1.72 class handler

A handler object is a reusable object that defines how a graphical object should respond when it is sent an event object. A handler maps an event<-id onto an action realised .by a code object.

By default, handlers traps events anywhere on an object. Using the handler<-region, the handler can be active for a subregion of the object.

Bugs:

Handlers only handle single events and have no elegant way to represent status information. The are retained for backward compatibility reasons. New code should first look at the class gesture or class key_binding.

See also

- @event_tree
- class gesture
- class region
- topic Event types
- class popup
- object->recogniser

1.72.1 Instance variables

handler <- event: event_id

event<-id of the events this handler is sensitive to. When an event arrives, it is tested using event->is_a, given the value of this variable.

handler <-> message: code*

Code executed when the handler fires. Arguments:

@receiver	event<-master (normally event<-receiver).
@arg1	The event.

handler <-> region: [region]

Region of graphical the event must be in. See class region for details. Used infrequently.

1.72.2 Send methods

handler ->event: event

Request to process an event. This method is normally invoked from graphical->event. It will forward handler<-message iff event->is_a succeeds for the argument event using handler<-event and if no handler<-region is specified or the argument event is inside the handler<-region.

handler ->initialise: event=event_id, message=code*, restrict_to=[region]

Create a handler from the event_id mapped, the code it is mapped on and optionally a region to which its activation is limited. For semantics, see handler->event.