How is Html helper 'available' to all views in MVC?

Question

Perhaps this is a question for Programmers - I'm sure someone will advise me if so.

When using MVC, I can also access the Html Helper variable and use whatever extension methods are defined, either the .Net ones or ones I might have specified myself.

@Html.Raw("<h1>This is my HTML</h1>")

How is this achieved? Say I wanted to add a separate object for another reason and have it available to all views in my MVC app?

I know I can't add it to the controller, as one view might be accessed by several controllers.

So my best guess is needing to subclass IView?

Edit: sorry - I didn't explain myself. At least I think...

I want the object to be available, but also instantiated. So for example, say I had an object called glosrob , with a method SayHello() and wanted to be able use it thusly:

@glosrob.SayHello()

Essentially I want to avoid having to add code to construct the object on each view eg avoid this

@{
    var glosrob = new Glosrob();
}

Answer 1

How is Html helper 'available' to all views in MVC?

Inside your views folder you will find a separate web.config file. In the config file will be the class that all views derive from:

<pages pageBaseType="System.Web.Mvc.WebViewPage">

So all views derive from WebViewPage class which contains a property called Html that exposes the HtmlHelper.

Say I wanted to add a separate object for another reason and have it available to all views in my MVC app?

If you want your own custom property exposed you should read up on Changing Base Type Of A Razor View .

First you create your own class with your own property:

public abstract class CustomWebViewPage : WebViewPage {
  public Glosrob Glosrob { get; set; }

  public override void InitHelpers() {
    base.InitHelpers();
    Glosrob = new Glosrob ();
  }
}

And update your config:

<pages pageBaseType="MyProject.Web.CustomWebViewPage">

Then you can call it in your view:

 @Glosrob.SomeMethod();

Answer 2

Inside your views folder you will find a separate web.config file. In this file you can declare namespaces that need to be imported. The section you're looking for is this:

<system.web.webPages.razor>
    <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" />
        </namespaces>
    </pages>
</system.web.webPages.razor>

If you want to import your own objects, you can add any namespace in this section and it will be available in your Razor views

EDIT: In case you need a specific instance for each view, you'll need to provide your own view implementation. You can do this by inheriting from WebViewPage:

public class MyViewPage : WebViewPage
{
    // implement property here
}

public class MyViewPage<TModel> : WebViewPage<TModel>
{
    // implement property here
}

Note that you need to provide an implementation for the generic AND non-generic version. After that you need to make sure that the View Engine uses this as the base page. In the section mentioned above you would do the following:

<system.web.webPages.razor>
    <pages pageBaseType="<the.name.space>.MyViewPage">
    ...
    </pages>
</system.web.webPages.razor>

In case you can do with a shared object, you could define it in a static class and make that class available using the above method.

Answer 3

Well you have a couple of options. You could put your Html Helper class in the System.Web.Mvc namespace like

    namespace System.Web.Mvc
{
    public static class HtmlExtensions
    {

You could also import the namespace on each page:

<%@ Import Namespace="MvcApplication1.Helpers" %>

Or you could register in the web.config

<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="MyHelper"/>

  </namespaces>

Also check this as a possible duplicate: Import Namespace for Razor View