Guy Burstein : WF4

WF/WCF using Visual Studio 2010 and .NET Framework 4 Training Kit

Guy Burstein — Tue, 19 May 2009 16:23:59 GMT

WF/WCF using Visual Studio 2010 and .NET Framework 4 Training Kit

The Microsoft WF/WCF using Visual Studio 2010 and .NET Framework 4 Training Kit includes presentations, hands-on labs, and demos. This content is designed to help you learn how to utilize the Visual Studio 2010 features and a variety of WF and WCF new features.

Learn basic workflow creation, hosting and running , and test-drive workflow development.
Get an introduction to workflow services, communication between workflows and content based correlation of workflow instances.
Use the flexibility of Flowchart workflow activities to implement non-sequential workflows.
Learn how to rehost the workflow designer in a WPF desktop application and customize it in several ways.
Learn how you can leverage some of the main WF and WCF monitoring features to track application execution and troubleshoot problems with services when necessary.
Learn how Service discovery allows you to locate services on the same subnet using ad hoc discovery, or using a proxy to establish connections with servers regardless of where they are.

This version of the training kit is compatible with Visual Studio 2010 Beta 1.

Download here.

WF 4.0: Long Running Custom Activities with Bookmarks and NativeActivity

Guy Burstein — Tue, 19 May 2009 15:40:19 GMT

WF 4.0: Long Running Custom Activities with Bookmarks and NativeActivity

This is another post in my WF 4.0: Custom Activities series. In a previous post I have talked about creating a code only custom activity that performs a simple task. In this post I’ll talk about creating a more complex activities that takes inputs from the calling program during their execution.

In the previous post WF 4.0: Code Only Custom Activities for Atomic Actions | CodeActivity, CodeActivity<T> I implemented the following activity for reading a string from the console.

public class ReadString2 : CodeActivity<string>
{
  protected override void Execute(CodeActivityContext context)
  {
    string value = Console.ReadLine();
    context.SetValue(Result, value);
  }
}

While this activity will perform the task it is meant to do, it is blocking the calling thread and bad for scalability. In addition to that It is bound to getting the value from the console only, and it is not generic enough to support another input methods.

Enter Bookmarks.

Using NativeActivity for Complex Activities

To create a long running activity, add a new item of type Workflow Element item to the project. Notice that the default activity inherits from CodeActivity.

public class ReadString3 : CodeActivity
{
  protected override void Execute(CodeActivityContext context)
  {
  }
}

To create complex activities such as long running activities, me need to change the base class and inherit from NativeActivity or NativeActivity<T>. In addition to that, there is a difference between the type of the parameter that the CodeActivity takes for the Execute method and the type that NativeActivity takes. Change the input parameter type from CodeActivityContext to ActivityExecutionContext.

public class ReadString3 : NativeActivity
{
  protected override void Execute(ActivityExecutionContext context)
  {
    throw new NotImplementedException();
  }
}

Enter Bookmarks

In previous versions of Windows Workflow Foundation we had the ExternalDataExchangeService and WorkflowQueue when we wanted to build a simple long running activity. In WF 4.0 this is much more simple to do using Bookmarks.

To use bookmarks we need to:

Create a named bookmark and Implement a callback method
Signal from the caller program

Register a Named Bookmak

The following activity registers a bookmark called “input” with a callback method called OnBookmarkCallback.

public class ReadString3 : NativeActivity
{
  OutArgument<string> name;
  public OutArgument<string> Name
  {
    get { return this.name; }
    set
    {
      ThrowIfOpen();
      this.name = value;
    }
  }
 
  protected override void Execute(ActivityExecutionContext context)
  {
    context.CreateNamedBookmark("input", new BookmarkCallback(this.OnBookmarkCallback));
  }
 
  void OnBookmarkCallback(ActivityExecutionContext context, Bookmark bookmark, object obj)
  {
    this.Name.Set(context, (string)obj);
  }
}

Signal the workflow from the caller program

In a previous post I have talked about the code that is needed to execute a workflow. Since we are now talking about long running workflows we will start with the default code that is generated for us when we create a new sequential workflow console application that uses the WorkflowInstance that lets know when the workflow instance is idle, and to resume a bookmark:

...
myInstance.Run();
 
//Get a string from the console and resume the bookmark called “input”
string input = Console.ReadLine();
myInstance.ResumeBookmark("input", input);
 
syncEvent.WaitOne();      
...       

The main program performs the input and delivers the value to the workflow. Using this approach:

The main program is flexible in how it wants to get values from the user and any other input source
The workflow becomes idle when it is waiting for the input and during that time not consuming any resources from the machine.

To query the available bookmarks in a workflow instance, we can use the following code:

IList bookmarks = myInstance.GetAllBookmarks();
foreach (BookmarkInfo info in bookmarks)
{
  Console.Write(info.BookmarkName);
}

Enjoy!

WF 4.0: Code Only Custom Activities for Atomic Actions | CodeActivity, CodeActivity

Guy Burstein — Tue, 19 May 2009 14:03:52 GMT

WF 4.0: Code Only Custom Activities for Atomic Actions | CodeActivity, CodeActivity<T>

This is another post in my WF 4.0: Custom Activities series. In this post I’ll talk about creating a code only custom activity that performs a simple task. I’ll also use input and output parameters and talk about activities that returns a single value.

A Simple Code Activity

Lets start by building a simple activity that outputs a certain string to the console. To to that, lets add a new item of type Workflow Element (under the Workflow node in the item templates).

Visual Studio adds a new code file (remember – this is a code-only activity) with a class that inherits from the abstract class System.Activities.CodeActivity.

public class OutputString : CodeActivity
{
  protected override void Execute(CodeActivityContext context)
  {
 
  }
}

To implement the logic of the atomic action, we just have to code it here. Notice that we don’t have to tell the runtime that the status of this activity is closed or something like this like we had to in WF 3.5.

public class OutputString : CodeActivity
{
  protected override void Execute(CodeActivityContext context)
  {
    Console.WriteLine("Hello world");
  }
}

After building the project, the new custom activity will appear in the Toolbox, and can be used in the workflow.

Adding Input Parameters to the Custom Activity

To add a new input parameter to the activity, we declare a InArgument<T> field and property where T is the type of the parameter.

public class OutputString : CodeActivity
{
  InArgument<string> name;
 
  public InArgument<string> Name
  {
    get { return name; }
    set {
      ThrowIfOpen();
      name = value;
    }
  }
 
  protected override void Execute(CodeActivityContext context)
  {
    Console.WriteLine("Hello,  " + this.Name.Get(context));
  }
}

Note that in the property setter implementation I am calling the base class’ ThrowIfOpen() method. This method throws an InvalidOperationException if the activity has already been prepared for execution and the value cannot be set.

Also note that in order to get the property value, we do not store the value in a private member in the class, but instead – we use the InArgument class and using the Get method passing it the activity context.

Output Parameters to Custom Activities

Lets create a simple activity that reads the name from the console.

public class ReadString : CodeActivity
{
  OutArgument<string> outputString;
 
  public OutArgument<string> Output
  {
    get { return outputString; }
    set {
      ThrowIfOpen();
      outputString = value;
    }
  }
 
  protected override void Execute(CodeActivityContext context)
  {
    string value = Console.ReadLine();
    context.SetValue(Output, value);
  }
}

Notice how the code required for an output argument is similar to the one required for an input argument. Also notice how we set the value back to the output value using the ActivityContext instance.

Activities with a Single Output Parameter - CodeActivity<T>

The above sample read a string from the console and placed the value in the output parameter. If this is the case we can also inherit from CodeActivity<T>:

public class ReadString2 : CodeActivity<string>
{
  protected override void Execute(CodeActivityContext context)
  {
    string value = Console.ReadLine();
    context.SetValue(Result, value);
  }
}

Inheriting from CodeActivity<T> makes it more simple to write a custom activity that has a single output parameter. It has additional benefits which I’ll talk about in a subsequent post.

Summary

In this post I talked about creating a code only custom activities that performs a simple task. I have also talked about input and output parameters.

WF 4.0: How to Execute a Worklflow (WorkflowInvoker vs WorkflowInstance)

Guy Burstein — Tue, 19 May 2009 12:14:40 GMT

WF 4.0: How to Execute a Worklflow (WorkflowInvoker vs WorkflowInstance)

Note: This post is based on Visual Studio 2010 Beta 1 which is the latest version available in the time of writing this post, so by the time this technology ships, there are probably things that will be slight different.

There are two ways to execute a workflow:

Using the WorkflowInstance class
Using the WorkflowInvoker class

Execute Workflows using WorkflowInstace

When you create a new Sequential Workflow Console Application, Visual Studio creates the basic code needed to execute the workflow inside the Main method:

static void Main(string[] args)
{
  AutoResetEvent syncEvent = new AutoResetEvent(false);
 
  WorkflowInstance myInstance = new WorkflowInstance(new Sequence1());
 
  myInstance.OnCompleted = delegate(WorkflowCompletedEventArgs e)
  {
    syncEvent.Set();
  };
 
  myInstance.OnUnhandledException = delegate(WorkflowUnhandledExceptionEventArgs e)
  {
    Console.WriteLine(e.UnhandledException.ToString());
    return UnhandledExceptionAction.Terminate;
  };
 
  myInstance.OnAborted = delegate(WorkflowAbortedEventArgs e)
  {
    Console.WriteLine(e.Reason);
    syncEvent.Set();
  };
 
  myInstance.Run();
 
  syncEvent.WaitOne();
 
}

1. A workflow instance is created and gets a reference to the root activity of the workflow. The WorkflowInstance class lets us control the running instance of the workflow and exposes several methods for this such as Run(), Abort(), Cancel(), Load(), Unload etc.

2. Since the workflow execution is scheduled to another thread, we need to block the main thread until the workflow is completed or terminated. To do this, we:

Create an AutoResetEvent initialized to false,
Set the event to true when the workflow is completed, and
In the main thread - wait for the workflow to complete before exiting the method.

3. In order to handle errors in the workflow such as exceptions or termination, in addition to handling the OnCompleted event, we are also handling the OnHandledException and OnAborted events. Note that when the workflow has an unhandled exception, the program can still decide how it wants to end the workflow execution, whether it is by aborting, cancelling or terminating the workflow. If the workflow is terminated, the OnCompleted event will also be raised.

Execute Workflows using WorkflowInvoker

WorkflowInvoker lets you invoke a workflow much more easily than the previous approach. It takes the instance of the workflow or activity to run and executes it synchronously.

WorkflowInvoker.Invoke(new Sequence1());

There are additional overloads of this method that takes parameters and a TimeSpan in which the workflow should complete within. I’ll talk in more details about passing parameters to workflow in a subsequent post, but in general this is all we have to know about WorkflowInvoker.

Choosing between WorkflowInstance and WorkflowInvoker

If you have a simple workflow that should run synchronously – use WorkflowInvoker. This is useful also in when unit testing workflows (more on this in a later post).

If you have a long running workflow that you want to control – persist, abort, cancel etc – use WorkflowInstance.

Enjoy!

WF 4.0: Building a Hello World Sequential Workflow

Guy Burstein — Tue, 19 May 2009 12:10:45 GMT

WF 4.0: Building a Hello World Sequential Workflow

Start Visual Studio 2010 Beta 1 and create a new Sequential Workflow Console Application.

After you click OK, visual studio creates the new projects and creates a new WF project, in which there are some things you should know about:

References:

System.Xaml – Now that there are several technologies based on Xaml, this is a new Assembly in .Net Framework 4.0 that contains Xaml services such as serialization.
System.Activities is the assembly that contains the implementation of WF 4.0, and as you can guess, the corresponding namespace is System.Activities and anything beneath it.
System.Activities.Design contains the designers for the activities and the designer re-hosting implementation. Since the new designer is based on WPF, you can also note references to WindowsBase, PresentationCode and PresentationFramework.
System.ServiceModel contains WCF implementation (as of .Net Framework 3.0) and now System.ServiceModel.Activities contains the activities used for Workflow Services (the integration between WF and WCF).

Sequence.xaml:

By default, workflows are created declaratively in WF 4.0 and represented in .xaml files with no code behind. If you open this file with an Xml editor, you will see it clearly.

<?xml version="1.0" encoding="utf-8" ?>
<p:Activity x:Class="HelloWorld.Sequence1"
          xmlns:p="http://schemas.microsoft.com/netfx/2009/xaml/activities"
          xmlns:s="clr-namespace:System;assembly=mscorlib"
          xmlns:sad="clr-namespace:System.Activities.Debugger;assembly=System.Activities"
          xmlns:sadx="clr-namespace:System.Activities.Design.Xaml;assembly=System.Activities.Design"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <p:Sequence sad:XamlDebuggerXmlReader.FileName="C:\...\HelloWorld\Sequence1.xaml">
 
    </p:Sequence>
</p:Activity>

The new WF Designer shows an empty sequence, representing an empty block of execution. Note the warning sign that says that the sequence has no child activities.

From the Procedural section in the Toolbox, drag the WriteLine Activity to the design surface.

Now, you get a warning that the Text property is not set. To set it, go the properties window, and open the Expression Editor. In WF 4.0 you use the Expression to set values to variables and parameters, and you can use either static values (like in this case) or VB. Yes! Expression are written in VB.

Type the text you want to display to the console and click OK.

Now, that the simple workflow is completed, you can use Ctrl + F5 to run it like you normally do.

Debugging a Workflow

The debugging experience when debugging a workflow in WF 4.0 is very similar to the debugging experience when using code. You can right click an activity the in designer and select Insert Breakpoint, or use F9 to do this.

Once you do this and run the workflow, the debugger highlights the current activity using a yellow border (similar to the yellow background for the current statement when debugging code).

Enjoy!