Datasheet

Chapter 1: Workﬂ ow Programming Principles

It invokes the Initialize method on all activities in the new activity branch copy. This

basically does what a C# “ while ” loop does for each iteration. Recall that a C# “ while ” loop

resets all the local variables at the beginning of each iteration. In other words, no residual

effects are carried over from the previous iteration. The only difference is that C# resets the

same local variables, whereas WF creates a new copy of the child activity and its

descendants and calls the Initialize method on the new copy of the child activity and

its descendants.

It returns an ActivityExecutionContext object that represents the child execution context.

It accesses the new copy of the child activity of the WhileActivity activity and registers the

Activity_Closed event handler for the Closed event of this child activity copy:

childExecutionContext.Activity.Closed += Activity_Closed;

The child execution context exposes a property named Activity of the Activity type, which

returns a reference to the new copy of the child activity of the WhileActivity activity.

3. It invokes the ExecuteActivity method on the child execution context, passing in the reference to

the new copy of the child activity of the WhileActivity activity to schedule the Execute method

of the new copy of this child activity for execution:

childExecutionContext.ExecuteActivity(childExecutionContext.Activity);

Note that the Execute method of the WhileActivity activity uses the ExecuteActivity method of

the child execution context as opposed to the global execution context (keep in mind that the

global activity execution context is referenced through the ActivityExecutionContext object

passed into the Execute method of the WhileActivity activity) to schedule the Execute method

of the new copy of the child activity of the WhileActivity activity for execution. This ensures that

the new copy of the child activity is executed within the context of the child execution context as

opposed to the global execution context. This is similar to the C# while loop, where the content

of the while loop is executed in a local context as opposed to the global context:

return ActivityExecutionStatus.Executing;

At some point, the WF scheduler dispatches the work item that encapsulates the Execute method of the

new copy of the child activity of the WhileActivity activity and consequently invokes the Execute

method of the new copy of the child activity, passing in an activity execution context that represents the

new child execution context. This means that the Execute method of the new copy of the child activity

will be executed within the context of the new child execution context. This Execute method in turn may

have to suspend the execution of the new copy of the child activity waiting indefinitely for an external

input before it resumes its execution.

When the new copy of the child activity finally completes its execution and raises the Closed event, the

Activity_Closed event handler of the WhileActivity activity is scheduled for execution. At some point,

the WF scheduler finally invokes the Activity_Closed event handler, passing an

ActivityExecutionContext object that represents the global execution context because all execution

methods of the WhileActivity activity execute within the context of the global execution context. It is

only the execution methods of the new copy of the child activity of the WhileActivity activity that are

executed in the context of the new child execution context.

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