Using @Html inside shared @helper in App_Code

Question

I am building a very basic MVC3 site while I learn and I am having difficulty with the following declarative Razor html helper.

Inside RMB.cshtml inside App_Code folder:

@helper ReplaceCrLf(string strText)
{
    @Html.Raw(Html.Encode(strText).Replace(Environment.NewLine, "<br />"));
}

Inside my index.cshtml view:

@RMB.ReplaceCrLf(Model.Post)

This gives me a null reference exception on Html in the helper, because it doesn't seem to know what it is. I can work around this by passing Html from the view to the helper, but I was wondering if there is another way for my shared html helpers to be able to reference Html without me having to pass it in to ever helper I write?

For completeness, here is the working workaround:

In RMB.cshtml in App_Code

@helper ReplaceCrLf(string strText, System.Web.Mvc.HtmlHelper Html)
{
    @Html.Raw(Html.Encode(strText).Replace(Environment.NewLine, "<br />"));
}

In index.cshtml view

@RMB.ReplaceCrLf(Model.Post, Html)

Based on this answer, it is currently a limitation of putting custom Helpers in AppCode folder. — Samuel Béliveau
– Samuel Béliveau, Commented Jul 13, 2011 at 13:37

BetterLateThanNever · Accepted Answer · 2021-04-28 12:11:52Z

42

+50

I add this to any .cshtml files in App_Code now.

// Using's are needed to ensure helpers function correctly.
@using System.Web.Mvc;
@using System.Web.Mvc.Html;
@using System.Web.Mvc.Routing;
@using System.Web.Mvc.Razor;
@functions {
    private static WebViewPage page { get { return PageContext.Page as WebViewPage; } } 
    private static System.Web.Mvc.HtmlHelper<dynamic> html { get { return page.Html; } }
    private static UrlHelper url { get { return page.Url; } }
    private static dynamic viewBag { get { return page.ViewBag; } }
}

EDIT: Have modified the helper variable names to lowercase as I have had some conflicts with the built-in helpers names. I have modified the HTML helper to be generic which allows the use of TextBoxFor etc helpers

This makes those wonderful helpers available to all @helper methods and functions in the file.

Many thanks to Neshta for the original concept!

Complete Example to answer the question:

In RMB.cshtml in the App_Code folder

@functions {
    public static WebViewPage page = (PageContext.Page as WebViewPage);
    public static HtmlHelper<object> html = page.Html;
}

@helper ReplaceCrLf(string strText)
{
    @html.Raw(html.Encode(strText).Replace(Environment.NewLine, "<br />"));
}

In View:

@RMB.ReplaceCrLf("line1\nline2") // No passing HtmlHelper

edited Apr 28, 2021 at 12:11

BetterLateThanNever

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answered Feb 8, 2016 at 12:14

Ryan Buddicom

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1 Comment

Ryan Buddicom Over a year ago

@Omid-RH I've declined the edit as I believe I explicitly put this namespace on HtmlHelper as there are conflicting classes with that name (From memory a generic and non-generic one) included by the prior using statements. If you can confirm this isn't the case you're welcome to propose the edit again and I will accept.

Imad Alazani · Accepted Answer · 2013-08-17 10:51:10Z

21

I used a workaround like following

@helper HtmlRaw(string s)
{
    @(new HtmlString(s))
}

@helper ReplaceCrLf(string strText)
{
    @HtmlRaw(HttpUtility
                        .HtmlEncode(strText)
                        .Replace(Environment.NewLine, "<br />"));
}

edited Aug 17, 2013 at 10:51

Imad Alazani

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answered Aug 14, 2012 at 8:25

Erdogan Kurtur

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Comments

Neshta · Accepted Answer · 2014-10-02 10:01:52Z

16

It is possible to get helpers from the PageContext:

var page = (WebViewPage) PageContext.Page;
var Url = page.Url;
var Html = page.Html;
var ViewBag = page.ViewBag;
// and so on

Usage (like standard helpers):

@Url.Action("Index", "Home")
@Html.Raw("some encoded string")

answered Oct 2, 2014 at 10:01

Neshta

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Comments

Community · Accepted Answer · 2017-05-23 10:31:26Z

7

Looks like helpers in App_Code work but you don't have access to standard MVC Html. helpers

see Razor: Declarative HTML helpers

edited May 23, 2017 at 10:31

CommunityBot

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answered Jul 13, 2011 at 13:28

Dave

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2 Comments

Treborbob Over a year ago

Darn it, that also eventually took me to the original blog where I saw how to do this in the first place. Here's looking forward to MVC4 then :(

Miguel Angelo Over a year ago

Hi! I have created an idea in ASP.NET user voice related to this: Support @helper ExtensionMethod(this HtmlHelper html) for views in APP_CODE... help is appreciated in making it come to the front-lines... Thanks!

Atabaki · Accepted Answer · 2013-08-17 09:08:08Z

2

Add second Parameter in your helper as bellow

@helper ReplaceCrLf(string strText,HtmlHelper<dynamic> html)
{
    @Html.Raw(html.Encode(strText).Replace(Environment.NewLine, "<br />"));
}

when you use this helper pass this.Html as second Parameter

answered Aug 17, 2013 at 9:08

Atabaki

211 bronze badge

Comments

Leniel Maccaferri · Accepted Answer · 2014-09-05 23:32:23Z

2

This should be enough:

var message = new HtmlString(toast.Message.Replace(Environment.NewLine, "<br />"))

No need to use Html.Raw().

answered Sep 5, 2014 at 23:32

Leniel Maccaferri

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1 Comment

SushiGuy Over a year ago

Confirmed, did it right in CSHTML <text>@(new HtmlString(ShortenedText))</text>

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