Window Loaded and WPF

I have a WPF project in Windows 2012 in which I need to load some information in the Window Loaded event. I need to do this in the View Model rather than in the CodeBehind, though. I am attempting to use the following code:

In my xaml:

<interactivity:Interaction.Behaviors>
    <behaviors:WindowLoadedBehavior LoadedCommand="{Binding WindowLoadedCommand}" />
</interactivity:Interaction.Behaviors>

In my View Model:

private DelegateCommand _WindowLoadedCommand;

public DelegateCommand WindowLoadedCommand
{
    get
    {
        return _WindowLoadedCommand;
    }
    private set
    {
        _WindowLoadedCommand = value;
    }
}

public ShellViewModel()
{
    WindowLoadedCommand = new DelegateCommand(WindowLoadedAction);
}

protected void WindowLoadedAction()
{
    ...
}

My attached behavior:

public class WindowLoadedBehavior : Behavior<FrameworkElement>
{
    [SuppressMessage("Microsoft.StyleCop.CSharp.MaintainabilityRules", "SA1401:FieldsMustBePrivate", Justification = "Dependency Property.  Allow public.")]
    public static DependencyProperty LoadedCommandProperty = DependencyProperty.Register("LoadedCommand", typeof(ICommand), typeof(WindowLoadedBehavior), new PropertyMetadata(null));

    public ICommand LoadedCommand
    {
        get { return (ICommand)GetValue(LoadedCommandProperty); }
        set { SetValue(LoadedCommandProperty, value); }
    }

    protected override void OnAttached()
    {
        base.OnAttached();

        AssociatedObject.Loaded += AssociatedObject_Loaded;
    }

    protected override void OnDetaching()
    {
        AssociatedObject.Loaded -= AssociatedObject_Loaded;

        base.OnDetaching();
    }

    private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
    {
        if (LoadedCommand != null)
            LoadedCommand.Execute(null);
    }
}

The OnAttached, AssociatedObject_Loaded and LoadedCommand get are all firing, but the LoadedCommand set is not firing and, obviously, the WindowLoadedCommand isn't firing. Any clue what I can do to get this working?

There are a few options. A couple of them listed here:

how to call a window's Loaded event in WPF MVVM?

However, in the off chance that you or anyone else cares that you are spending several hours to complete a task that should have taken 30 seconds, you might want to try this instead.

public MainWindow()
{
    InitializeComponent();

    this.Loaded += new RoutedEventHandler(MainWindow_Loaded);
}

void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
    ShellViewModel.Instance.WindowLoadedCommand.Execute(null);
}