Datasheet

Chapter 1: Workﬂ ow Programming Principles

Now let ’ s walk through the implementation of the Activity_Closed event handler. This event handler

first removes itself from the list of event handlers registered for the Closed event of the new copy of the

child activity of the WhileActivity activity:

e.Activity.Closed -= this.Activity_Closed;

Next, it casts its first argument to the ActivityExecutionContext type. Keep in mind that this

ActivityExecutionContext object represents the global activity execution context:

ActivityExecutionContext executionContext =

sender as ActivityExecutionContext;

It then accesses the ActivityExecutionContextManager object that manages the child execution context

that the WhileActivity activity creates and invokes the GetExecutionContext method on this object,

passing in the reference to the new copy of the child activity of the WhileActivity activity, to return a

reference to the ActivityExecutionContext object that represents the child execution context:

ActivityExecutionContext childExecutionContext =

executionContext.ExecutionContextManager.GetExecutionContext(e.Activity);

Next, it calls the CompleteExecutionContext method on the same ActivityExecutionContextManager

object, passing in the ActivityExecutionContext object that represents the child execution context, to

complete and to consequently discard the child execution context:

executionContext.ExecutionContextManager.CompleteExecutionContext(

childExecutionContext);

Finally, it checks whether the condition is met again. If so, it repeats the same steps discussed earlier to

deep copy the child activity of the WhileActivity activity and all its descendant activities once again,

create a new child execution context, and schedule the Execute method of the new copy of the child

activity for execution.

Developing Custom Conditions

As you saw, the WhileActivity activity exposes a property named Condition, which is of the

ActivityCondition type. You must assign an ActivityCondition object to this property before executing

the WhileActivity activity. The WhileActivity activity invokes the Evaluate method on this

ActivityCondition object at the beginning of every iteration to determine whether to execute the iteration

or complete its execution. Recall that the ActivityCondition is an abstract class. Every activity condition

must inherit from this abstract base class or one of its subclasses.

In this section we ’ ll develop a custom condition named CustomCondition that inherits from the

ActivityCondition class and overrides its Evaluate method, as shown in Listing 1 - 11 . My main goal in

this example is to show you that the full power of the SharePoint object model is at your disposal when

you ’ re developing a custom activity or condition.

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