All specified handlers could be registered or deregistered.
At least one of the specified handlers could not be registered, as it is already registered for the same event.
At least one of the specified handlers could not be deregistered, as it is not registered for the event in question.
The statement SET HANDLER manages internally different system tables that
associate the event raisers and event handlers with each in single registrations, mass registrations,
and registrations of static events. Each registration represents a row in one of the system tables assigned
to the event raiser. A handler can only appear once in a particular system table, but can appear in
multiple system tables, that is, it can be registered for different events. When the system raises an
event using RAISE EVENT, it evaluates the corresponding system tables and calls the event handlers registered there.
The order of the calls of registered event handlers is not defined and can change during program runtime. To get a fixed order of different method calls, these can be called in one event handler.
When registering an instance method, a reference to the corresponding object in the relevant table is created and then deleted again when deregistering. With respect to the
such a reference has the same effect as a reference in a reference variable. Objects registered as handlers
are not deleted as long as they are registered, that is, they are not deregistered using the ACTIVATION
addition. If a raising instance is deleted by the garbage collector, the corresponding system table is also deleted and as a result, its registrations are reversed.
If the statement SET HANDLER registers the current handler again for the
current event in event handling, it is not clear whether the registration is ignored by the current event handler. This can produce endless recursions and should be avoided.
Registration of event handlers for two instance events and a static event. In the first statement
SET HANDLER, a static event handler h1 and an instance method
h2, are registered for the instance events e1 and e2
of the object referenced by the reference variable trigger. In the second
statement SET HANDLER, an instance method h3 is registered for the static event ce1 of the class c1.
CLASS c1 DEFINITION. PUBLIC SECTION. EVENTS e1.
CLASS-EVENTS ce1. ENDCLASS.
CLASS c2 DEFINITION INHERITING FROM c1.
PUBLIC SECTION. EVENTS e2. ENDCLASS.
CLASS c3 DEFINITION.
PUBLIC SECTION. CLASS-METHODS h1 FOR EVENT e1 OF c1.
METHODS: h2 FOR EVENT e2 OF c2,
h3 FOR EVENT ce1 OF c1.
DATA: trigger TYPE REF TO c2, handler TYPE REF TO c3.
SET HANDLER: c3=>h1 handler->h2 FOR trigger, handler->h3.