Creating an Action (VB)

by Microsoft

Learn how to add a new action to an ASP.NET MVC controller. Learn about the requirements for a method to be an action.

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.vb

[!code-vbMain]

   1:  <HandleError()> _

   2:  Public Class HomeController

   3:      Inherits System.Web.Mvc.Controller

   4:   

   5:      Function Index() As ActionResult

   6:          Return View()

   7:      End Function

   8:   

   9:      Function SayHello() As String

  10:          Return "Hello!"

  11:      End Function

  12:  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.vb

[!code-vbMain]

   1:  Public Class WorkController

   2:      Inherits System.Web.Mvc.Controller

   3:   

   4:       _

   5:      Function CompanySecrets() As String

   6:          Return "This information is secret."

   7:      End Function

   8:   

   9:  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)

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