Cross-thread Exception while creating WPF window - wpf

Question

In my application (.NET 4.0) I use smartassembly for error reporting with a custom template. It installs two handlers:
It installs a global exception catcher, and calls my custom code if an exception occurs. There I display a WPF window which shows the details of the exception and allows the user to send the data via the internet.
If an exception occurs which cannot be handled by #1, it calls a fatal exception handler. There I output the exception data in a message box.
On one customer's machine (Windows XP, .NET 4.0) he gets an error message from #2 after the application starts. Then the application is terminated:
System.InvalidOperationException: The calling thread cannot access this object because a different thread owns it.
at System.Windows.Threading.Dispatcher.VerifyAccess()
at Exapt.ErrorReporting.ErrorReportView..ctor()
at Exapt.ErrorReporting.ExaptUnhandledExceptionHandler.OnReportException(ReportExceptionEventArgs e)
at SmartAssembly.SmartExceptionsCore.UnhandledExceptionHandler.ReportException(Exception exception, Boolean canContinue, Boolean manuallyReported)
The relevant code:
public ExaptUnhandledExceptionHandler : UnhandledExceptionHandler
{
protected override void OnReportException(ReportExceptionEventArgs e)
{
var view = new ErrorReportView();
view.DataContext = new ErrorReportViewModel(this, e, view);
view.ShowDialog();
}
}
public ErrorReportView : Window
{
public ErrorReportView()
{
this.InitializeComponent();
// EDIT
if (Application.Current != null)
this.Owner = Application.Current.MainWindow;
// END EDIT
}
}
So the following happens:
During startup an exception occurs (unfortunately, this gets lost).
To handle the exception, smartassembly calls the handler #1, OnReportException().
There I create a new ErrorReportView.
WPF throws a cross-thread exception in the constructor (before InitializeComponent())!
Because an exception occurred while handling the exception, smartassembly calls the handler #2 and terminates the application.
How is it possible that a simple new Window() can cause a cross-thread exception on itself?

Answer 1

Try to create your ErrorReportView using the WPF Dispatcher :
public ExaptUnhandledExceptionHandler : UnhandledExceptionHandler
{
protected override void OnReportException(ReportExceptionEventArgs e)
{
Application.Current.Dispatcher.Invoke(new Action(() =>
{
var view = new ErrorReportView();
view.DataContext = new ErrorReportViewModel(this, e, view);
view.ShowDialog();
}));
}
}
As I can't test it or reproduce your issue, I'm not sure it will work, but it's worth a try.

Answer 2

An option is to fire a dedicated thread to handle this report. It would be something like this:
[TestMethod]
public void TestMethod1()
{
MainWindow window = null;
// The dispatcher thread
var t = new Thread(() =>
{
window = new MainWindow();
// Initiates the dispatcher thread shutdown when the window closes
window.Closed += (s, e) => window.Dispatcher.InvokeShutdown();
window.Show();
// Makes the thread support message pumping
System.Windows.Threading.Dispatcher.Run();
});
// Configure the thread
t.SetApartmentState(ApartmentState.STA);
t.Start();
t.Join();
}
Note that:
The window must be created and shown inside the new thread.
You must initiate a dispatcher (System.Windows.Threading.Dispatcher.Run()) before the ThreadStart returns, otherwise the window will show and die soon after.
The thread must be configured to run in STA apartment.
You can find additional information in this link.

Answer 3

With Arthur Nunes's answer and Sisyphe's answer I now handle all possibilities. The exception is apparently being thrown on an STA thread, but that thread is not the main (UI) thread. Probably due to JIT optimizations, the stack trace I got is a little incomplete and shows the exception happening at the wrong place.
The fixed code:
public ExaptUnhandledExceptionHandler : UnhandledExceptionHandler
{
protected override void OnReportException(ReportExceptionEventArgs e)
{
// Create a new STA thread if the current thread is not STA.
if (Thread.CurrentThread.GetApartmentState() == ApartmentState.STA)
{
this.ShowErrorReportView(e);
}
else
{
// Since I use ShowDialog() below, there is no need for Dispatcher.Run()
// or Dispatcher.InvokeShutdown()
var thread = new Thread(() => this.ShowErrorReportView(e));
thread.SetApartmentState(ApartmentState.STA);
thread.Start();
thread.Join();
}
}
private void ShowErrorReportView(ReportExceptionEventArgs e)
{
var view = new ErrorReportView();
view.DataContext = new ErrorReportViewModel(this, e, view);
view.ShowDialog();
}
}
public ErrorReportView : Window
{
public ErrorReportView()
{
this.InitializeComponent();
// All of these cause accessing the MainWindow property or setting the Owner
// to throw an exception.
if (Application.Current != null
&& Application.Current.Dispatcher.CheckAccess()
&& Application.Current.MainWindow != null
&& Application.Current.MainWindow != this
&& Application.Current.MainWindow.IsLoaded)
{
this.Owner = Application.Current.MainWindow;
}
}
}