Refactoring_to_improve_maintainability_and_blendability_using_IoC_part_2_05.cs

public abstract class ViewModelFactory
{
    protected static IViewModelResolver resolver = null;
    public static void InitializeResolver(IViewModelResolver resolver)
    {
        // This is where we set the resolver for the ViewModelFactory.
        // This should get set in the Bootstrapper (Composition Root)
        // to the resolver implementation using the
        // IoC container that has been chosen for the application.
        ViewModelFactory.resolver = resolver;
    }
}

public abstract class ViewModelFactory<TViewModel, TDesignViewModel>
    : ViewModelFactory
    where TViewModel : IViewModel
    where TDesignViewModel : TViewModel, new()
{
    public ViewModelFactory()
    {
    }

    public TViewModel ViewModel
    {
        get
        {
            TViewModel viewModel;
            bool designMode = DetectDesignMode();

            if (designMode)
            {
                viewModel = new TDesignViewModel();
            }
            else
            {
                if (resolver == null)
                {
                    throw new InvalidOperationException();
                }

                // Use the resolver implementation to resolve
                // the view model requested.
                viewModel = (TViewModel)resolver.Resolve(typeof(TViewModel));
            }

            viewModel.OnLocated();
            return viewModel;
        }
    }
}