As you may have heard Windows Workflow Foundation 4 is not an upgrade from Windows Workflow Foundation 3 (or 3.5). The version numbers might suggest that the previous version was quite mature but in fact it refers to the version of the .NET framework. In fact Windows Workflow Foundation 3 was the first version and 3.5 added only very few features and some bug fixes. And as WF 4 is a complete rewrite we should approach it as a new product and forget just about everything we already know about WF 3.
That might be a bit surprising, after all we still have activities and a workflow runtime right?
Well wrong actually!
There no longer is a class named WorkflowRuntime. Creating workflows is done by creating a WorkflowInstance object. This object is raises events for that workflow and only for that specific workflow.
But surely there is still an Activity base class?
Yes there is. But this is a completely new class that has nothing to do with the class Activity that was used with WF 3. In fact the new Activity class is in a new assembly and namespace, the full name is System.Activities.Activity in the assembly System.Activities.dll. The “old” activity class was System.Workflow.ComponentModel.Activity in the System.Workflow.ComponentModel.dll assembly. The old class still exists in .NET 4 so old workflows will still run but the new classes have no relation with the old classes.
So basically forget all you knew about the behavior of WF 3 [:(]
So lets take a brief look at creating a new workflow 4 style workflow.
When we start Visual Studio 2010 and select File/New/Project we get the new project tab. Select the Workflow node and you will see the four new project types
More about the different types in another blog post. For now just select the “Sequential Workflow Console Application”.
What we end up with is a simple project with just 2 files, the program.cs and the Sequence1.xaml. The latter contains the workflow. Note there is no choice between code or xaml workflows, the designer only works with xaml based workflows. Also note that the extension is no longer XOML but has changed to XAML.
The Sequence1.xaml workflow is still empty and looks like this:
When we open the Toolbox we see the new collection of basic activities. These are also completely new. For now just drag a WriteLine activity onto the Sequence in the designer. The goal of the WriteLine activity is just what the name suggest: write a line of text to some form of output stream. When we open the property sheet with the WriteLine activity selected we see there are just three properties: the DisplayName, the Text and the TextWriter.
The DisplayName is actually the name used on the design surface and used during the design of the workflow.
The Text property contains the text we want to print. In the property sheet we see a textbox with the text “<Enter an expression>”. This really is an expression editor where you can type in code. So if you want to enter a simple fixed text you must use quotation marks around it. This must always be a valid Visual Basic statement. yes that isn’t a typo Visual Basic, not C#, even if you are developing a C# project.
So in this case just add “Hello Workflow 4” including the quotation marks.
The TextWriter property is the text stream to write the text to. This is also an expression, just like the Text, and is optional. When not specified the text will be written to Console.Out which will do fine for now.
These expression windows in VB are completely new and a big change from WF3. Where we previously had to bind to property binding or something similar to add custom code we can now type it directly into the designer.
With this in place we are ready to run the workflow. Press Ctrl+F5 and with a bit of luck you should see the output appear in the console window. You might need a bit of luck because it appears the current bits are still a bit unstable and on my laptop running Windows 7 the designer tends to lock up quite a bit [:(]
In the next post more about how the workflow is created and started at runtime.