In .Net MVC, how do you access variables from URL Routing outside of the Action?

Question

I'm building a controller that other controllers can inherit (provide base functionality across site without repeating code):

public abstract class ApplicationController : Controller
{
    protected ApplicationController()
    {
       //site logic goes here
       //what is the value of agentID from the Action below??
    }
}

public class AgentController : ApplicationController
{
    public ActionResult Index(string agentID)
    {
        return View();
    }
}

The logic that applies to the entire site will go into the constructor of the ApplicationController class.

The problem is in that constructor I need to access the value in the parameter from the Action, in this case agentID (it will be the same across the entire site). Is there a way to read that value in?

Answer 1

There is, though you need to override the ControllerFactory. In your RegisterRoutes method in global.asax.cs, add this line:

public static void RegisterRoutes(RouteCollection routes) {
    // Route code goes here
    ControllerBuilder.Current.SetControllerFactory(typeof(MyControllerFactory));
}

And then define your MyControllerFactory class

public class MyControllerFactory : DefaultControllerFactory {
    public override IController CreateController(RequestContext requestContext, string controllerName) {
        // poke around the requestContext object here
        return base.CreateController(requestContext, controllerName);
    }
}

The requestContext object has all of the route data and values in it. You can use this to pass whatever you would like to the constructor of your controller.

Edit to add that this is how most of the popular Dependency Injectors (for example, StructureMap) work too.

Answer 2

Actions happen after constructors. The value doesn't exist (hasn't been bound) in a constructor. The route data might be known in the constructor, but the action data binding certainly will not have happened yet. You can't get this value with certainty until the action has been invoked.

Route data can be accessed inside the controller via:

ControllerContext.RouteData.Values

However, it is incorrect to suppose that agentID can only be bound to route data. In fact, it could come from a server variable, a form field, a query string parameter, etc. My advice would be to pass it explicitly wherever it is needed. If nothing else, it makes your unit tests better.

Answer 3

I figured out how to do it ... very similar to Craig Stuntz's answer, but the difference is in how you reach the RouteData.

Using ControllerContext.RouteData.Values does not work in a regular method used this way (it does from the original controller, but not from a base one like I built), but I did get to the RouteData by overriding the OnActionExecuting method:

    protected override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        string agentID = filterContext.RouteData.Values["agentID"].ToString();
        OtherMethodCall(agentID);
    }