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ABL Reference
ABL Syntax Reference : UNSUBSCRIBE statement
 

UNSUBSCRIBE statement

Cancels a subscription to an ABL named event. Specifically, the UNSUBSCRIBE statement cancels one or more subscriptions to one or more named events.
Note: ABL named events are completely different from the key function, mouse, widget, and direct manipulation events, which are described in the Handle-based Object Events Reference. They are also different from the class events described in the Class Events Reference.

Syntax

UNSUBSCRIBE [ PROCEDURE subscriber-handle ]
[ TO ] { event-name | ALL } [ IN publisher-handle ]
PROCEDURE subscriber-handle
A procedure handle representing the subscriber to a named event.
The PROCEDURE option lets one procedure cancel a subscription on behalf of another. For example, if you want procedure A to cancel a subscription on behalf of procedure B, set subscriber-handle to the procedure handle of B.
If the PROCEDURE option does not appear, the AVM assumes that the subscriber is THIS-PROCEDURE, the procedure that contains the UNSUBSCRIBE statement.
event-name
A quoted string or character expression representing the name of a named event.
ALL
Cancels all subscriptions.
IN publisher-handle
A procedure handle representing the publisher of a named event.
If the IN option appears, the AVM cancels subscriptions to named events published by publisher-handle-specifically, either all subscriptions (if the ALL option appears), or only subscriptions to event-name (if event-name appears).
If the IN option does not appear, the AVM cancels subscriptions regardless of the publisher-specifically, either all subscriptions (if the ALL option appears), or only subscriptions to event-name (if event-name appears).

Example

For an example, see the reference entry for the PUBLISH statement.

Notes

*When the AVM executes an UNSUBSCRIBE statement, it cancels a subscription when it finds a match. A match means that the SUBSCRIBE and UNSUBSCRIBE event names match, and that one of the following is true:
*The subscription was created using SUBSCRIBE IN, cancelled using UNSUBSCRIBE IN, and the publisher and subscriber handles in the SUBSCRIBE and UNSUBSCRIBE statements match.
*The subscription was created using SUBSCRIBE ANYWHERE, and cancelled using UNSUBSCRIBE without the IN option.
*The AVM executes the UNSUBSCRIBE statement with an implicit NO-ERROR option. That is, if the AVM cannot find a match, it does not report an error. To find out what errors, if any, occurred, use the ERROR-STATUS system handle.
*If you create a subscription using SUBSCRIBE ANYWHERE, you cannot cancel the subscription using UNSUBSCRIBE IN.

See also

PUBLISH statement, PUBLISHED-EVENTS attribute, SUBSCRIBE statement, Unsubscribe( ) event method