Optional Dependency at Composition Root

Question

I've written a WPF app that has two different main windows. I don't know which one to launch until runtime by looking up what kind of user is using the program in a database. The code I currently have works but Castle Windsor is doing tons of extra work by newing up the object graphs for both kinds of windows.

    private readonly IMainWindow _mainWindow;
    private readonly ISimplifiedMainWindow _simplifiedMainWindow;

    public MainClass(
        IMainWindow mainWindow,
        ISimplifiedMainWindow simplifiedMainWindow)
    {            
        _mainWindow = mainWindow;
        _simplifiedMainWindow = simplifiedMainWindow;
    }

    public RunApp()
    { // pseudocode
        if (user is fullUser) _mainWindow.Show();
        else _simplifiedMainWindow.Show();
    }

How do I defer creation of my window objects without resorting to making an abstract factory that will basically duplicate what Castle Windsor does anyway?

Answer 1

A factory is in fact the solution I'd recommend (and a solution I've successfully used multiple times in the past to solve this very problem).

I wouldn't implement the factory myself though, let Windsor do it (via a Typed Factory).

public interface IWindowFactory
{
   IMainWindow FullUserWindow();
   ISimplifiedMainWindow SimplifiedUserWindow();

   //optionally
   void DestroyWindow(IWindow window);
}

Now you just need to tell Windsor to build a factory for that interface

container.AddFacility<TypedFactoryFacility>();
// later on, in your installer
container.Register(Component.For<IWindowFactory>()
                      .AsFactory()
                      .LifestyleTransient());

and your app code changes to:

public RunApp()
{ // pseudocode
    if (user is fullUser) Show(factory.FullUserWindow());
    else Show(factory.SimplifiedUserWindow());
}