C# – Creating objects using Unity Resolve with extra parameters

cnetprismunity-container

I'm using Prism, which gives be the nice Unity IoC container too. I'm new to the concept, so I haven't gotten my hands all around it yet. What I want to do now is to create an object using the IoC container, but passing an extra parameter too. Allow me to explain with an example..:

I have a class that takes a commands object. This is registered in the IoC container, so it will handle it nicely:

public class Person 
{
    public Person(IApplicationCommands commands) { .. }
    ..
}

Person person = _container.Resolve<Person>();

Now – I want to pass in another argument – e.g. the name of the person. However, I still want to use the IoC container to handle the resolving and hence get the other paramenters from the IoC container. But pass in the name as a "custom" parameter. Can this be done?

public class Person 
{
    public Person(IApplicationCommands commands, string name) { .. }
    ..
}

string name = "John"; 
Person person = _container.Resolve<Person>(name); // ....??

This example doesn't seem to work, but is there a way to make it work? Or does Unity IoC container require all parameters to be registered in the container before calling Resolve?

Best Answer

Can I pass constructor parameters to Unity's Resolve() method?

container.Resolve<IFoo>(new ParameterOverrides<Foo> { { "name", "bar" }, { "address", 42 } });"

Related Solutions

C# – Specify constructor for the Unity IoC container to use

Register it like this instead:

container.RegisterType<Person>(new InjectionConstructor());

You can add the LifetimeManager as well using an overload of the RegisterType method.

That said, when modeling for DI, your life will be much easier if you have unambiguous contructors (i.e. no overloaded constructors).

C# – Cannot Inject Dependencies into ASP.NET Web API Controller using Unity

Figured it out.

For ApiControllers, MVC 4 uses a System.Web.Http.Dispatcher.IHttpControllerFactory and System.Web.Http.Dispatcher.IHttpControllerActivator to create the controllers. If there is no static method to register what the implementation of these they are; when they are resolved, the mvc framework looks for the implementations in the dependency resolver, and if they are not found, uses the default implementations.

I got unity resolution of controller dependencies working by doing the following:

Created a UnityHttpControllerActivator:

public class UnityHttpControllerActivator : IHttpControllerActivator
{
    private IUnityContainer _container;

    public UnityHttpControllerActivator(IUnityContainer container)
    {
        _container = container;
    }

    public IHttpController Create(HttpControllerContext controllerContext, Type controllerType)
    {
        return (IHttpController)_container.Resolve(controllerType);
    }
}

Registered that controller activator as the implementation in the unity container itself:

protected void Application_Start()
{
    // code intentionally omitted

    IUnityContainer container = BuildUnityContainer();
    container.RegisterInstance<IHttpControllerActivator>(new UnityHttpControllerActivator(container));

    ServiceResolver.SetResolver(t =>
       {
         // rest of code is the same as in question above, and is omitted.
       });
}

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