ASP.NET MVC: Is a helper allowed to grab data?

Question

All my controllers in my project inherit from a base controller, which has a property with my Entity Model.

Let say I have a view that shows cities in the world, and it has an option to filter by country. The country filter is a dropdown list of countries from the database. The Html helper for the dropdown list requests a IEnumerable<SelectItem>.

Now with that info, is it ok if I create a HtmlHelper that looks like this:

    public static IEnumerable<SelectListItem> GetCountries(HtmlHelper htmlHelper)
    {
        return (from c in ((BaseController) htmlHelper.ViewContext.Controller).Entities.Countries
                orderby c.Name
                select new SelectListItem() {Text = c.Name, Value = c.ID});


    }

The question is not if I it is possible, but if it is ok according to the MVC way of doing things. (Or should I put the collection of countries in the ViewData inside the controller?)

Answer 1

I would pass the data as a parameter to the GetCountries method. The htmlHelper function really shouldn't know about the properties of your base controller - what if someone were to ever use it on a controller that doesn't inherit from your base? I know I know, you control the code, blah blah. If you're really interested in best practices, avoid the dependency.

public static IEnumerable<SelectListItem> GetCountries(this HtmlHelper html, Countries countries) {
    return from c in countries
           order by c.Name
           select new SelectListItem 
           {
               Text = c.Name,
               Value = c.ID
           };
}

then, in your View:

<%=Html.GetCountries(this.Entities.Countries)%>

Answer 2

Check out the ViewModel pattern, it's mentioned in the NerdDinner tutorial: http://nerddinnerbook.s3.amazonaws.com/Part6.htm

Basically you create a ViewModel class that encapsulates all the data you might need for your view. So you'd have a class that contains a list of all cities and/or countries, and whatever else, instantiated/populated in the controller action.

Then, you can strongly type your view to use that ViewModel class, and blammo: you've got all the data you need for your form.

Answer 3

I think html helper should return html. So you have two approaches:

first, if you want to do this as you started, from your htmlhelper prepare your list of elements and then call html.RenderDropDown with initialized list, selected element etc...

second, you can all prepare in your model, so controller will pass initiated object with all elements you need so in you view you can call renderdropdown directly

cheers