataFromXML("ElecPrevAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName) != null) app.ElecPrevAnnualData = DeserializeAnnualDataFromXML("ElecPrevAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName);
                }
            }
            else
            {
                try
                {
                    sDate = app.isRollingAnnual?RollingDatesHelper.AnnualCurrentPeriodStart().ToLongDateString(): DateTime.Now.ToLongDateString();

                    app.ElecAnnualData = await ServiceProxy.GetAnnualData(sDate,
                                                                          app.isRollingAnnual
                                                                              ? RollingDatesHelper.
                                                                                    AnnualCurrentPeriodEnd().
                                                                                    ToLongDateString()
                                                                              : null,
                                                                          app.ObjRefs[app.CurrentBuilding].elecMeter,
                                                                          app.isRollingAnnual ? 7000 : 3000, false,
                                                                          false);

                    //Store the data to IS
                    if (app.ElecAnnualData != null) SerializeAnnualDataListToXML(app.ElecAnnualData, "ElecAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName);
                    
                    sDate2 = app.isRollingAnnual ? RollingDatesHelper.AnnualPreviousPeriodStart().ToShortDateString() : DateTime.Now.AddMonths(-12).ToShortDateString();
                    app.ElecPrevAnnualData =
                        await
                        ServiceProxy.GetAnnualData(sDate2,
                                                   app.isRollingAnnual
                                                       ? RollingDatesHelper.AnnualPreviousPeriodEnd().ToShortDateString()
                                                       : null, app.ObjRefs[app.CurrentBuilding].elecMeter,
                                                   app.isRollingAnnual ? 8000 : 4000, false, false);
                     

                    //Store the data to IS
                    if (app.ElecPrevAnnualData != null) SerializeAnnualDataListToXML(app.ElecPrevAnnualData, "ElecPrevAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName);


                }
                catch (Exception ex)
                {
                    errorHandling.Error("The following error occurred trying to gather Annual Elec Data from Database: " + ex.Message, "Annual Elec Error", app.isDebugging);
                
                    if (app.ElecAnnualData == null)
                    {
                        if (DeserializeAnnualDataFromXML("ElecAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName) != null) app.ElecAnnualData = DeserializeAnnualDataFromXML("ElecAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName);
                    }
                    if (app.ElecPrevAnnualData == null)
                    {
                        if (DeserializeAnnualDataFromXML("ElecPrevAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName) != null) app.ElecPrevAnnualData = DeserializeAnnualDataFromXML("ElecPrevAnnual" + app.ObjRefs[app.CurrentBuilding].BuildingNo + app.ObjRefs[app.CurrentBuilding].BuildingName);
                    }


                }
            }




        }

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With the ServiceProxy class as follows:

public class ServiceProxy
    {
        static Uri address = new Uri(Application.Current.Host.Source, "../Services/SilverlightService.svc");

        public static Task<ObservableCollection<EnergyData>> GetAnnualData(string sDate, string eDate, string MeterID, int index,
                                              bool occupancyRequired, bool tempRequired)
        {
            var tcs = new TaskCompletionSource<ObservableCollection<EnergyData>>();

            var client = new SilverlightServiceClient("CustomBinding_SilverlightService", address.AbsoluteUri);

            client.getAnnualDataCompleted += (s, e) =>
            {
                if (e.Error != null)
                    tcs.TrySetException(e.Error);
                else if (e.Cancelled)
                    tcs.TrySetCanceled();
                else
                    tcs.TrySetResult(e.Result);
            };

            client.getAnnualDataAsync(sDate,eDate,MeterID,index,occupancyRequired,tempRequired);

            return tcs.Task;
        }

    }

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0
 
wint100Author Commented:
Checking though my code, it looks like I'm calling the first method within a new Threadpool.QueueUserWorkItem:

ThreadPool.QueueUserWorkItem(delegate
                                                   {

CallMethod();
};
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apeterCommented:
From the code, it doesn't looks like accessing any UI element.   Did you tried to call debug and fine which line the error is thrown? Maybe a test method which call just the above method.
0
 
wint100Author Commented:
I removed the Threadpool code and the problem went away. It must have been firing in a different thread due to the threadpool.

Thanks
0
 
wint100Author Commented:
Found the solution
0
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