How do I intercept Castle Windsor's component resolution to override dependencies?

Question

I'm looking for a way to hook into Castle Windsor's resolution process so that I can do something like:

if (componentCanBeResolvedElsewhere)
{
    return elsewhere.Resolve<TService>();
}
else
{
    windsorContainer.Resolve<TService>();
}

I want Castle Windsor to handle the majority of my dependencies, but I want to provide an ability to 'fill-in the blanks'.

I'm sure this can be done, but I'm struggling to find examples.

Answer 1

You can use dependency resolvers which let you declare that you have a special way of solving components. Here is a sample I use to resolve strings from application settings

public class AppSettingsResolver : ISubDependencyResolver
{
    public bool CanResolve(
                CreationContext context,
                ISubDependencyResolver contextHandlerResolver,
                ComponentModel model,
                DependencyModel dependency)
    {
        return !string.IsNullOrEmpty(ConfigurationManager.AppSettings[dependency.DependencyKey])
               &&
               TypeDescriptor.GetConverter(dependency.TargetType)
                .CanConvertFrom(typeof(string));
    }

    public object Resolve(
                    CreationContext context,
                    ISubDependencyResolver contextHandlerResolver,
                    ComponentModel model,
                    DependencyModel dependency)
    {
        return TypeDescriptor
            .GetConverter(dependency.TargetType)
            .ConvertFrom(ConfigurationManager.AppSettings[dependency.DependencyKey]);
    }
}

You then register the resolver in your castle container:

container.Kernel.Resolver.AddSubResolver(new AppSettingsResolver())