Carlos Rodriguez Carlos Rodriguez - 23 days ago 8
C# Question

Unity IoC does not inject dependency into Web API Controller

I'm very new to using Unity, but my problem is that whenever I call my web service, I get an exception stating that

"Make sure that the controller has a parameterless public constructor"

I've followed multiple tutorials and I still get the same issue.

In the Register function of my WebApiConfig class, I have

var container = new UnityContainer();
container.RegisterType<IValidator, Validator>(new HierarchicalLifetimeManager());
config.DependencyResolver = new UnityResolver(container);


Here is my UnityResolver class

using Microsoft.Practices.Unity;
using System;
using System.Collections.Generic;
using System.Web.Http.Dependencies;

public class UnityResolver : IDependencyResolver
{
protected IUnityContainer container;

public UnityResolver(IUnityContainer container)
{
if (container == null)
{
throw new ArgumentNullException("container");
}
this.container = container;
}

public object GetService(Type serviceType)
{
try
{
return container.Resolve(serviceType);
}
catch (ResolutionFailedException)
{
return null;
}
}

public IEnumerable<object> GetServices(Type serviceType)
{
try
{
return container.ResolveAll(serviceType);
}
catch (ResolutionFailedException)
{
return new List<object>();
}
}

public IDependencyScope BeginScope()
{
var child = container.CreateChildContainer();
return new UnityResolver(child);
}

public void Dispose()
{
container.Dispose();
}
}


I have not registered any controllers, as every tutorial claims that I don't need to do this. Here is my actual controller

public class Controller: ApiController
{
private IValidator _validator;

public Controller(IValidator validator)
{
this._validator = validator;
}

[HttpPost]
public void ReceiveIPN()
{

}
}


Does anyone have any ideas as to what I can be doing wrong? Thanks!

EDIT 1: Here is the "implementation" of the Validator class. It's pretty empty, because I didn't want to introduce a bug here until I resolved the Unity issue.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;


public class Validator: IValidator
{
public bool ValidateIPN(string body)
{
throw new NotImplementedException();
}
}


EDIT 2: Here is the entire error response I get when I attempt to call the web api route using Fiddler


{"message":"An error has occurred.","exceptionMessage":"An error
occurred when trying to create a controller of type 'Controller'. Make
sure that the controller has a parameterless public
constructor.","exceptionType":"System.InvalidOperationException","stackTrace":"
at
System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage
request, HttpControllerDescriptor controllerDescriptor, Type
controllerType) at
System.Web.Http.Controllers.HttpControllerDescriptor.CreateController(HttpRequestMessage
request) at
System.Web.Http.Dispatcher.HttpControllerDispatcher.d__1.MoveNext()","innerException":{"message":"An
error has occurred.","exceptionMessage":"Type 'Project.Controller'
does not have a default
constructor","exceptionType":"System.ArgumentException","stackTrace":"
at System.Linq.Expressions.Expression.New(Type type) at
System.Web.Http.Internal.TypeActivator.Create[TBase](Type
instanceType) at
System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage
request, Type controllerType, Func`1& activator) at
System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage
request, HttpControllerDescriptor controllerDescriptor, Type
controllerType)"}}

Answer

So, after hours of banging my head against a wall, I've found that this wasn't working because I had an OWIN/Katana Startup.cs class in my project. Now I don't know exactly what's going on here, so any more information would be great.

Basically, since I was using OWIN/Katana, I had a Startup.cs file that created a new HttpConfiguration object and configured it, similar to how it's done in the WebApiConfig.cs class.

private void ConfigureWebApi(HttpConfiguration config)
{
    config.MapHttpAttributeRoutes();
    var container = new UnityContainer();
    container.RegisterType<IValidator, Validator>();
    config.DependencyResolver = new UnityDependencyResolver(container);

    var jsonFormatter = config.Formatters.OfType<JsonMediaTypeFormatter().First();
    jsonFormatter.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
}

It looks like the code first runs through the WebApiConfig's Register function, and THEN overrides that HttpConfiguration object with the one generated in the Startup.cs file. I had to move my container setup stuff here in order for it to work.

Sorry that I didn't bring up the OWIN stuff before. This is fairly new to me and I didn't realize it was relevant. Hopefully this saves someone else the pain that I've just been through.