The Invoker interface is used to define the possible interactions between the parent state machine (executor) and the types of invocable activities.
Invocable activities must first register an Invoker implementation class for the appropriate "targettype" (attribute of <invoke>) with the parent SCXMLExecutor
.
The communication link between the parent state machine executor and the invoked activity is a bi-directional events pipe.
All events triggered on the parent state machine get forwarded to the invoked activity. The processing semantics for these events depend upon the "targettype", and thereby vary per concrete implementation of this interface.
The invoked activity in turn must fire a special "done" event when it concludes. It may fire additional events before the "done" event. The semantics of any additional events depend upon the "targettype". The invoked activity must not fire any events after the "done" event. The name of the special "done" event must be the ID of the parent state wherein the corresponding <invoke> resides, with the String ".invoke.done" appended.
The Invoker "lifecycle" is outlined below:
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