MVC4 Quick Tip #2–Use Delegates to setup the Dependency Resolver instead of creating a Dependency Resolver class

I’m a big fan of cutting out unneeded or unnecessary code, so here is a tip that isn’t new in MVC4, but I just discovered it and thought it was really cool and worth sharing.  When using IOC in MVC, you setup a class that implements IDependencyResolver, which has methods to return services for a given type.  While these classes where simple, it always seemed like a bit of ceremony was required whenever starting up a new MVC app.

The following example shows what a DependencyResolver class looks like using my favorite IOC framework, Ninject:

public class NinjectDependencyResolver : IDependencyResolver
             private readonly IKernel _kernel;
             public NinjectDependencyResolver(IKernel kernel)
                 _kernel = kernel;
            public object GetService(Type serviceType)
                return _kernel.TryGet(serviceType);
            public IEnumerable<object> GetServices(Type serviceType)
                return _kernel.GetAll(serviceType);

Nothing terribly complicated, but a lot of fluff.

I saw in a demo in last week’s C4MVC talk, that the DependencyResolver that was setup to create the APIController classes had some overrides I never saw before, and low and behold, the standard MVC DependencyResolver also has these overrides:


So instead of providing the SetResolver method with a DependencyResolver class, you can just provide it two delegate methods that would normally be in the DependencyResolver (GetService, and GetServices):

                     x => kernel.TryGet(x),
                     x => kernel.GetAll(x));

POW!  Cut that 20+ line class down to a method that takes two parameters.  BAM!