Silverlight: WebContext is not available exception crashes visual studio
I have a prism app using RIA services, and my authentication service is in a separate RIA class library.
The program works fine at runtime. Authentication and all.
I am getting a nasty error at design time, though, which crashes both visual studio and blend. Blend will crash immediately when I open the solution. Visual studio will crash when I close the particular view (page). At least blend gave me a crash log after though. The error has to do with me setting an instance of my viewmodel as the datacontext of the view in xaml rather than setting/injecting one at runtime.
So when setting a viewmodel datacontext at runtime, the viewmodel constructor is called when the view is loaded in the designer. And when the view is closed the destructor is called. That is where I am getting the exception that crashes vs/blend. So here is the exception:
System.InvalidOperationException: The current instance of WebCo开发者_如何学Cntext is not available. You must instantiate a WebContext and add it to Application.ApplicationLifetimeObjects within the default App constructor. at System.ServiceModel.DomainServices.Client.ApplicationServices.WebContextBase.get_Current() at MyClassLibrary.WebContext.get_Current() at MyShellProject.ShellViewModel.Finalize()
It's odd because I am instantiating a WebContext in my App constructor. And there are no problems at runtime. Only since I added an instance of my viewmodel as the datacontext I get the crash at runtime.
So in my App.xaml I have:
<Application.ApplicationLifetimeObjects>
<MyClassLibrary:WebContext>
<MyClassLibrary:WebContext.Authentication>
<ApplicationServices:FormsAuthentication>
<ApplicationServices:FormsAuthentication.DomainContext>
<MyClassLibrary_Web:MyAuthenticationContext />
</ApplicationServices:FormsAuthentication.DomainContext>
</ApplicationServices:FormsAuthentication>
</MyClassLibrary:WebContext.Authentication>
</MyClassLibrary:WebContext>
</Application.ApplicationLifetimeObjects>
I did also try the code behind equivalent of this in the App constructor. Both have the same result.
This blog post has a little more detail about how my project is set up: http://avcode.wordpress.com/2010/08/25/authenticaion-prism-wcf-ria-services/
Anyone have a clue as to why at design time, visual studio is not aware that I have instantiated a WebContext?
Let's say you have the following variable in ViewModel:
public bool IsDesignTime
{
get
{
return DesignerProperties.GetIsInDesignMode(Application.Current.RootVisual);
}
}
You can wrap the piece of code which tries to instantiate the WebContext at design time using this variable's value and return a Mocked object instead. I think WebContext is instantiated when the App is running and connected, not sure though. Late reply but may be useful to someone.
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