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SCO Visual Tcl terminology and concepts

Events and callbacks

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

Graphical, event-driven programming is different from traditional programming in that the program does not dictate the flow of control. Instead, the user, by their choice of actions, generates events which the program may or may not respond to.

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''.


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