Adding your own HtmlHelper in ASP.NET MVC 3

Question

I am new to MVC and I am trying to create my own extension method so that I can add onto the html helpers that are available in my razor views. Html.DropDownListFor() lets you create a drop down list for any propery on your model. I would like to create a helper called Html.StateDropDownListFor() that does the exact same thing, except loads the drop down with all 50 US states. This way I don't have to create a SelectList for every single state drop down that I create. What is the easiest way to do this? Right now I have this:

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(this HtmlHelper html)
    {
        // ???
    }
}

Am I even close? I don't want to rebuild a whole text box helper, I just want to create a helper that utilizes the existing text box helper but does the SelectList for me. That way in my views I could just do Html.StateDropDownList(x => x.State)

score 70 · Accepted Answer · edited Sep 11 '11 at 01:47

To use the custom helper method in your Razor views you will need to bring it into scope. There are two possible ways to do this:

Add a @using SomeNamespace in the top of your view with the namespace where the static class containing the helper is defined

In ~/Views/web.config, add:

<system.web.webPages.razor>
    <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        <pages pageBaseType="System.Web.Mvc.WebViewPage">
            <namespaces>
                <add namespace="System.Web.Mvc" />
                <add namespace="System.Web.Mvc.Ajax" />
                <add namespace="System.Web.Mvc.Html" />
                <add namespace="System.Web.Routing" />
                <add namespace="SomeNamspace" />
            </namespaces>
        </pages>
    </system.web.webPages.razor>

Once the custom helper is brought into scope in the view, Intellisense should be able to pick it and you could use it:

@Html.StateDropDownList()

Now you helper method needs to do something useful. You could either call existing helpers:

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(this HtmlHelper html)
    {
        return html.TextBox("foo")
    }
}

or return some custom data:

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(this HtmlHelper html)
    {
        return MvcHtmlString.Create("Hello world");
    }
}

If you have a strongly typed view and you wanted to use an expression:

using System.Web.Mvc;
using System.Web.Mvc.Html;

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(
        this HtmlHelper<MyViewModel> html
    )
    {
        var stateList = new SelectList(new[]
        {
            new { Key = "Alabama", Value = "Alabama" },
            new { Key = "Idaho", Value = "Idaho" },
            new { Key = "California", Value = "California" }
        }, "Key", "Value");
        return Html.DropDownListFor(
            x => x.State, stateList, "-- Select a state --"
        );
    }
}

and then:

@Html.StateDropDownList()

I think you misunderstand. I know how to use the extension method in my view. I just don't know what to do in the extension method to utilize the existing `TextBoxFor` helper in order to create my own helper, built off the existing helper. — CatDadCode, Feb 19 '11 at 18:49
Bingo, I was missing `using System.Web.Mvc.Html` and for whatever reason it wouldn't automatically resolve. Thanks! — CatDadCode, Feb 19 '11 at 18:57
I get a run-time error in HTML page because it is called with no argument, but the definition includes 1 which is **this HtmlHelper helper**. Do you know why? — Kevin Le - Khnle, Oct 15 '11 at 06:26
Where do you but your custom Html Helpers in your project ? as asked [here](http://stackoverflow.com/questions/1985436/where-to-put-my-custom-html-helpers) ? — Shaiju T, Nov 03 '15 at 14:28
@Khnle-Kevin - you need to include the model property it applies to: `@Html.StateDropDownListFor(m => m.State)` — tklives, Nov 23 '15 at 19:07

Bertrand Marron · Answer 2 · 2011-02-19T18:59:11.880

9

using System.Web.Mvc.Html;
public static MvcHtmlString StateDropDownList<TModel, TValue>( this HtmlHelper<TModel> html,
    Expression<Func<TModel, TValue>> expression ) {
        return html.DropDownListFor( expression, _stateList );
}

Would work. _stateList being an IEnumerable<SelectListItem>.

edited Feb 19 '11 at 18:59

answered Feb 19 '11 at 18:50

Bertrand Marron

21,501
8
58
94

1

This is closer, but `DropDownListFor` is not a property of `html` within the extension method context :/ – CatDadCode Feb 19 '11 at 18:53
2

Add a `using System.Web.Mvc.Html;` to make the extension methods available. – Andrew May 29 '12 at 04:09

score 0 · Answer 3 · answered Feb 13 '20 at 20:02

(Posted a solution on behalf of the question author, to move it to the answer section).

Here's the answer!

Here is the completed extension method in case anyone else ever has a use for it.

    public static MvcHtmlString StateDropDownListFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression)
    {
        Dictionary<string, string> stateList = new Dictionary<string, string>()
        {
            {"AL"," Alabama"},
            {"AK"," Alaska"},
            {"AZ"," Arizona"},
            {"AR"," Arkansas"},
            {"CA"," California"},
            {"CO"," Colorado"},
            {"CT"," Connecticut"},
            {"DE"," Delaware"},
            {"FL"," Florida"},
            {"GA"," Georgia"},
            {"HI"," Hawaii"},
            {"ID"," Idaho"},
            {"IL"," Illinois"},
            {"IN"," Indiana"},
            {"IA"," Iowa"},
            {"KS"," Kansas"},
            {"KY"," Kentucky"},
            {"LA"," Louisiana"},
            {"ME"," Maine"},
            {"MD"," Maryland"},
            {"MA"," Massachusetts"},
            {"MI"," Michigan"},
            {"MN"," Minnesota"},
            {"MS"," Mississippi"},
            {"MO"," Missouri"},
            {"MT"," Montana"},
            {"NE"," Nebraska"},
            {"NV"," Nevada"},
            {"NH"," New Hampshire"},
            {"NJ"," New Jersey"},
            {"NM"," New Mexico"},
            {"NY"," New York"},
            {"NC"," North Carolina"},
            {"ND"," North Dakota"},
            {"OH"," Ohio"},
            {"OK"," Oklahoma"},
            {"OR"," Oregon"},
            {"PA"," Pennsylvania"},
            {"RI"," Rhode Island"},
            {"SC"," South Carolina"},
            {"SD"," South Dakota"},
            {"TN"," Tennessee"},
            {"TX"," Texas"},
            {"UT"," Utah"},
            {"VT"," Vermont"},
            {"VA"," Virginia"},
            {"WA"," Washington"},
            {"WV"," West Virginia"},
            {"WI"," Wisconsin"},
            {"WY"," Wyoming"},
            {"AS"," American Samoa"},
            {"DC"," District of Columbia"},
            {"FM"," Federated States of Micronesia"},
            {"MH"," Marshall Islands"},
            {"MP"," Northern Mariana Islands"},
            {"PW"," Palau"},
            {"PR"," Puerto Rico"},
            {"VI"," Virgin Islands"},
            {"GU"," Guam"}
        };
        return html.DropDownListFor(expression, new SelectList(stateList, "key", "value"));
    }

I modified the code above to use a dictionary for state abbreviations.

Just don't forget to reference System.Web.Mvc.Html at the top of your extension method class like I forgot to.

Adding your own HtmlHelper in ASP.NET MVC 3

3 Answers3

Linked