Asp.net-mvc – Use a legacy ASP.NET ASCX User Control in MVC Razor view

ascxasp.net-mvcwebforms

I am trying to implement a MVC Razor _Layout.cshtml page that uses a WebForm ascx User Control (non-MVC). I am doing this based off the "Yes" section of this Scott Hansleman article "Mixing Razor Views and WebForms Master Pages with ASP.NET MVC 3" http://www.hanselman.com/blog/MixingRazorViewsAndWebFormsMasterPagesWithASPNETMVC3.aspx

The article says how to use the same ascx User Control in both a webform Site.Master page as well as an MVC Razor _Layout page.

From what I've read elsewhere on Stackoverflow it is possible to use legacy ascx user controls (as well as ASP.NET webform server controls) in MVC pages. Using the following line should render the ascx user control in my Razor _Layout:

@{ Html.RenderPartial("~/UserControls/WebUserControl1.ascx"); }

However, that throws the error:

The view at '~/UserControls/WebUserControl1.ascx' must derive from ViewPage,
ViewPage<TModel>, ViewUserControl, or ViewUserControl<TModel>.

I have also tried the below with similar results:

@Html.Partial("~/UserControls/WebUserControl1.ascx")

What am I missing here?

Best Answer

As the error message states, the user control "must derive from ... ViewUserControl". In the code behind file for your user control, simply change this...

public partial class WebUserControl1 : UserControl
{
    // ...
}

... to this:

public partial class WebUserControl1 : ViewUserControl
{
    // ...
}

ViewUserControl inherits from UserControl, so it will continue to work in your existing WebForms pages.

You may have to deal with additional issues beyond this one in order to get your user control to work in MVC, though. At least one other that I encountered is (alluded to by SLaks):

Control 'controlId' of type 'controlType' must be placed inside a form tag with runat=server.

If you encounter stuff like this, you're going to have to get creative. Either modify the user control so that it can live happily in both WebForms and MVC (replace the offending controls with generic HTML equivalents - with all the implications of that), or duplicate it so you have a WebForms version and an MVC version.

For example, you will have to replace things like <asp:TextBox ID="search"> with <input type="text" name="search" />, which means you also need to modify the server-side code that handles the value coming from that input. Basically you have to neuter the user control, converting it from something that used to embody both view rendering logic and post-back handling logic, into something that just renders a view.

You can make one ascx control play nicely with both WebForms and Razor MVC, and for simple things like page headers and footers or read-only views of data this is a good approach for migrating an application to MVC. But for more complex things like input forms, it will probably be easier to maintain both an ascx user control and an MVC Razor view.

Related Solutions

Asp.net-mvc – the ‘page lifecycle’ of an ASP.NET MVC page, compared to ASP.NET WebForms

I'll attempt to comment on each of the bullet points you mentioned:

Your master pages still exist in MVC and are used to provide a consistent layout to the site. not much new there.

Your content pages will become views in the MVC world. They still provide the same content areas to your master pages.

The eventhandling of webforms should not be used in MVC, instead your Controller classes and their action methods will handle loading your data into a "model" that gets passed to the view.

Although webform style databinding is possible in MVC, I find that it is not the optimal solution. Better to place your data in a model class and strongly type your view so that you have direct access to that model. Then its simply a matter of using the <%= ViewData.Model.SomeProperty %> syntax to access your data and display it in the desired locations. As for viewstate, my recommendation is to forget that it even exists.

Remember that one of the advantages of using MVC is that you have control over the HTML you send to the client. Embrace that power and try to find solutions that allow you to maintain that control. Webform controls attempt to hide the the html from you and as such make it more difficult to customize the html when you need to.

I would highly recommend JQuery or one of the other similarly powerful javascript libraries. But learn to use them to access the HTML DOM directly and avoid the id mangling issues of webform controls.

You can use jquery to hook into the dropdown selection on the client side and submit standard or ajax style requests. Those request can return new pages, redirects, html fragments or even JSON data that can be used to update the existing page.

The asp.net Session can be used as needed.

Asp.net-mvc – How to render an ASP.NET MVC view as a string

Here's what I came up with, and it's working for me. I added the following method(s) to my controller base class. (You can always make these static methods somewhere else that accept a controller as a parameter I suppose)

MVC2 .ascx style

protected string RenderViewToString<T>(string viewPath, T model) {
  ViewData.Model = model;
  using (var writer = new StringWriter()) {
    var view = new WebFormView(ControllerContext, viewPath);
    var vdd = new ViewDataDictionary<T>(model);
    var viewCxt = new ViewContext(ControllerContext, view, vdd,
                                new TempDataDictionary(), writer);
    viewCxt.View.Render(viewCxt, writer);
    return writer.ToString();
  }
}

Razor .cshtml style

public string RenderRazorViewToString(string viewName, object model)
{
  ViewData.Model = model;
  using (var sw = new StringWriter())
  {
    var viewResult = ViewEngines.Engines.FindPartialView(ControllerContext,
                                                             viewName);
    var viewContext = new ViewContext(ControllerContext, viewResult.View,
                                 ViewData, TempData, sw);
    viewResult.View.Render(viewContext, sw);
    viewResult.ViewEngine.ReleaseView(ControllerContext, viewResult.View);
    return sw.GetStringBuilder().ToString();
  }
}

Edit: added Razor code.

Best Answer

Related Solutions

Asp.net-mvc – the ‘page lifecycle’ of an ASP.NET MVC page, compared to ASP.NET WebForms

Asp.net-mvc – How to render an ASP.NET MVC view as a string

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