C# WPF Updating UI from Worker Thread

Question

using System;
using System.Linq;
using Microsoft.Practices.Prism.MefExtensions.Modularity;
using Samba.Domain.Models.Customers;
using Samba.Localization.Properties;
using Samba.Persistance.Data;
using Samba.Presentation.Common;
using Samba.Presentation.Common.Services;
using System.Threading;


namespace Samba.Modules.TapiMonitor
{
    [ModuleExport(typeof(TapiMonitor))]
    public class TapiMonitor : ModuleBase
    {

        public TapiMonitor()
        {
            Thread thread = new Thread(() => OnCallerID());
            thread.SetApartmentState(ApartmentState.STA); //Set the thread to STA
            thread.Start();
        }

        public void CallerID()
        {
            InteractionService.UserIntraction.DisplayPopup("CID", "CID Test 2", "", "");
        }

        public void OnCallerID()
        {
            this.CallerID();
        }
    }
}

I'm trying to add something to a opensource software package made in C# but I'm having problems with it. The problem with the above (simplified) example is that once InteractionService.UserIntraction.DisplayPopup is called I get an exception "The calling thread cannot access this object because a different thread owns it".

I am not a C# coder but I have tried many things to solve this like Delegates, BackgroundWorkers, etc. etc. and none have worked for me so far.

Can anybody help me with this?

What is something. Where is your Interaction.DisplayPopup code? A delegate should be able to solve the issue — Chibueze Opata, Feb 22 '13 at 10:20
Related: http://stackoverflow.com/questions/11923865/how-to-deal-with-cross-thread-access-exceptions — H.B., Feb 22 '13 at 14:29

score 2 · Answer 1 · edited Feb 22 '13 at 10:21

2

Consider calling the method on the UI thread through the Dispatcher. In your case I believe you should pass in the UI dispatcher as a parameter to the constructor of the type you've described and save it in a field. Then, when calling you can do the following:

if(this.Dispatcher.CheckAccess())
{
    InteractionService.UserInteration.DisplayPopup(...);
}
else
{
    this.Dispatcher.Invoke(()=>this.CallerID());
}

edited Feb 22 '13 at 10:21

Chibueze Opata

9,856
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answered Feb 22 '13 at 10:19

Artak

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I have already tried that but the problem is that the Dispatcher isn't available in the ModuleBase class and I wasn't successful at adding one. :( – Demigod Feb 22 '13 at 10:27
There is the ConsoleHoster open-source WPF project, where the Dispatcher is being passed in to the VM. You can take a look to the ViewModelBase class in there to see how its done. But the solution is the same. The link to it is: http://consolehoster.codeplex.com – Artak Feb 22 '13 at 10:49

score 0 · Answer 2 · answered Feb 22 '13 at 11:06

You can write your own DispatcherHelper to acces the Dispatcher from ViewModels. I think it is MVVM friendly. We used an implementation in our app like this:

public class DispatcherHelper
    {
        private static Dispatcher dispatcher;

        public static void BeginInvoke(Action action)
        {
            if (dispatcher != null)
            {
                dispatcher.BeginInvoke(action);
                return;
            }
            throw new InvalidOperationException("Dispatcher must be initialized first");
        }

        //App.xaml.cs
        public static void RegisterDispatcher(Dispatcher dispatcher)
        {
            DispatcherHelper.dispatcher = dispatcher;
        }
    }

C# WPF Updating UI from Worker Thread

2 Answers2