C# 4 and .NET 4

OC302 ❘ ChaPTer 57 windOws wOrkflOw fOundAtiOn 3.0
The runtime contains six various CreateWorkflow methods that can be used to construct workflow
instances. The runtime also contains methods for reloading a workflow instance and enumerating all
running instances.
The runtime also has a number of events that are raised while workflows are executing — such
as WorkflowCreated (raised when a new workflow instance is constructed), WorkflowIdled (raised
when a workflow is awaiting input such as in the expense-processing example shown earlier), and
WorkflowCompleted (raised when a workflow has finished).
WorKfloW serViCes
A workflow doesn’t exist on its own. As described in the previous section, a workflow is executed within the
WorkflowRuntime, and this runtime provides services to running workflows.
A service is any class that may be needed while executing the workflow. Some standard services are provided
to your workflow by the runtime, and you can optionally construct your own services to be consumed by
running workflows.
This section describes two of the standard services provided by the runtime. It then shows how you can
create your own services and some instances of when this is necessary.
When an activity runs, it is passed some contextual information via the ActivityExecutionStatus
parameter of the Execute method:
protected override ActivityExecutionStatus Execute
(ActivityExecutionContext executionContext)
{
.
}
One of the methods available on this context parameter is the GetService method. This can be used as
shown in the following code to access a service attached to the workflow runtime:
protected override ActivityExecutionStatus Execute
(ActivityExecutionContext executionContext)
{
ICustomService myService = executionContext.GetService();
. Do something with the service
}
The services hosted by the runtime are added to the runtime prior to calling the StartRuntime method. An
exception is raised if you attempt to add a service to the runtime once it has been started.
Two methods are available for adding services to the runtime. You can construct the services in code and
then add them to the runtime by calling the AddService method. Or, you can define services within the
application configuration file, and these will be constructed for you and added to the runtime.
The following code snippet shows how to add services to the runtime in code — the services added are those
described later in this section:
using(WorkflowRuntime workflowRuntime = new WorkflowRuntime())
{
workflowRuntime.AddService(
new SqlWorkflowPersistenceService(conn, true, new TimeSpan(1,0,0),
new TimeSpan(0,10,0)));
workflowRuntime.AddService(new SqlTrackingService(conn));
.
}
Here are constructed instances of the SqlWorkflowPersistenceService, which is used by the runtime to
store workflow state, and an instance of the SqlTrackingService, which records the execution events of a
workflow while it runs.
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