Injecting Dependency into Web API Controller

Question

I want to inject unity container into WebController.

I have UnityDependencyResolver:

public class UnityDependencyResolver : IDependencyResolver
{
    readonly IUnityContainer _container;

    public UnityDependencyResolver(IUnityContainer container)
    {
    this._container = container;
    }

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

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

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

Then, in my Global.asax I add the following line:

var container = new UnityContainer();
container.RegisterType<IService, Service>
(new PerThreadLifetimeManager()).RegisterType<IDALContext, DALContext>();
DependencyResolver.SetResolver(new UnityDependencyResolver(container));

Then, If I use the following in a Web Controller:

private IService _service;

public HomeController(IService srv)
{
    _service = srv;
}

It works fine.

But I want to inject it into WebAPI Controller, so if I do it the same way:

private IService _service;

public ValuesController(IService srv)
{
    _service = srv;
}

It does not work, it says that constructor is not defined. Ok, I create one more constructor:

public ValuesController(){}

And in this case it uses only this constructor and never the one where I should inject unity container.

Please advise.

Is this a WebAPI project or MVC app that happens to have an API controller. — jpgrassi, Jan 21 '16 at 20:15

smoksnes · Answer 1 · 2016-01-22T11:07:21.110

Add this in your WebApiConfig:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Routes and other stuff here...

        var container = IocContainer.Instance; // Or any other way to fetch your container.
        config.DependencyResolver = new UnityDependencyResolver(container);
    }
}

And if you want the same container you can keep it in a static variable, like so:

public static class IocContainer
{
    private static readonly Lazy<IUnityContainer> Container = new Lazy<IUnityContainer>(() =>
    {
        var container = new UnityContainer();
        return container;
    });

    public static IUnityContainer Instance
    {
        get { return Container.Value; }
    }
}

More info can be found here:

http://www.asp.net/web-api/overview/advanced/dependency-injection

On a sidenote, I can also recommend the nuget-package Unity.Mvc. It adds a UnityWebActivator and support for PerRequestLifetimeManager.

https://www.nuget.org/packages/Unity.Mvc/

Injecting Dependency into Web API Controller

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