The CodeActivity

We have open project from last post Refactoring Workflows as we seen on it, WF4 consists of a designer that edits .xaml files and a runtime that invokes activities. When we author a workflow, we are creating a new kind of activity and because activities are just classes that inherit from System.Activities.Activity or one of its subclasses, we can declare workflows using C#, VB or XAML. In this post, we will implement our “greeting” business process by creating an activity in C# or VB.
We will create an activity in code and write the text to the console using Console.WriteLine.

1. Right-click the HelloWorkflow project, point to Add and click Class. Type SayHelloInCode in the Name box.
2. Add the following namespace directives to the file.
   
   C#
   using System.Activities;
   
   
   Visual Basic
   Imports System.Activities
3. CodeActivity is an abstract class. That means that when we inherit from it, we must override the Execute method. This is the place where we will do the work of our activity. Replace the default implementation of the class with the following code.
   
   C#
   public class SayHelloInCode : CodeActivity
   {
     protected override void Execute(CodeActivityContext context)
     {
       Console.WriteLine("Hello Workflow 4 in code");
     }
   }
   
   
    (Code Snippet - Introduction to WF Lab - SayHelloInCode Class VB)
   Visual Basic
   Public Class SayHelloInCode

     Inherits CodeActivity

     Protected Overrides Sub Execute(ByVal context As CodeActivityContext)

       Console.WriteLine("Hello Workflow 4 in code")

     End Sub

   End Class
4. Change Program.cs (C#) or Module1.vb (Visual Basic) to use the new SayHelloInCode class. To do this, locate the WorkflowInvoker.Invoke method code, and replace it with the following code:
   
   C#
   static void Main(string[] args)

   {

     WorkflowInvoker.Invoke(new SayHelloInCode());

   }
   
   
   Visual Basic
   Shared Sub Main(ByVal args() As String)

     WorkflowInvoker.Invoke(New SayHelloInCode())

   End Sub
5. Press CTRL+F5 to run the workflow without debugging. The application should run in a console window and print the message “Hello Workflow 4 in code".
   

   

   The completed HelloWorkflow application

Note: Why would I create a code activity?

Writing business logic in code is nothing new. Why would we go to the effort to write it in a special class that inherits from CodeActivity? The reason is that by doing so now our business logic can be composed into other larger business processes that use the workflow runtime. As we will see later in the next posts it will also benefit from a model for threading and data management that provides for highly scalable and long running business applications.