Question

I originally created an editor template like this

@model MyModel
var items = // get items
@Html.DropDownListFor(m => m.Id, items, new { id = Html.IdFor(m => m) })

which was invoked by

@Html.EditorFor(m => m.SomeClass)

where SomeClass has an Id property. (The IdFor is one of my HTML helpers).

This would generate something like this

<select name="SomeClass.Id" id="SomeClass" />

Now I want to change the editor template into an HTML helper, so that my call looks like this

@Html.CustomEditorFor(m => m.SomeClass)

I’m changing this from a view to helper because its easier for reusability.

This is loosely what I have:

public static MvcHtmlString CustomEditorFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
{
    var idString = htmlHelper.IdFor(expression);
    var propertyValue = expression.Compile()(htmlHelper.ViewData.Model);
    var items = // get items
    return htmlHelper.DropDownListFor(expression, items, new {id = idString});
}

However, when I call the editor, I get this HTML instead of what I want.

<select name="SomeClass" id="SomeClass" />

How can I modify the expression enough to allow it to “access” the Id property?

Answer 1

Try this:

public static MvcHtmlString CustomEditorFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
{
    var idString = htmlHelper.IdFor(expression);
    var items = // get items

    var param = Expression.Parameter(typeof(TModel), "m");
    var member = Expression.Property(
                     Expression.Property(param, ExpressionHelper.GetExpressionText(expression))
                 , "Id");

    var isNullable = Nullable.GetUnderlyingType(member.Type);
    if (isNullable != null) {
        var expr2 = Expression.Lambda<Func<TModel, int?>>(
                        member, new[] { param }
                    );

        return htmlHelper.DropDownListFor(expr2, items, new { id = idString });
    }

    var expr = Expression.Lambda<Func<TModel, int>>(
                   member, new[] { param }
               );

    return htmlHelper.DropDownListFor(expr, items, new { id = idString });
}