Question

I have a simple WPF application which I am trying to start. I am following the Microsoft Patterns and Practices ‘Composite Application Guidance for WPF’. I’ve followed their instructions however my WPF application fails immediately with a ‘TypeInitializationException’.

The InnerException property reveals that ‘The type initializer for ‘System.Windows.Navigation.BaseUriHelper’ threw an exception.’

Here is my app.xaml:

<Application x:Class='MyNamespace.App'     xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'     xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>     <Application.Resources>              </Application.Resources> </Application> 

And here is my app.xaml.cs (exception thrown at ‘public App()’):

public partial class App : Application {     public App()     {         Bootstrapper bootStrapper = new Bootstrapper();         bootStrapper.Run();     } } 

I have set the ‘App’ class as the startup object in the project.

What is going astray?

Answer 1

Thanks @ima, your answer pointed me in the right direction. I was using an app.config file and it contained this:

<configuration>   <startup>     <supportedRuntime version='v2.0.50727' sku='Client'/>   </startup>   <configSections>     <section name='modules' type='Microsoft.Practices.Composite.Modularity.ModulesConfigurationSection, Microsoft.Practices.Composite'/>   </configSections>   <modules>     <module assemblyFile='Modules/MyNamespace.Modules.ModuleName.dll' moduleType='MyNamespace.Modules.ModuleName.ModuleClass' moduleName='Name'/>   </modules> </configuration> 

It seems the problem was the <startup> element because when I removed it the application ran fine. I was confused because Visual Studio 2008 added that when I checked the box to utilise the ‘Client Profile’ available in 3.5 SP1.

After some mucking about checking and un-checking the box I ended up with a configuration file like this:

<configuration>   <configSections>     <section name='modules' type='Microsoft.Practices.Composite.Modularity.ModulesConfigurationSection, Microsoft.Practices.Composite'/>   </configSections>   <modules>     <module assemblyFile='Modules/MyNamespace.Modules.ModuleName.dll' moduleType='MyNamespace.Modules.ModuleName.ModuleClass' moduleName='Name'/>   </modules>   <startup>     <supportedRuntime version='v2.0.50727' sku='Client'/>   </startup> </configuration> 

Which works!

I’m not sure why the order of elements in the app.config is important – but it seems it is.