ASP.NET MVC inline helper for fields

Question

I need a generic inline helper to show fields.

Here is what I have currently:

@helper DisplayField(Func<MyModel, string> field)
{
    if (string.IsNullOrWhiteSpace(field(Model)) == false)
    {
        <div class="row"> @field(Model) </div>     
    }
}

Usage:

@DisplayField(m => m.Name)
@DisplayField(m => m.PhoneNumber)

I have no idea how to show Label(DisplayAttribute) inside of a helper. Please help.

Answer 1

At the top of your page, add in a using for System.Linq.Expressions, eg.

@using System.Linq.Expressions

(or add this namespace in web.config).

Then to create the helper, it would look something like:

@helper DisplayField(Expression<Func<MyModel, string>> field)
{
    @Html.LabelFor(field)
    @Html.DisplayFor(field)
}

You can add extra logic in there to check for empty value etc. You may be better off creating an HtmlHelper though, that way you can use generic type arguments rather than "MyModel" and "string" as above. When I last tried it was not possible to add generic type arguments to an inline helper, eg. the following is not possible, unless this feature has since been added:

@helper DisplayField<TModel, TValue>(Expression<Func<TModel, TValue>> field)
{
    @Html.LabelFor(field)
    @Html.DisplayFor(field)
}

So, to get the generic method, you would use a custom HtmlHelper. To do this:

1. Create a file like the following:

   using System;
   using System.Linq;
   using System.Linq.Expressions;
   using System.Web;
   using System.Web.Mvc;
   using System.Web.Mvc.Html;
   
   namespace MvcApplication1.HtmlHelpers
   {
       public static class HtmlHelpers
       {
           public static MvcHtmlString DisplayFieldFor<TModel, TValue>(
               this HtmlHelper<TModel> helper, 
               Expression<Func<TModel, TValue>> field)
           {
               var labelString = helper.LabelFor(field);
               var displayString = helper.DisplayFor(field);
   
               return MvcHtmlString.Create(
                   labelString.ToString() + 
                   displayString.ToString());
           }
       }
   }
   

2. In your page, the usage of such a thing would be:

   @Html.DisplayFieldFor(m => m.Name)
   @Html.DisplayFieldFor(m => m.PhoneNumber)
   

etc. You may need to check your usings on your page or add the namespace for the HtmlHelper into web.config.