Chapter 26. Binding Commands to Events

This chapter introduces the event binding mechanism in Tk. Bindings associate a Tcl command with an event like a mouse click or a key stroke. There are also facilities to define virtual events like <<Cut>> and <<Paste>> that are associated with different keystrokes on different platforms. Tcl commands discussed are: bind, bindtags, and event.

Bindings associate a Tcl command with a sequence of events from the window system. Events include key press, key release, button press, button release, mouse entering a window, mouse leaving, window changing size, window open, window close, focus in, focus out, and widget destroyed. The bindings are defined on binding tags, and each widget is associated with an ordered set of binding tags. The binding tags provide a level of indirection between bindings and widgets that creates a flexible and powerful system.

Virtual events are used to support a different look and feel on different platforms. A virtual event is a higher-level name, like <<Copy>>, for a lower-level event name like <Control-c> or <Key-F6>. A virtual event hides the different keystrokes used on different platforms for the same logical operation. Tk defines a few virtual events, and applications can define their own.