Question

I need to render a partialview to a string, and I am trying to convert a C# example to VB.Net, as I am stuck with that for this project.

This is causing me a headache from these two problems:

1. ObjectViewData – I can’t figure out what that is
2. RenderPartial is a sub, but seems to be used as a function – I don’ get it

I reference the MVCContrib.UI, so I don’t need to convert that. But these two functions, I do need to convert:

(from brightmix.com)

/// Static Method to render string - put somewhere of your choosing
public static string RenderPartialToString(string userControl, object viewData, ControllerContext controllerContext)
{
    HtmlHelper h = new HtmlHelper(new ViewContext(controllerContext, new WebFormView("omg"), null, null), new ViewPage());
     var blockRenderer = new BlockRenderer(controllerContext.HttpContext);

     string s = blockRenderer.Capture(
         () => RenderPartialExtensions.RenderPartial(h, userControl, viewData)
     );

     return s;
 }

 /// Your Controller method...  
 public ActionResult MakeStringForMe()
 {
     var objectViewData = new objectViewData { SomeString = "Dude", SomeNumber = 1 };

     string s = RenderPartialToString("~/Views/Controls/UserControl.ascx", objectViewData, this.ControllerContext);

     View();
 }

Here is my attempt at converting it to VB.Net

'Static Method to render string - put somewhere of your choosing'
Public Shared Function RenderPartialToString(ByVal userControl As String, ByVal viewData As Object, ByVal controllerContext As ControllerContext) As String

    Dim h As New HtmlHelper(New ViewContext(controllerContext, New WebFormView("omg"), Nothing, Nothing), New ViewPage())

    Dim blockRenderer As New MvcContrib.UI.BlockRenderer(controllerContext.HttpContext)

    Dim s As String = blockRenderer.Capture(RenderPartialExtensions.RenderPartial(h, UserControl, viewData))

End Function

Public Function MakeStringForMe() As ActionResult

    Dim objectViewData As objectViewData = New objectViewData With {.SomeString = "Dude", .SomeNumber = 1}
    Dim s As String = RenderPartialToString("~/Views/Controls/UserControl.ascx", objectViewData, Me.ControllerContext)
    View()
End Function

Answer 1

This line:

Dim s As String = blockRenderer.Capture(RenderPartialExtensions.RenderPartial(h, UserControl, viewData))

is NOT equivalent to your original line:

string s = blockRenderer.Capture(
         () => RenderPartialExtensions.RenderPartial(h, userControl, viewData)
     );

The C# example is using a lambda, while the VB example is just calling the method directly, which doesn’t return a value. The compiler isn’t lying to you.

Try this instead:

Dim s = blockRender.Capture(New Action(Of String)(Function() RenderPartialExtensions.RenderPartial(h, UserControl, viewData)))

I took a look at Capture and it’s expecting an Action which is just a delegate, and it looks like the compiler can’t infer the delegate’s signature to wrap the anonymous function. So we’ll give it a helping hand and wrap the lambda ourselves.