Can't inject on System.Web.Http.Filters.ActionFilterAttribute using Unity bootstrapper for ASP.NET Web API nuget package

Question

I can't get dependency injection working with a custom ActionFilterAttribute class using the Unity bootstrapper for ASP.NET Web API nuget package.

I've registered the type in UnityConfig and I'm using it elsewhere (using constructor injection there though) and it works fine.

public static void RegisterTypes(IUnityContainer container)
{
    container.RegisterType<ISettingService, SettingService>();
    ...
}

The code is being called successfully, however the instantiated object (settingService) is null.

public class APIKeyValidationAttribute : ActionFilterAttribute
{
    [Dependency]
    public ISettingService settingService { get; set; }

public override void OnActionExecuting(HttpActionContext actionContext)
{
    ...
    if (settingService == null)
    {
        throw new Exception("settingService is null");
    }
    ...
}

What do I need to do to get this working? I've been searching for a long time and can only find examples for MVC or for Web API with different dependency injectors.

Randy Levy · Accepted Answer · 2014-08-06 20:15:14Z

11

First create an IFilterProvider that will perform a BuildUp and inject the dependencies:

public class UnityActionFilterProvider 
    : ActionDescriptorFilterProvider, IFilterProvider
{
    private readonly IUnityContainer container;

    public UnityActionFilterProvider(IUnityContainer container)
    {
        this.container = container;
    }

    public new IEnumerable<FilterInfo> GetFilters(
        HttpConfiguration configuration, 
        HttpActionDescriptor actionDescriptor)
    {
        var filters = base.GetFilters(configuration, actionDescriptor);

        foreach (var filter in filters)
        {
            container.BuildUp(filter.Instance.GetType(), filter.Instance);
        }

        return filters;
    }
}

Then register the IFilterProvider:

private static void RegisterFilterProviders()
{
    var providers = 
        GlobalConfiguration.Configuration.Services.GetFilterProviders().ToList();

    GlobalConfiguration.Configuration.Services.Add(
        typeof(System.Web.Http.Filters.IFilterProvider),
        new UnityActionFilterProvider(UnityConfig.GetConfiguredContainer()));

    var defaultprovider = providers.First(p => p is ActionDescriptorFilterProvider);

    GlobalConfiguration.Configuration.Services.Remove(
        typeof(System.Web.Http.Filters.IFilterProvider), 
        defaultprovider);
}

I put this method and invoked it in the UnityWebApiActivator class.

edited Aug 6, 2014 at 20:15

answered Oct 2, 2013 at 8:26

Randy Levy

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6 Comments

Michael Szabo Over a year ago

Thanks heaps Tuzo. I have created a new class, added the RegisterFilterProviders method into the UnityWebApiActivator class add added the namespace for the new class. This error is produced 'System.Collections.Generic.IEnumerable<System.Web.Http.Filters.IFilterProvider>' does not contain a definition for 'ToList' and no extension method 'ToList' accepting a first argument of type 'System.Collections.Generic.IEnumerable<System.Web.Http.Filters.IFilterProvider>' could be found (are you missing a using directive or an assembly reference?) is there any other namespaces that I need to add in?

Randy Levy Over a year ago

@MichaelS: ToList() is an extension method in System.Linq. Add using System.Linq; to the top of your file to resolve that compile error.

Michael Szabo Over a year ago

Thanks that worked fine. For some reason there was no "Resolve" option when I right clicked on it.

Fabio Milheiro Over a year ago

Very useful! @Tuzo, where did you come up with this stuff? I'd like to have a read myself. Thank you!

M005 Over a year ago

@RandyLevy I have tried your solution but for me, ISettingService is always null, can you help me?

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