创建窗口xaml时为nullreferenceexception

Question

I have an issue in my WPF application, which essentially has 2 windows, a login window and a dashboard window and I get null reference exceptions intermittently when I load these windows. A typical exception looks like this (dashbaord)

Application: BlitsMe.Agent.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.NullReferenceException
Stack:
at System.Collections.Generic.Dictionary`2[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].Insert(System.__Canon, System.__Canon, Boolean)
at MS.Internal.AppModel.ResourceContainer.GetResourceManagerWrapper(System.Uri,  System.String ByRef, Boolean ByRef)
at MS.Internal.AppModel.ResourceContainer.GetPartCore(System.Uri)
at System.IO.Packaging.Package.GetPart(System.Uri)
at System.Windows.Application.LoadComponent(System.Object, System.Uri)
at BlitsMe.Agent.UI.WPF.Dashboard..ctor(BlitsMe.Agent.BlitsMeClientAppContext)
at BlitsMe.Agent.BlitsMeClientAppContext.RunDashboard()
at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext,  System.Threading.ContextCallback, System.Object, Boolean)
at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
at System.Threading.ThreadHelper.ThreadStart()

Which is an obscure error. deep in the loadcomponent class.

I start my dashboard using 2 methods in my main AppContext Class as follows

    internal void SetupAndRunDashboard()
    {
        if (DashboardUiThread == null)
        {
            DashboardUiThread = new Thread(RunDashboard) { Name = "dashboardUIThread" };
            DashboardUiThread.SetApartmentState(ApartmentState.STA);
            DashboardUiThread.Start();
        }
    }

    private void RunDashboard()
    {
        UIDashBoard = new Dashboard(this);
        Dispatcher.Run();
    }

and my dashboard constructor looks like this

public partial class Dashboard : Window
{
    public Dashboard(BlitsMeClientAppContext appContext)
    {
        this.InitializeComponent();
        ......
    }
}

I would really appreciate help on this as I am well and truly stumped since it is deep in the windows API that the null ref is being thrown.

Answer 1

OK, so I found out what is happening, albeit on quite a high level, but it seems I can't start 2 ui's concurrently. As I stated in my question, I run the login ui and dashboard ui, and I start them in the way described above, that is start a thread with STA Apartment state, the new thread then new's the login window class and hands it over to the dispatcher. But after the new thread is started the main thread goes ahead and starts its work on the dashboard window in the same fashion and as it turns out, some part of that process cannot run concurrently with another thread. Not sure why, but thats how I resolved it.

So basically the code for starting the ui's now look like this

private AutoResetEvent _dashboardStartWaitEvent = new AutoResetEvent(false);   

internal void SetupAndRunDashboard()
{
    if (DashboardUiThread == null)
    {
        DashboardUiThread = new Thread(RunDashboard) { Name = "dashboardUIThread" };
        DashboardUiThread.SetApartmentState(ApartmentState.STA);
        DashboardUiThread.Start();
        _dashboardStartWaitEvent.Wait();
    }
}

private void RunDashboard()
{
    UIDashBoard = new Dashboard(this);
    _dashboardStartWaitEvent.Set();
    Dispatcher.Run();
}

So the main thread waits for the ui to be initialised before it carries on, hence the ui's are initialised one at a time without overlapping and this resolved the issue.