Question

I have read up about this problem I am having and I cannot seem to find a solution for it. Some people have recommended to use the dispatcher to push the code execution onto the UI Thread. However this does not solve my issue. I am calling this code out of an Asyc method which is before hand called by a Guide object to display a notification. The code which controls the UI stuff is as follows:

public bool isDisabled
{
    set
    {
        if (value)
        {
            Deployment.Current.Dispatcher.BeginInvoke(() =>
                {
                    color = new SolidColorBrush(Colors.Gray);
                });
            enabled = false;
        }
        else
        {
            Deployment.Current.Dispatcher.BeginInvoke(() =>
                {
                    color = origionalColor;
                });
            enabled = true;
        }
    }
}

and it is being called from

    private void nameInputFinished(IAsyncResult ar)
    {
        int? result = Guide.EndShowMessageBox(ar);

        if (result == 0)
        {
             [...]

             JourneyPanels.getPanel(JourneyPanelTypes.integration).isDisabled = false;
        }
    }

Not sure why I am getting the corss-thread exception but I am pretty sure it has something to do with the async method nesting.

Any help is greatly appreciated!

EDIT: Full Exception Stack

  {System.UnauthorizedAccessException: Invalid cross-thread access.
  at MS.Internal.XcpImports.CheckThread()
  at MS.Internal.XcpImports.SetValue(IManagedPeerBase obj, DependencyProperty property, Boolean b)
  at System.Windows.DependencyObject.SetValue(DependencyProperty property, Boolean b)
  at System.Windows.Controls.TextBox.set_IsReadOnly(Boolean value)
  at PocketRitual.Journey.nameInputFinished(IAsyncResult ar)
  at Microsoft.Xna.Framework.GamerServices.ActionDialogHelper.Complete()
  at Microsoft.Xna.Framework.GamerServices.ActionDialogHelper.GetMessageBoxResult(Object state)
  at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
  at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
  at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
  at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
  at System.Threading.ThreadPoolWorkQueue.Dispatch()
  at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()}

Answer 1

It’s your calling code you need to run on the main UI thread e.g.

Deployment.Current.Dispatcher.BeginInvoke(() => {
    JourneyPanels.getPanel(JourneyPanelTypes.integration).isDisabled = false;
});

There is no need to call Dispatcher on your internal property changes because you will be running on the UI thread at that point.