WPF application continues even after explicit shutdown - wpf

Question

I have a simple wpf application that continues to run even after I explicitly call it to shut down.
It integrates with a third party application and needs to check that a few documents of a certain type and with specific content are open as it initializes.
Here is a portion of the initialization code:
try
{
ActiveProductDoc = Automation.CATIA.ActiveDocument as ProductDocument;
}
catch
{
InvalidAssemblyShutdown("You must have an assembly open before you run the app");
}
if(ActiveProduct == null)
InvalidAssemblyShutdown("You must have one assembly open (not a part)");
ActiveProduct = ActiveProductDoc.Product;
And here is the InvalidAssemblyShutdown method:
private void InvalidAssemblyShutdown(string message)
{
MessageBox.Show(message);
Close();
Application.Current.Shutdown();
}
I have set the application's ShutdownMode property to OnMainWindowClose.
I am currently doing a use case test where the user has the wrong type of document open and so the ActiveProduct field is null. The InvalidAssemblyShutdown method is called as expected but despite this the line in the initialization method following the shutdown call still runs and throws an exception.
Any ideas what's going on?
Should I throw exceptions instead and use a global exception handler?

Answer 1

If you have a look at the source code for Application.Current.Shutdown (link to source), you'll see that it uses Dispatcher.BeginInvoke() to initiate the shutdown. In other words, the shutdown gets queued on the UI thread. It doesn't take effect during that precise method call, so the following code keeps executing.
You'll need to exit the code right after the call to Application.Current.Shutdown if you don't want some code to run while the shutdown request gets processed. Something like:
if(ActiveProduct == null)
{
InvalidAssemblyShutdown("You must have one assembly open (not a part)");
return; // prevent further code execution.
}
For what it's worth, this.Close() works in a similar way. So if you have proper flow control, you won't need to invoke Application.Current.Shutdown at all. Your call to this.Close() should be enough.