Creating an Action (VB)

The goal of this tutorial is to explain how you can create a new controller action. You learn about the requirements of an action method. You also learn how to prevent a method from being exposed as an action.

Adding an Action to a Controller

You add a new action to a controller by adding a new method to the controller. For example, the controller in Listing 1 contains an action named Index() and an action named SayHello(). Both methods are exposed as actions.

Listing 1 – Controllers\HomeController.vb

<HandleError()> _
Public Class HomeController
    Inherits System.Web.Mvc.Controller

    Function Index() As ActionResult
        Return View()
    End Function

    Function SayHello() As String
        Return "Hello!"
    End Function
End Class

In order to be exposed to the universe as an action, a method must meet certain requirements:

• The method must be public.
• The method cannot be a static method.
• The method cannot be an extension method.
• The method cannot be a constructor, getter, or setter.
• The method cannot have open generic types.
• The method is not a method of the controller base class.
• The method cannot contain ref or out parameters.

Notice that there are no restrictions on the return type of a controller action. A controller action can return a string, a DateTime, an instance of the Random class, or void. The ASP.NET MVC framework will convert any return type that is not an action result into a string and render the string to the browser.

When you add any method that does not violate these requirements to a controller, the method is exposed as a controller action. Be careful here. A controller action can be invoked by anyone connected to the Internet. Do not, for example, create a DeleteMyWebsite() controller action.

Preventing a Public Method from Being Invoked

If you need to create a public method in a controller class and you don’t want to expose the method as a controller action then you can prevent the method from being invoked by using the <NonAction> attribute. For example, the controller in Listing 2 contains a public method named CompanySecrets() that is decorated with the <NonAction> attribute.

Listing 2 – Controllers\WorkController.vb

Public Class WorkController
    Inherits System.Web.Mvc.Controller

     _
    Function CompanySecrets() As String
        Return "This information is secret."
    End Function

End Class

If you attempt to invoke the CompanySecrets() controller action by typing /Work/CompanySecrets into the address bar of your browser then you’ll get the error message in Figure 1.

Figure 01: Invoking a NonAction method(Click to view full-size image)