MATLAB SIMULINK 7 - GRAPHICAL USER INTERFACE Manuel d'utilisateur télécharger pdf (Page 174)

8 Programming the GUI

8-2

Callbacks: An Overview

After you have laid out your GUI, you need to program its behavior. The code

you write controls how the GUI responds to events such as button clicks, slider

movement, menu item selection, or the creation and deletion of components.

This programming takes the form of a set of functions, called callbacks, for each

component and for the GUI figure itself.

This chapter addresses the programming of GUIs created using GUIDE. In

particular, this section explains:

• “What Is a Callback?” on page 8-2

• “Kinds of Callbacks” on page 8-2

What Is a Callback?

A callback is a function that you write and associate with a specific GUI

component or with the GUI figure. It controls GUI or component behavior by

performing some action in response to an event for its component. This kind of

programming is often called event-driven programming.

When an event occurs for a component, MATLAB invokes the component’s

callback that is triggered by that event. As an example, suppose a GUI has a

button that triggers the plotting of some data. When the user clicks the button,

MATLAB calls the callback you associated with clicking that button, and the

callback, which you have programmed, then gets the data and plots it.

A component can be any control device such as a push button, list box, or slider.

It can also be a menu or a container such as a panel or button group. See

“Available Components” on page 6-14 for a list and descriptions of components.

Kinds of Callbacks

The GUI figure and each type of component has specific kinds of callbacks with

which it can be associated. The callbacks that are available for each component

are defined as properties of that component. For example, a push button has

five callback properties:

ButtonDownFcn, Callback, CreateFcn, DeleteFcn, and

KeyPressFcn. A panel has four callback properties: ButtonDownFcn, CreateFcn,

DeleteFcn, and ResizeFcn. You can, but are not required to, create a callback

function for each of these properties. The GUI itself, which is a figure, also has

certain kinds of callbacks with which it can be associated.

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MATLAB SIMULINK 7 - GRAPHICAL USER INTERFACE Manuel d'utilisateur Page 174