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Object-oriented Programming
Programming with Class-based and Procedure Objects : Using handle-based object events in classes

Using handle-based object events in classes

ABL supports events with several different constructs. Classes support widget and low-level ABL events using the ON statement, and they support ProDataSet, query, and buffer object callbacks using the SET-CALLBACK( ) method. Classes also allow you to publish named events associated with external procedures using the PUBLISH statement’s FROM publisher-handle option and they allow you to manage subscriptions of internal procedures as event handlers for named events using the SUBSCRIBE and UNSUBSCRIBE statements’ PROCEDURE subscriber-handle option. However, you cannot subscribe class methods to named events as event handlers or otherwise provide behavior to a class using named events. Classes support class events as members that provide a similar form of event behavior for a class. For more information, see Defining events within a class.
* ON statement
* SET-CALLBACK( ) method