Is it possible to create a generic @helper method with Razor?

Question

I am trying to write a helper in Razor that looks like the following:

@helper DoSomething<T, U>(Expression<Func<T, U>> expr) where T : class 

Unfortunately, the parser thinks that <T is the beginning of an HTML element and I end up with a syntax error. Is it possible to create a helper with Razor that is a generic method? If so, what is the syntax?

Answer 1

This is possible to achieve inside a helper file with the @functions syntax but if you want the razor-style readability you are referring to you will also need to call a regular helper to do the HTML fit and finish.

Note that functions in a Helper file are static so you would still need to pass in the HtmlHelper instance from the page if you were intending to use its methods.

e.g. Views\MyView.cshtml:

@MyHelper.DoSomething(Html, m=>m.Property1) @MyHelper.DoSomething(Html, m=>m.Property2) @MyHelper.DoSomething(Html, m=>m.Property3) 

App_Code\MyHelper.cshtml:

@using System.Web.Mvc; @using System.Web.Mvc.Html; @using System.Linq.Expressions; @functions {     public static HelperResult DoSomething<TModel, TItem>(HtmlHelper<TModel> html, Expression<Func<TModel, TItem>> expr)     {         return TheThingToDo(html.LabelFor(expr), html.EditorFor(expr), html.ValidationMessageFor(expr));     } } @helper TheThingToDo(MvcHtmlString label, MvcHtmlString textbox, MvcHtmlString validationMessage) {     <p>         @label         <br />         @textbox         @validationMessage     </p> } ... 

Answer 2

No, this is not currently possible. You could write a normal HTML helper instead.

public static MvcHtmlString DoSomething<T, U>(     this HtmlHelper htmlHelper,      Expression<Func<T, U>> expr ) where T : class {     ... } 

and then:

@(Html.DoSomething<SomeModel, string>(x => x.SomeProperty)) 

or if you are targeting the model as first generic argument:

public static MvcHtmlString DoSomething<TModel, TProperty>(     this HtmlHelper<TModel> htmlHelper,      Expression<Func<TModel, TProperty>> expr ) where TModel : class {     ... } 

which will allow you to invoke it like this (assuming of course that your view is strongly typed, but that's a safe assumption because all views should be strongly typed anyways :-)):

@Html.DoSomething(x => x.SomeProperty)