Decorators with different constructor arguments

Question

Using Castle Windsor, I\'d like to create a class that records an integer. But I\'d like to decorate it several times with other classes. I can see how this works if all c

Answer 1

I've found a solution that I believe is the way this should be done. Down in the innards of Windsor the DefaultDependencyResolver has a method it uses to resolve sub-dependencies (such as a decorated instance of IRecorder above) called RebuildContextForParameter. It calls this to create a new context to use when resolving the dependency (i.e. the parameter to the constructor). The method is:

/// 
This method rebuild the context for the parameter type. Naive implementation.
protected virtual CreationContext RebuildContextForParameter(CreationContext current, Type parameterType)
{
    if (parameterType.ContainsGenericParameters)
    {
        return current;
    }

    return new CreationContext(parameterType, current, false);
}

The false parameter in CreationContext constructor is propagateInlineDependencies, which when true will copy over the current context's AdditionalArguments, thereby passing down the parameters to the sub-dependencies.

To flip this false to true, create a new class that derives from DefaultDependencyResolver:

public class DefaultDependencyResolverInheritContext : DefaultDependencyResolver
{
    protected override CreationContext RebuildContextForParameter(CreationContext current, Type parameterType)
    {
        if (parameterType.ContainsGenericParameters)
        {
            return current;
        }

        return new CreationContext(parameterType, current, true);
    }
}

Then use that when creating the Windsor container:

var kernel = new DefaultKernel(
                 new DefaultDependencyResolverInheritContext(), 
                 new NotSupportedProxyFactory());
var container = new WindsorContainer(kernel, new DefaultComponentInstaller());

The NotSupportedProxyFactory and DefaultComponentInstaller are the defaults when using the parameter-less constructors for DefaultKernel and WindsorContainer.

When done, the code above will work when a factory is used to create an IRecorder, i.e.:

// during type registration/bootstrapping
container.AddFacility();
container.Register(Component.For().ImplementedBy());
container.Register(Component.For().ImplementedBy());
container.Register(Component.For().AsFactory());

Where IRecorderFactory is:

public interface IRecorderFactory
{
    IRecorder Create(int seed);
}

Then this will work as expected:

IRecorderFactory recorderFactory = container.Resolve();
IRecorder recorder = recorderFactory.Create(20);
recorder.Add(6);

Hopefully that helps others!