Question

Background: I’m creating a WPF app using MVVM, and using a DI container to build my ViewModels

My App.xaml looks like this:

<Application x:Class='WpfApp.App'     ...xmlns etc...     StartupUri='MainWindow.xaml'>     <Application.Resources>         <app:ServiceLocator x:Key='serviceLocator' />     </Application.Resources> </Application> 

MainWindow.xaml looks like this:

<Window x:Class='CompositeMefWpfApp.MainWindow'     ...xmlns etc... >     <Control.DataContext>         <Binding Path='MainWindowViewModel' Source='{StaticResource serviceLocator}' />     </Control.DataContext> 

Now, this all works fine, but the StartupUri is hardcoded into the XAML, which I don’t want.
Following guidance of several blogposts and articles I found, I removed the StartupUri, and tried to create the MainWindow by hooking OnStartup in App.xaml.cs, like this:

protected override void OnStartup( StartupEventArgs e ) {     base.OnStartup(e);     new MainWindow().Show(); } 

The problem is, the app crashes when trying to show the window, with this exception:

Cannot find resource named ‘{serviceLocator}’. Resource names are case sensitive. Error at object ‘System.Windows.Data.Binding’ in markup file ‘WpfApp;component/mainwindow.xaml’ Line 8 Position 45.

As far as I can tell, the <Application.Resources> section is simply not being read out of the xaml file. I can put some code in the OnStartup to add the resource programatically like this:

Resources.BeginInit(); Resources.Add('serviceLocator', new ServiceLocator()); Resources.EndInit(); 

However that’s an ugly hack, and doesn’t help me if I wanted to put something else in the app.xaml file later on 🙁

Should I be hooking some other event? Is there a way around this?

Answer 1

Rather than overriding OnStartup, try using an event instead:

<Application x:Class='My.App'     xmlns='...'     Startup='Application_Startup'     ShutdownMode='OnExplicitShutdown'>         <Application.Resources>             <app:ServiceLocator x:Key='serviceLocator' />         </Application.Resources>     </Application> 

Code behind:

public partial class App : Application {     public App()     { }     private void Application_Startup(object sender, StartupEventArgs e)     {         // TODO: Parse commandline arguments and other startup work          new MainWindow().Show();     } }