C# 4 and .NET 4

OC286 ❘ ChaPTer 57 windOws wOrkflOw fOundAtiOn 3.0
activities using this example. When creating custom activities, you can simply construct a class within a
workflow project; however, it is preferable to construct your custom activities inside a separate assembly,
because the Visual Studio design time environment (and specifically workflow projects) will load activities
from your assemblies and can lock the assembly that you are trying to update. For this reason, you should
create a simple class library project to construct your custom activities within.
A simple activity such as the WriteLineActivity will be derived directly from the Activity base class.
The following code shows a constructed activity class and defines a Message property that is displayed
when the Execute method is called:
using System;
using System.ComponentModel;
using System.Workflow.ComponentModel;
namespace SimpleActivity
{
///
/// A simple activity that displays a message to the console when it executes
///
public class WriteLineActivity: Activity
{
///
/// Execute the activity — display the message on screen
///
///
///
protected override ActivityExecutionStatus Execute
(ActivityExecutionContext executionContext)
{
Console.WriteLine(Message);
}
return ActivityExecutionStatus.Closed;
///
/// Get/Set the message displayed to the user
///
[Description("The message to display")]
[Category("Parameters")]
public string Message
{
get { return _message; }
set { _message = value; }
}
///
/// Store the message displayed to the user
///
private string _message;
}
}
Within the Execute method, you can write the message to the console and then return a status of Closed to
notify the runtime that the activity has completed.
You can also define attributes on the Message property so that a description and category are defined for
that property. This is used in the property grid within Visual Studio, as shown in Figure 57-8.
The code for the activities created in this section is in the 03 CustomActivities solution. If you compile
that solution, you can then add the custom activities to the toolbox within Visual Studio by choosing
the Choose Items menu item from the context menu on the toolbox and navigating to the folder where the
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