Is there a way to add a default view and a default controller in ASP.NET MVC 2?

Question

What I would really like to be able to do is redefine the conventions to do the following:

For Controllers and their respective Actions:

If a URL request is made, and there is not a controller with the supplied action, then perform some "default" function, which I would supply myself in the application. I would think this could be achieved by using a Func<>, but I'm not sure where to plug this in.

For Views:

If a controller's action is requesting for a View, and there is no View that matches the one that the controller's action is requesting for, return this "default" view.

Is this something that is possible, and if so where should I be digging in order to learn more about how to do this? Or is it a really simple thing to do?

EDIT

Here's an example of what I'm trying to achieve.

I have a very simplistic view, something akin to this:

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" 

Inherits="System.Web.Mvc.ViewPage<dynamic>" %>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
    <%: Html.LabelForModel() %>
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">

    <%: Html.EditorForModel() %>

</asp:Content>

So let's say I have a Customer class, and the controller action does something with a Customer object, and then does

return View(someCustomer);

The issue here, is that I have not defined any View to handle Customer. In this case, I want my view engine (or whatever is responsible), to say, "ok there's no view that directly handles Customers, I'll use the default view instead".

Answer 1

You could do it like this. I'm not sure of any performance implications or any other issues that might arise from capturing all 404s (including images and other content files)

protected void Application_Error(object sender, EventArgs e) {
    HttpException httpException = Server.GetLastError() as HttpException;
    if (httpException != null) {
        switch (httpException.GetHttpCode()) {
            case 404:
                //we couldn't find the controller or action

                //setup a new route to your default controller assigned
                //to handle unknown routes
                RouteData routeData = new RouteData();
                routeData.Values.Add("controller", "YourDefault");

                //create an instance of your controller and execute it
                IController yourDefaultController = new YourDefaultController();
                yourDefaultController.Execute(new RequestContext(
                        new HttpContextWrapper(Context), routeData));
                break;
        }
    }

}

Answer 2

Controllers & Actions

I think you might want to create a custom controller factory. I haven't done this myself, but it should be an easy google (touch wood).

Views

You should look into creating a custom view engine (or just extending the default view engine) to look for different the different default files.

HTHs,
Charles

Answer 3

You are asking for a number of different components.

First, create a 'DefaultController' with a 'Default' action.

To capture a request for a non existant controller, you need to override the controller factory:

protected override IController GetControllerInstance(System.Web.Routing.RequestContext requestContext, Type controllerType)
{
    try
    {
        return base.GetControllerInstance(requestContext, controllerType);
    }

    catch (HttpException ex)
    {
        int httpCode = ex.GetHttpCode();
        if(httpCode == (int)HttpStatusCode.NotFound)
        {
            IController controller = new DefaultController();
            ((DefaultController)controller).DefaultAction();
            return controller;
        }
        else
        {
            throw ex;
        }
    }
}

Then register this controller factory in the Global.asax startup.

To capture the case when an existing controller is called, but the action doesn't exist, override the HandleUnknownAction method, preferably in a base class:

public class BaseController : Controller
{
    protected override void HandleUnknownAction(string actionName)
    {
        RouteData.Values["action"] = "DefaultAction";

        if ( this.ActionInvoker.InvokeAction(this.ControllerContext, "DefaultAction"))
               return;

        base.HandleUnknownAction(actionName);
    }
}

Finally, to get a 'default'' view, you need to override the default view engine:

public class MyWebFormViewEngine : WebFormViewEngine
{
    public override ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache)
    {
        ViewEngineResult result = null;

        result = base.FindView(controllerContext, viewName, masterName, useCache);

        if (result == null || result.View == null)
           result = base.FindView(controllerContext, "Default", masterName, useCache);

        return result;
    }
}

and register this in your Global.asax:

protected void Application_Start()
{
    ViewEngines.Engines.Clear();
    ViewEngines.Engines.Add(new MyWebFormViewEngine());

    RegisterRoutes(RouteTable.Routes);
// etc
}

Hope that helps...

Answer 4

Why not solve controller/action problem with routing?

Routing can have constraints, right? So why not solve the problem with non existing controller/action using that?

routes.MapRoute(
    "Root",
    "",
    new { controller = "Home", action = "Index" }
);

routes.MapRoute(
    "Default",
    "{controller}/{action}/{id}",
    new { action = "Index", id = UrlParameter.Optional },
    // constraints for certain controllers (add actions if needed as well)
    new { controller = "Home|ControllerOne|ControllerTwo|..."}
);

// catch any request route and handle by the same controller/action
routes.MapRoute(
    "NonExisting",
    "{path*}",
    new { controller = "Default", action = "Any" }
);

Regarding views

If your controllers will always be caught, you shouldn't worry about views anyway. So if your last route resolves to anything and always displays the same content, it should never happen for a controller to request a non-existing view.

Edit about views (based on your comment)

If I understand the point of views in your comment, you will have to create a separate view engine that could solve everything by just providing an additional view path to an exact aspx file.

Default engine defines view paths with variables in them like Views/{0}/{1}.aspx. You could then add an additional line like Views/General/Default.aspx that would do the trick. Whe it will be searching for a particular view, it will match one if it exists but if it doesn't it will graciously fall down to default view.