WF Activities

The following table provides short descriptions of the activities currently defined by WF.

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Activity Class	Purpose
CallExternalMethodActivity	Calls a routine in the external host program. Can push information from the workflow to the host program.
CancellationHandlerActivity	Holds cleanup logic for a composite activity that is canceled before completion.
CodeActivity	Executes Visual Basic or C# code in the workflow.
CompensatableSequenceActivity	A SequenceActivity that can be compensated (undone).
CompensatableTransactionScopeActivity	A TransactionScopeActivity that can be compensated (undone).
CompensateActivity	Causes compensation for an activity that supports it (implements the ICompensatableActivity interface).
CompensationHandlerActivity	Contains the activities that perform compensation for a composite activity.
ConditionedActivityGroup	Controls execution of a group of child activities. Depending on conditions for each child, the child activities are executed until a condition on the ConditionedActivityGroup is true. This lets you potentially execute multiple instances of the same activities in parallel.
DelayActivity	Adds a time delay to the workflow.
EventDrivenActivity	Executes activities in response to an event.
EventHandlersActivity	Associates events with activities to execute.
EventHandlingScopeActivity	Provides scope for EventHandlersActivity objects. Executes a main activity and simultaneously executes one or more EventHandlers?Activity objects if their events occur while the main activity is running.
FaultHandlerActivity	Handles specified types of exceptions.
FaultHandlersActivity	Contains a sequence of FaultHandlerActivity objects.
HandleExternalEventActivity	Responds to an external event raised by a host application. This object allows the host application to push information to the workflow code.
IfElseActivity	Tests a condition for each child activity and executes the first activity with a condition that is satisfied.
IfElseBranchActivity	Represents a branch for an IfElseActivity.
InvokeWebServiceActivity	Invokes a web service.
InvokeWorkflowActivity	Invokes another workflow.
ListenActivity	Waits until one of its EventDrivenActivity children receives its event, and then executes that child.
ParallelActivity	Executes two or more SequenceActivity objects at the same time.
PolicyActivity	Represents a collection of rules consisting of conditions and corresponding actions.
ReplicatorActivity	Creates copies of an activity.
SequenceActivity	Executes child activities sequentially.
SetStateActivity	Changes the state for a state machine workflow.
StateActivity	Represents a state for a state machine workflow.
StateFinalizationActivity	Contains activities to execute when a state machine workflow is leaving a state (sort of like a LeavingState event).
StateInitializationActivity	Contains activities to execute when a state machine workflow is entering a state (sort of like an EnteringState event).
SuspendActivity	Suspends the workflow, typically so you can handle some special error or condition.
SynchronizationScopeActivity	Executes activities sequentially in a synchronized domain so they have mutually exclusive access to shared variables.
TerminateActivity	Ends the workflow.
ThrowActivity	Throws an exception.
TransactionScopeActivity	Wraps a System.Transaction that you can roll back if it throws an exception.
WebServiceFaultActivity	Handles a web service fault.
WebServiceInputActivity	Publishes itself as a web service method and later executes when the method is called.
WebServiceOutputActivity	Provides output for a web service method request made to a WebServiceInputActivity.
WhileActivity	Repeatedly executes while a condition is satisfied.

Many of these classes must be used in particular combinations. For example, a WhileActivity can hold only a single child activity, so if you want to execute more than one activity in a loop, you need to put them inside some other grouping activity. For example, you could place them in a SequenceActivity and then put the SequenceActivity inside the WhileActivity.

For another example, the ListenActivity can contain only EventDrivenActivity children (and it must contain at least two). In a typical workflow, the EventDrivenActivity children might contain HandleExternalEventActivity children to take action.