Difficulty getting Unity dependency injection working with WebAPI, and OWIN

Question

When I try to call a controller API endpoint on my application I get this error:

   {
  "Message": "An error has occurred.",
  "ExceptionMessage": "An error occurred when trying to create a controller of type 'ProviderController'. 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)\r\n   at System.Web.Http.Controllers.HttpControllerDescriptor.CreateController(HttpRequestMessage request)\r\n   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()",
  "InnerException": {
    "Message": "An error has occurred.",
    "ExceptionMessage": "Type 'mynamespace.api.controllers.ProviderController' does not have a default constructor",
    "ExceptionType": "System.ArgumentException",
    "StackTrace": "   at System.Linq.Expressions.Expression.New(Type type)\r\n   at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, Func`1& activator)\r\n   at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)"
  }
}

My configuration is as follows and I am using the Unity.WebAPI library:

Startup.cs

    public void Configuration(IAppBuilder app)
    {
        HttpConfiguration config = GlobalConfiguration.Configuration;
        config.DependencyResolver = new UnityDependencyResolver(UnityConfig.GetConfiguredContainer());
        app.UseWebApi(WebApiConfig.Register());
        app.UseCors(CorsOptions.AllowAll);


        config.EnsureInitialized();

    }

UnityConfig.cs:

public static class UnityConfig
{
    #region Unity Container

    /// <summary>
    /// Load types in Unity Container 
    /// </summary>
    private static Lazy<IUnityContainer> container = new Lazy<IUnityContainer>(() =>
    {
        var container = new UnityContainer();
        RegisterTypes(container);
        return container;
    });

    /// <summary>
    /// Gets the configured Unity container.
    /// </summary>
    public static IUnityContainer GetConfiguredContainer()
    {
        return container.Value;
    }

    #endregion


    /// <summary>
    /// Register the types into Unity Container.
    /// </summary>
    /// <param name="container"></param>
    public static void RegisterTypes(UnityContainer container)
    {
        container.RegisterType<IProviderService, ProviderService();  
    } 
}

ProviderController.cs:

public class ProviderController : ApiController
{
    private static readonly ILog log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
    private readonly IProviderService providerService;      

    public ProviderController(IProviderService providerService)
    {
        providerService = providerService;
    }

    //Controller API Methods
}

ProviderService.cs:

    public ProviderService()
    {
        this.serviceClient = new ServiceClientAdapter();
    }

I have spent all morning reading through various threads and am unable to figure out where I am going wrong. If I remove Unity and instantiate a new ProviderService directly in the controller, everything works.

zaq · Accepted Answer · 2016-08-22 18:31:07Z

4

My problem was a small oversight. The call to UseWebApi in Startup.cs was not taking the HttpConfiguration config object as a parameter but was instead declaring it's own. This meant that WebAPI and Unity were configured with different HTTPConfiguration objects and the WebAPI was not aware of Unity as a result.

edited Aug 22, 2016 at 18:31

answered Aug 19, 2016 at 20:28

zaq

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2 Comments

Vasim Over a year ago

I think I might have similar problem. I tried injecting config object to DependencyResolver from startup class but didn't work! How were you able to resolve it?

zaq Over a year ago

If you look at my example above, for Startup.cs, the config object on the first line is used to configure Unity. Then when app.UseWebApi is called, a new config object is created and passed into it. This is the problem, the config declared on the first line should be passed in instead.

Vasim · Accepted Answer · 2016-12-16 22:54:55Z

1

Answer is already there! Just for easiness or shorter code.

You can write single method

    public static void RegisterComponents()
    {
        var container = new UnityContainer();

        // register all your components with the container here
        // it is NOT necessary to register your controllers

        container.RegisterType<IProviderService, ProviderService>();

        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }

Startup.cs:

    public void Configuration(IAppBuilder app)
    {
        ConfigureOAuth(app);
        HttpConfiguration config = GlobalConfiguration.Configuration;
        app.UseWebApi(config);
    }

Then add UnityConfig.RegisterComponents(); into Global file

edited Dec 16, 2016 at 22:54

answered Dec 16, 2016 at 22:49

Vasim

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