Question

I have an ASP.NET WebForms control (derived from Control, not WebControl, if it helps) that has a rather complicated Render() function. The control has no viewstate and only uses the Control approach so it can render output directly. I feel it’s a fine candidate for working with the MVC approach.

I’d like to use it in an MVC application I’m using, however I don’t know what’s the best way to go about it.

At first I thought about converting it to a HTML Helper method, but my control renders a large amount of HTML so the Helper method (with it returning strings) isn’t too attractive.

The alternative is a PartialView, but those are UserControl derivatives, which wouldn’t be appropriate in this case.

---

I see other HTML Helper methods don’t return HtmlString, but actually use HtmlHelper.ViewContext.Writer to write output directly, but according to this question ( HtmlHelper using ViewContext.Writer not rendering correctly ) he was getting strange results. I’d like to avoid that mishap.

---

EDIT:

I think I’ve solved it using the HtmlHelper.ViewContext.Writer approach, and I haven’t experienced the same problem as the problem I quoted.

Here’s the code I wrote:

public static class MiniViewHelper {

    public static void RenderMiniView<TModel>(this HtmlHelper html, MiniView<TModel> view, TModel model) {

        TextWriter wtr = html.ViewContext.Writer;
        HtmlTextWriter hwtr = wtr as HtmlTextWriter;
        if( hwtr == null ) hwtr = new HtmlTextWriter( wtr );

        view.Render( hwtr );
    }

}

public abstract class MiniView<TModel> {

    public TModel Model { get; set; }

    public abstract void Render(HtmlTextWriter wtr);

}

public class VeryComplicatedMiniView : MiniView<ComplicatedViewModel> {

    public override void Render(HtmlTextWriter wtr) {

        wtr.WriteLine("VeryComplicatedMiniView ");
    }

}

Used like so from my pages:

<% Html.RenderMiniView( new VeryComplicatedMiniView () { Propery1 = foo }, Model.RelevantMiniViewModel ); %>

Any thoughts?

Answer 1

The two approaches you have outlined in your question are correct. You could either try to write a custom HTML helper which will spit the same HTML as the control or use a partial.

I see other HTML Helper methods don’t return HtmlString, but actually
use HtmlHelper.ViewContext.Writer to write output directly

ViewContext.Writer should be fine. Returning an IHtmlString from the helper is also fine. Just make sure you are properly encoding it inside since IHtmlString will not be automatically HTML encoded in Razor and it supposes that the helper takes care of this. Using a TagBuilder to generate a DOM tree in a helper is a good approach.