bindtags - Determine which bindings apply to a window, and order of evaluation




When a binding is created with the bind command, it is associated either with a particular window such as $widget, a class name such as Tk::Button, the keyword all, or any other string. All of these forms are called binding tags. Each window contains a list of binding tags that determine how events are processed for the window. When an event occurs in a window, it is applied to each of the window's tags in order: for each tag, the most specific binding that matches the given tag and event is executed. See the bind manual entry for more information on the matching process.

By default, each window has four binding tags consisting of the name of the window, the window's class name, the name of the window's nearest toplevel ancestor, and all, in that order. Toplevel windows have only three tags by default, since the toplevel name is the same as that of the window. The bindtags command allows the binding tags for a window to be read and modified.

If $widget->bindtags is invoked without an additional argument, then the current set of binding tags for $widget is returned as a list. If the tagList argument is specified to bindtags, then it must be a proper list; the tags for $widget are changed to the elements of the list. The elements of tagList may be arbitrary strings or widget objects, if no window by exists for an object at the time an event is processed, then the tag is ignored for that event. The order of the elements in tagList determines the order in which binding scripts are executed in response to events. For example, the command


reverses the order in which binding scripts will be evaluated for a button named $b so that all bindings are invoked first, following by bindings for $b's toplevel, followed by class bindings, followed by bindings for $b.

The bindtags command may be used to introduce arbitrary additional binding tags for a window, or to remove standard tags. For example, the command


replaces the (say) Tk::Button tag for $b with TrickyButton. This means that the default widget bindings for buttons, which are associated with the Tk::Button tag, will no longer apply to $b, but any bindings associated with TrickyButton (perhaps some new button behavior) will apply.


The current mapping of the 'native' Tk behaviour of this method - returning a true list but only accepting a reference to a list is counter intuitive. The perl/Tk interface may be tidied up.




binding, event, tag