C# 4 and .NET 4

The Workflow runtime ❘ OC301
In Figure 57-18, we have selected the OrderDate property of a workflow (OrderDate is defined as a regular
.NET property on the workflow). Any bindable property can be bound to either a property of the workflow
that the activity is defined within or a property of any activity that resides in the workflow above the current
activity. Note that the data type of the property being bound must match the data type of the property you
are binding to — the dialog will not permit you to bind nonmatching types.
figure 57-18
The code for the Date property is shown here to show how binding works and is explained in the following
paragraphs:
public DateTime Date
{
get { return (DateTime)base.GetValue(DaysOfWeekActivity.DateProperty); }
set { base.SetValue(DaysOfWeekActivity.DateProperty, value); }
}
When you bind a property in the workflow, an object of type ActivityBind is constructed behind the
scenes, and it is this “value” that is stored within the dependency property. So, the property setter will
be passed an object of type ActivityBind, and this is stored within the dictionary of properties on this
activity. This ActivityBind object consists of data that describes the activity being bound to and the
property of that activity that is to be used at runtime.
When reading the value of the property, the GetValue method of the DependencyObject is called, and this
method checks the underlying property value to see if it is an ActivityBind object. If so, it resolves the
activity to which this binding is linked and then reads the real property value from that activity. If, however,
the bound value is another type, it simply returns that object from the GetValue method.
The WorKfloW runTime
In order to start a workflow, it is necessary to create an instance of the WorkflowRuntime class. This is
typically done once within your application, and this object is usually defined as a static member of the
application so that it can be accessed anywhere within the application.
When you start the runtime, it can then reload any workflow instances that were executing the last time the
application was executed by reading these instances from the persistence store. This uses a service called
the persistence service, which is defined in the following section.
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