Dynamic register controller in C# Web Api

Question

tl;dr: I'm creating Type (by reflection) that is extending ApiController. How can I dynamically register it (it can be registered at startup; no need to do this at runtime).

Long story:

So in my application I have multiple interfaces, i.e.:

interface IMyInterface
{
    MyResponse Hello(MyRequest request);
}

The thing that I want to achive is for each interface create controller that should look like this:

public class IMyInterfaceController : ApiController
{
    public IMyInterface MyInterface { get; set; }

    public MyResponse Hello([FromBody] MyRequest request)
    {
        return MyInterface.Hello(request);
    }
}

Generating this controller is already done using heavy C# reflection. The thing is that I want to do right now is to register this controller under /api/{controller}/{action}.

In Global.asax right now I got this:

public class MvcApplication : System.Web.HttpApplication
{
    private readonly InterfaceReader _reader = new InterfaceReader(); // this class is doing all staff with reflection to create controller class

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        WebApiConfig.Register(GlobalConfiguration.Configuration);
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);

        var controller = _reader.CreateController(new MyImplementation()); // MuImplementation implements IMyInterface
    }
}

MAGx2, could you please give a feedback if any of the provided solutions helped you? Marking the answer that worked for you may help other visitors in the future. — Anton
– Anton, Commented Jun 16, 2016 at 6:05

Anton · Accepted Answer · 2016-06-15 06:26:28Z

5

Solution with `IHttpControllerFactory`

I guess that what you need is a controller factory:

public class MyHttpControllerFactory : IHttpControllerFactory
{
    private readonly InterfaceReader _reader;
    private readonly HttpConfiguration _configuration;

    public MyHttpControllerFactory(InterfaceReader reader, HttpConfiguration configuration)
    {
        _reader = reader;
        _configuration = configuration;
    }

    public IHttpController CreateController(HttpControllerContext controllerContext, string controllerName)
    {
        if (controllerName == null)
        {
            throw new HttpException(404, string.Format("The controller for path '{0}' could not be found.", controllerContext.Request.RequestUri.AbsolutePath));
        }

        // Change the line below to whatever suits your needs.
        var controller = _reader.CreateController(new MyImplementation());
        controllerContext.Controller = controller;
        controllerContext.ControllerDescriptor = new HttpControllerDescriptor(configuration, controllerName, controller.GetType());

        return controllerContext.Controller;
    }

    public void ReleaseController(IHttpController controller)
    {
        // You may want to be able to release the controller as well.
    }
}

Then in the Global.asax you need to register the custom controller factory:

public class MvcApplication : System.Web.HttpApplication
{
    private readonly InterfaceReader _reader = new InterfaceReader(); // this class is doing all staff with reflection to create controller class

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        WebApiConfig.Register(GlobalConfiguration.Configuration);
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);

        GlobalConfiguration.Configuration.ServiceResolver.SetService(typeof(IHttpControllerFactory), new MyHttpControllerFactory(_reader, GlobalConfiguration.Configuration));
    }
}

Solution with `IHttpControllerActivator`

If you use Web Api 2 then the solution is to use either IDependencyResolver or IHttpControllerActivator instead of the factory. I guess that the IHttpControllerActivator is better option in your case.

public class MyServiceActivator : IHttpControllerActivator
{
    private readonly InterfaceReader _reader;
    private readonly HttpConfiguration _configuration;

    public MyServiceActivator(InterfaceReader reader, HttpConfiguration configuration)
    {
        _reader = reader;
        _configuration = configuration;
    }

    public IHttpController Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)
    {
        // Change the line below to whatever suits your needs.
        var controller = _reader.CreateController(new MyImplementation());
        return controller;
    }
}

Then in the Global.asax you need to register the custom activator:

public class MvcApplication : System.Web.HttpApplication
{
    // this class is doing all staff with reflection to create controller class
    private readonly InterfaceReader _reader = new InterfaceReader();

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        WebApiConfig.Register(GlobalConfiguration.Configuration);
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);

        HttpConfiguration config = GlobalConfiguration.Configuration;
        config.Services.Replace(typeof(IHttpControllerActivator), new MyServiceActivator(_reader, config));
    }
}

I hope this helps.

edited Jun 15, 2016 at 6:26

answered Jun 14, 2016 at 13:51

Anton

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6 Comments

MAGx2 Over a year ago

In method GetControllerInstance I got error because ApiController is not inheriting IController

Anton Over a year ago

@MAGx2 what I wrote before was suitable for MVC not WebApi, please see the updated answer.

MAGx2 Over a year ago

I do not have IHttpControllerFactory. As I see it was replaced stackoverflow.com/a/19640853/1819402

Anton Over a year ago

@MAGx2 , please see the updated answer once again. Hopefully the solution with IHttpControllerActivator is what you are looking for.

Royi Namir Over a year ago

Can you please paste a gist for InterfaceReader & MyServiceActivator ? we are in a situation where we need to create controller on the fly.

|

Fran · Accepted Answer · 2016-06-14 14:39:38Z

You need to create your own class that implements IHttpControllerActivator

Here's an example that I use for DI with Windsor

public class WindsorCompositionRoot : IHttpControllerActivator
{
    private readonly IWindsorContainer _container;

    public WindsorCompositionRoot(IWindsorContainer container)
    {
        _container = container;
    }

    public IHttpController Create(
        HttpRequestMessage request,
        HttpControllerDescriptor controllerDescriptor,
        Type controllerType)
    {
        var controller =
            (IHttpController) _container.Resolve(controllerType);

        request.RegisterForDispose(
            new Release(
                () => _container.Release(controller)));

        return controller;
    }

    private class Release : IDisposable
    {
        private readonly Action _release;

        public Release(Action release)
        {
            _release = release;
        }

        public void Dispose()
        {
            _release();
        }
    }
}

Then you need to wire it up in the Global.asax in Application_Start()

        Container = new WindsorContainer().Install(FromAssembly.This());

        GlobalConfiguration.Configuration.Services.Replace(
            typeof (IHttpControllerActivator),
            new WindsorCompositionRoot(Container));

Installing the controllers is done in a Windsor Installer class

public class ControllersInstaller : IWindsorInstaller
{
    public void Install(IWindsorContainer container, IConfigurationStore store)
    {
        container.Register(Classes.FromThisAssembly()
                            .BasedOn<IHttpController>()
                            .LifestyleTransient());
    }
}

In this example I don't see where my controllers are registered. Right now I cannot access them via /api/MyController/action.

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