C# 4 and .NET 4

1332 ❘ ChaPTer 44 windOws wOrkflOw fOundAtiOn 4
}
{
}
Branches =
{
new PickBranch
{
Variables = { roomName, width, depth },
Trigger = receiveRoomInfo,
Action = new WriteLine { Text = "Room Info Received"},
},
new PickBranch
{
Trigger = receiveDetailsComplete,
Action = new Sequence
{
Activities =
{
new Assign
{
To = new OutArgument(finished),
Value = new InArgument(true)
},
new WriteLine { Text = "Finished" }
}
}
}
}
Here, the While defines a Condition that evaluates the value of the finished variable. The Condition
property is defined as an Activity, so the ExpressionServices helper class is used to convert the
variable expression into an activity.
The Pick contains two branches, and the Trigger activity of each branch is what we are waiting for in
order to execute the Action activity. Building workflows in code is somewhat long-winded; however, we
believe it’s easier to see what is going on when you are learning Workflow 4 than using XAML-based
workflows. You might disagree!
hosting the designer
Often one wishes to save the best till last. We’d rather not break with tradition, so that’s what we’ve done
with this chapter. The Workflow Designer that is used within Visual Studio can also be hosted within
your own application, allowing your end users to create their own workflows without a copy of Visual
Studio in sight. This is, we believe, the best feature of Workflow 4 by far. Traditional application extension
mechanisms always require some form of developer — either to write an extension DLL and plug it into the
system somewhere, or by writing macros or scripts. Windows Workflow allows end users to customize an
application simply by dragging and dropping activities onto a design surface.
Rehosting the designer in Workflow 3.x was not for the faint-hearted; however, in Workflow 4 it becomes
almost trivial. The Designer itself is a WPF control, so we’ll use a WPF project as the main application.
The code for this example is available in the 08_DesignerRehosting project.
The first thing we need to do is to include the workflow assemblies, and then we need to define the main
window XAML. We always use the Model-View-ViewModel (MVVM) pattern when constructing WPF user
interfaces, as it simplifies the coding and also ensures that we can drape different XAML over the same view
model if necessary. The XAML for the main window is as follows:
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