Events and callbacks

``Events'' are simply ways the user manipulates widgets, such as:

• pushing a button

• selecting a list item

• choosing a menu item

Responses to events are called ``callbacks'', and each callback has an associated procedure. This procedure is called each time the associated event occurs. For example, if you wrote a callback for a pushButton widget, it would be called each time the button was pressed. This graphic illustrates several other callback routines:

When you issue a callback, data is returned using ``keyed lists''. These key/value pairs (such as the name of a label of a button) can be manipulated using the keyed list commands, keyldel(1tcl), keylget(1tcl), keylkeys(1tcl), and keylset(1tcl).

For examples of using callbacks and procedures, see ``Defining the callbacks''.

For more information on using callbacks and procedures, see ``Using callbacks and procedures''.