handler_group.md
In rswipl: Embed 'SWI'-'Prolog'

class handler_group {#class-handler_group}

A handler_group object is a collection of recogniser objects (hence, a better name would be recogniser_group; this might change). It provides a means to combine a set of recognisers, each dealing with some detailed UI behaviour into one object dealing with many UI behaviours. Handler groups may be nested. This process may be repeated to get more complex event-recognisers.

It is common practice to combine recognisers. Suppose the user interface contains a (large) number of icons that should be movable and double-click should open the icon.. In this case a recogniser would be declared as:

:- pce_global(@icon_recogniser, new(handler_group(
        new(move_gesture),
        new(click_gesture(left, '', double,
                          message(@receiver, open)))))).

Bugs: Should be called recogniser_group

@see object->recogniser

handler_group->delete: recogniser Delete first occurrence of recogniser
handler_group->event: event Process an event object. Simply invokes ->event on each of the <-members until this message succeeds. If no recogniser accepts the event it fails.

handler_group<-_arg: int -> recogniser Return the nth element of <-members. See object <-_arg.
handler_group<-_arity: -> int Number of elements in <-members. See object <-_arity.