为什么我不能在Razor函数部分使用Html.DisplayNameFor？

Question

This is two pieces of code:

This is my model:

public class EnrollRequest
{
    [Display(Name = "姓名")]
    public string Name { get; set; }

    [Display(Name = "性别")]
    public Gender? Gender { get; set; }

    // And other properties
}

I use this model for this page:

@model EnrollRequest

This one can pass compilation:

@{ 
    System.Linq.Expressions.Expression<Func<EnrollRequest, string>> exp = item => item.Name;
    Html.DisplayNameFor(exp);
}

But this one can't:

@functions
{
    public MvcHtmlString DisplayData<EnrollRequest, TValue>(System.Linq.Expressions.Expression<Func<EnrollRequest, TValue>> exp)
    {
        return DisplayDataTable(Html.DisplayNameFor(exp), Html.DisplayFor(exp));
    }
}

@helper DisplayDataTable(MvcHtmlString name, MvcHtmlString data)
{
    <tr>
        <th scope="row">@name</th>
        <td>@data</td>
    </tr>
}

It reports errors as follows on the first Html :

'HtmlHelper<EnrollRequest>' does not contain a definition for 'DisplayNameFor' and the best extension method overload 'DisplayNameExtensions.DisplayNameFor<EnrollRequest, TValue>(HtmlHelper<IEnumerable<EnrollRequest>>, Expression<Func<EnrollRequest, TValue>>)' requires a receiver of type 'HtmlHelper<IEnumerable<EnrollRequest>>'

It seems that it requires an IEnumerable as the model but I actually don't have. But the same call of Html.DisplayNameFor is valid in a helper. What's the problem?

===

Edit: I invoke DisplayData like this:

<table class="table">
    <tbody>
        @DisplayData(item => item.Name)

        @DisplayData(item => item.Gender)

        @DisplayData(item => item.School)

        @DisplayData(item => item.Grade)

        @DisplayData(item => item.Email)
    </tbody>
</table>

And it asks me to specify the generic type for DisplayData because it failed to auto detect it. Is there anything wrong?

Answer 1

I've found what my problem is:

public MvcHtmlString DisplayData<EnrollRequest, TValue>(System.Linq.Expressions.Expression<Func<EnrollRequest, TValue>> exp)
{
    return DisplayDataTable(Html.DisplayNameFor(exp), Html.DisplayFor(exp));
}

I accidentally wrote EnrollRequest in the generic types that actually it doesn't need. Just do this modification:

public MvcHtmlString DisplayData<TValue>(System.Linq.Expressions.Expression<Func<EnrollRequest, TValue>> exp)

Then everything works fine.

Hope this can help someone.