Question

I’m trying to write a EditorTemplate to generically apply CSS classes dependent upon logic provided in a helper passing the model and additional data from the ViewBag:

@using LSC.DCMP.Web.UI.Helpers
@model String

@ValidationFieldHelper.GetCSSClass(m => Model, @ViewBag.Step) 

This matches to a helper class that currently isn’t implemented, but has the following signature:

public static class ValidationFieldHelper
{
    public static object GetCSSClass(Func<object, string> func, object step)
    {
        throw new NotImplementedException();
    }
}

When I try to run the application, it fails compilation with the following error:

“Cannot use a lambda expression as an argument to a dynamically dispatched operation without first casting it to a delegate or expression tree type”.

I’ve read that lambda syntax isn’t fully supported using Razor templates so I’m unsure how I can implemented this functionality.

Answer 1

The issue is not to do with the lambda, but to do with the dynamic @ViewBag that you are using, which causes that statement to be dynamically dispatched, as mentioned in the error message.

Two other options to what Major Byte has offered:

1. Cast the dynamic which lets the compiler know what the dynamic will resolve to

   @ValidationFieldHelper.GetCSSClass(m => Model, (object)@ViewBag.Step)
   

2. Set the dynamic to a variable before using (basically the same deal as above)

   @{ object vstep = ViewBag.Step; }
   @ValidationFieldHelper.GetCSSClass(m => Model, vstep)
   

Both of these throw the correct exception for me.