C# 4 and .NET 4

1322 ❘ ChaPTer 44 windOws wOrkflOw fOundAtiOn 4
This control is bound to the Body property of the Retry activity, and the HintText defines the help text
shown when no child activity has been added to the control. The XAML also includes some styles that are
used to show the expanded or contracted version of the designer — this ensures that the activity works
the same way as the built-in activities. All of the code and XAML for this example is available in the
04_CustomActivities solution.
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Up to this point, the chapter has concentrated on activities but has not discussed workflows. A workflow
is simply a list of activities, and indeed a workflow itself is just another type of activity. Using this model
simplifies the runtime engine, because the engine just needs to know how to execute one type of object — that
being anything derived from the Activity class.
You’ve already seen the WorkflowExecutor class, which can be used to execute a workflow, but as
mentioned at the time, this is only one of the ways that a workflow can be executed. There are three
different options for executing workflows, and each has different capabilities. Before getting into the other
methods of executing workflows, we must delve into arguments and variables.
arguments and Variables
A workflow can be considered a program, and one of the facets of any programming language is the ability
to create variables, and pass arguments into and out of that program. Naturally, Workflow 4 supports both
constructs, and in this section we show you how you can define both arguments and variables.
To begin with, let’s assume that the workflow is processing an insurance policy, so a likely argument to
pass to the workflow would be the policy ID. In order to define an argument to a workflow, you need to go
into the Designer and click on the Arguments button on the bottom left. This brings up a list of arguments
defined for the workflow, as shown in Figure 44-12, and here you can also add your own.
figure 44-12
To define an argument, you need to specify the Name, Direction (which can be In, Out, or InOut) and the
data type for that argument. You can optionally specify a default value, which will be used if the argument
is not provided.
The direction of the argument is used to define whether the argument is expected as an input to the workflow,
as an output from the workflow, or in the case of the InOut direction, as both an input and output.
In the first section of this chapter, we described using the WorkflowInvoker class to execute a workflow. There
are several overrides of the Invoke method that can be used to pass arguments into the workflow. They are
passed as a dictionary of name/value pairs, where the name must match the argument’s name exactly — this
match is case sensitive. The code below is used to pass a PolicyId value into a workflow — the code for this
example is available in the 05_ArgsAndVars solution.
Dictionary parms = new Dictionary();
parms.Add("PolicyId", 123);
WorkflowInvoker.Invoke(new PolicyFlow(), parms);
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