Set Inner Dependency by Type using Structuremap

Question

I have a structuremap configuration that has me scratching my head. I have a concrete class that requires a interfaced ui element which requires an interfaced validation class. I want the outer concrete class to get the default ui element, but get a concrete-class-specific validation object. Something like this:

class MyView 
{
   IPrompt prompt
}

class GenericPrompt : IPrompt
{
   IValidator validator
}

class MyValidator : IValidator
{
   bool Validate() {}
}

How can I configure structuremap with the Registry DSL to only use MyValidator when creating dependencies for MyView. (And assumedly using BobsValidator when creating dependencies for BobsView)

Answer 1

Are you getting MyView (and BobsView) from the container? Can we assume that they will all take an instance of IPrompt?

One approach would be to register all of your validators with a name that matches the names of your view. You could implement your own type scanner that just removes the Validator suffix:

public class ValidatorScanner : ITypeScanner
{
    public void Process(Type type, PluginGraph graph)
    {
        if (!typeof (IValidator).IsAssignableFrom(type)) return;
        var validatorName = type.Name.Replace("Validator", "");
        graph.AddType(typeof(IValidator), type, validatorName);
    }
}

Now, if you assume an IPrompt will always be requested by a View that follows that naming convention, your registry could look like:

public class ValidatorRegistry : Registry
{
    public ValidatorRegistry()
    {
        Scan(scan =>
        {
            scan.TheCallingAssembly();
            scan.With<ValidatorScanner>();
        });

        ForRequestedType<IPrompt>().TheDefault.Is.ConstructedBy(ctx =>
        {
            var viewName = ctx.Root.RequestedType.Name.Replace("View", "");
            ctx.RegisterDefault(typeof(IValidator), ctx.GetInstance<IValidator>(viewName));
            return ctx.GetInstance<GenericPrompt>();
        });
    }
}

To retrieve your view with the appropriate validator, you would have to request the concrete type:

var view = container.GetInstance<MyView>();

Note that this will only work if you are retrieving your view with a direct call to the container (service location), since it depends on the "Root.RequestedType". Depending on how you plan to get your views, you might be able to walk up the BuildStack looking for a View (instead of assuming it is always Root).