Understanding the Workflow Runtime Engine
A single .NET assembly can define multiple workflow instances. Furthermore, you can easily build workflow
*.dlls that enable you to reuse workflows across multiple projects or .NET languages. You must inform the
WF runtime engine which workflow instance to execute and when.
From a high level, a WF-enabled application consists of the following:
• A workflow instance and the activities that represent it.
• An instance of the workflow runtime engine, which will execute the workflow instance.
• An application domain to host the runtime (only one runtime object per AppDomain).
The WF API has been designed to be as modular as possible. If required, your WF-enabled application could
bundle the workflow instance, runtime, and hosting logic within a single .NET executable. On the other hand,
each aspect of a WF-enabled application could be placed in reusable .NET assemblies. In any case, the high-
level composition of a WF application looks like this:
The WorkflowRuntime class represents the WF engine itself. This type is within the System.Workflow.
Runtime namespace of the System.Workflow.Runtime.dll assembly.
The WorkflowRuntime type provides only one property of any real interest. The IsStarted property allows
you to determine if a WorkflowRuntime has started to execute.
The WorkflowRuntime type defines a number of events that allow you to intercept various states of runtime
execution. Here are some key events of WorkflowRuntime, many of which you will see during your lab time.
In addition, WorkflowRuntime defines a set of interesting methods. You will see some of these members at
work throughout this class. Note that some of these members allow you to add or remove any of the WF
services examined earlier in this chapter (persistence, tracking, transactions, and so on). Others allow you to
enumerate / locate workflow instances hosted by the current runtime.
Hosting the WF Runtime within a Console Application
When you create a console-based WF app, the Main() method contains the necessary logic used to host the
initial workflow instance. The WorkflowInstance class represents the workflow instance to execute within
the engine.
In C#, the initial code looks like the following. The use of the AutoResetEvent logic simply ensures that the
console remains open until the WF has completed. Also notice that the boilerplate code has hooked into two
WF engine events by using C# anonymous method syntax.
// C#
static void Main(string[] args)
{
// Create the WF runtime.
using(WorkflowRuntime workflowRuntime = new WorkflowRuntime())
{
// Hook into WorkflowCompleted / WorkflowTerminated events.
AutoResetEvent waitHandle = new AutoResetEvent(false);
workflowRuntime.WorkflowCompleted
+= delegate(object sender, WorkflowCompletedEventArgs e)
{waitHandle.Set();};
workflowRuntime.WorkflowTerminated
+= delegate(object sender, WorkflowTerminatedEventArgs e)
{
Console.WriteLine(e.Exception.Message);
waitHandle.Set();
};
// Create an instance of the WF to execute and call Start().
WorkflowInstance instance =
workflowRuntime.CreateWorkflow(typeof(SimpleWFApp.Workflow1));
instance.Start();
waitHandle.WaitOne();
}
}
In VB, the WorkflowComplete / WorkflowTerminated events are handled via AddHandler statements. This
code would be located within the project’s Module1.vb file.
' VB
Module Module1
Class Program
Shared WaitHandle As New AutoResetEvent(False)
Shared Sub Main()
Using workflowRuntime As New WorkflowRuntime()
AddHandler workflowRuntime.WorkflowCompleted,
AddressOf OnWorkflowCompleted
AddHandler workflowRuntime.WorkflowTerminated,
AddressOf OnWorkflowTerminated
Dim workflowInstance As WorkflowInstance
workflowInstance =
workflowRuntime.CreateWorkflow(GetType(Workflow1))
workflowInstance.Start()
WaitHandle.WaitOne()
End Using
End Sub
' Targets for events.
Shared Sub OnWorkflowCompleted(ByVal sender As Object, _
ByVal e As WorkflowCompletedEventArgs)
WaitHandle.Set()
End Sub
Shared Sub OnWorkflowTerminated(ByVal sender As Object, _
ByVal e As WorkflowTerminatedEventArgs)
Console.WriteLine(e.Exception.Message)
WaitHandle.Set()
End Sub
End Class
End Module
When you want to host the workflow runtime within other applications, such as a Windows Forms or WPF
application, you will author similar code manually. To maximize reuse, you may wish to build a custom class
type that encapsulates the details of the runtime plumbing and place it in a dedicated .NET code library. You
will examine various ways to do so after your first lab.
A single .NET assembly can define multiple workflow instances. Furthermore, you can easily build workflow
*.dlls that enable you to reuse workflows across multiple projects or .NET languages. You must inform the
WF runtime engine which workflow instance to execute and when.
From a high level, a WF-enabled application consists of the following:
• A workflow instance and the activities that represent it.
• An instance of the workflow runtime engine, which will execute the workflow instance.
• An application domain to host the runtime (only one runtime object per AppDomain).
The WF API has been designed to be as modular as possible. If required, your WF-enabled application could
bundle the workflow instance, runtime, and hosting logic within a single .NET executable. On the other hand,
each aspect of a WF-enabled application could be placed in reusable .NET assemblies. In any case, the high-
level composition of a WF application looks like this:
The WorkflowRuntime class represents the WF engine itself. This type is within the System.Workflow.
Runtime namespace of the System.Workflow.Runtime.dll assembly.
The WorkflowRuntime type provides only one property of any real interest. The IsStarted property allows
you to determine if a WorkflowRuntime has started to execute.
The WorkflowRuntime type defines a number of events that allow you to intercept various states of runtime
execution. Here are some key events of WorkflowRuntime, many of which you will see during your lab time.
In addition, WorkflowRuntime defines a set of interesting methods. You will see some of these members at
work throughout this class. Note that some of these members allow you to add or remove any of the WF
services examined earlier in this chapter (persistence, tracking, transactions, and so on). Others allow you to
enumerate / locate workflow instances hosted by the current runtime.
Hosting the WF Runtime within a Console Application
When you create a console-based WF app, the Main() method contains the necessary logic used to host the
initial workflow instance. The WorkflowInstance class represents the workflow instance to execute within
the engine.
In C#, the initial code looks like the following. The use of the AutoResetEvent logic simply ensures that the
console remains open until the WF has completed. Also notice that the boilerplate code has hooked into two
WF engine events by using C# anonymous method syntax.
// C#
static void Main(string[] args)
{
// Create the WF runtime.
using(WorkflowRuntime workflowRuntime = new WorkflowRuntime())
{
// Hook into WorkflowCompleted / WorkflowTerminated events.
AutoResetEvent waitHandle = new AutoResetEvent(false);
workflowRuntime.WorkflowCompleted
+= delegate(object sender, WorkflowCompletedEventArgs e)
{waitHandle.Set();};
workflowRuntime.WorkflowTerminated
+= delegate(object sender, WorkflowTerminatedEventArgs e)
{
Console.WriteLine(e.Exception.Message);
waitHandle.Set();
};
// Create an instance of the WF to execute and call Start().
WorkflowInstance instance =
workflowRuntime.CreateWorkflow(typeof(SimpleWFApp.Workflow1));
instance.Start();
waitHandle.WaitOne();
}
}
In VB, the WorkflowComplete / WorkflowTerminated events are handled via AddHandler statements. This
code would be located within the project’s Module1.vb file.
' VB
Module Module1
Class Program
Shared WaitHandle As New AutoResetEvent(False)
Shared Sub Main()
Using workflowRuntime As New WorkflowRuntime()
AddHandler workflowRuntime.WorkflowCompleted,
AddressOf OnWorkflowCompleted
AddHandler workflowRuntime.WorkflowTerminated,
AddressOf OnWorkflowTerminated
Dim workflowInstance As WorkflowInstance
workflowInstance =
workflowRuntime.CreateWorkflow(GetType(Workflow1))
workflowInstance.Start()
WaitHandle.WaitOne()
End Using
End Sub
' Targets for events.
Shared Sub OnWorkflowCompleted(ByVal sender As Object, _
ByVal e As WorkflowCompletedEventArgs)
WaitHandle.Set()
End Sub
Shared Sub OnWorkflowTerminated(ByVal sender As Object, _
ByVal e As WorkflowTerminatedEventArgs)
Console.WriteLine(e.Exception.Message)
WaitHandle.Set()
End Sub
End Class
End Module
When you want to host the workflow runtime within other applications, such as a Windows Forms or WPF
application, you will author similar code manually. To maximize reuse, you may wish to build a custom class
type that encapsulates the details of the runtime plumbing and place it in a dedicated .NET code library. You
will examine various ways to do so after your first lab.
Workflow Runtime Engine
Table of Contents
Copyright (c) 2008. Intertech, Inc. All Rights Reserved. This information is to be used exclusively as an
online learning aid. Any attempts to copy, reproduce, or use for training is strictly prohibited.
online learning aid. Any attempts to copy, reproduce, or use for training is strictly prohibited.
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