Generate Callback Function Prototypes :: Laying Out GUIs and Setting Properties (Creating Graphical User Interfaces)

Creating Graphical User Interfaces

Generate Callback Function Prototypes

When you select Generate callback function prototypes in the GUI Options dialog, GUIDE adds the most commonly used subfunctions to the GUI M-file for any component you add to the GUI. You must then write the code for the callback in this subfunction.

GUIDE also adds a subfunction whenever you edit a callback routine from the Layout Editor's right-click context menu and when you add menus to the GUI using the Menu Editor.

Naming Callback Subfunctions

When you add a component to your GUI layout, GUIDE assigns a value to its Tag property, which is then used to generate the name of the callback.

For example, the first push button you add to the layout is tagged pushbutton1. When generating the M-file, GUIDE adds a callback subfunction called pushbutton1_Callback. If you define a ButtonDownFcn for the same push button, GUIDE names its subfunction pushbutton1_ButtonDownFcn.

Callback Function Syntax

The callback function syntax is of the form

function objectTag_Callback(hObject, eventdata, handles)

The arguments are listed in the following table.

Argument
Description

hObject
The handle of the object whose callback is executing.

eventdata
Empty -- reserved for future use.

handles
A structure containing the handles of all components in the GUI whose fieldnames are defined by the object's Tag property. Can also be used to pass data to other callback functions or the command line.

Argument	Description
`hObject`	The handle of the object whose callback is executing.
`eventdata`	Empty -- reserved for future use.
`handles`	A structure containing the handles of all components in the GUI whose fieldnames are defined by the object's `Tag` property. Can also be used to pass data to other callback functions or the command line.

For example, if you create a layout having a push button whose Tag property is set to pushbutton1, then GUIDE generates the following subfunction header in the GUI M-file.

function pushbutton1_Callback(hObject, eventdata, handles)

Assigning a Callback Property String

When you first add a component to your GUI layout, its Callback property is set to the string %automatic. This string signals GUIDE to replace it with one that calls the appropriate callback subfunction in the GUI M-file when you save or run the GUI. For example, GUIDE sets the Callback property for pushbutton1 uicontrol to

my_gui('pushbutton1_Callback',gcbo,[],guidata(gcbo))

where

my_gui is the name of the GUI M-file.
pushbutton1 is the value of the component's Tag property.
pushbutton1_Callback is the name of the callback routine subfunction defined in my_gui.
gcbo is a command that returns the handle of the callback object (i.e., pushbutton1).
[] is a place holder for the currently unused eventdata argument.
guidata(gcbo) returns the handles structure.

See Callback Function Syntax for more information on callback function arguments and Changing Tag and Callback Properties for more information on how to change the names used by GUIDE.

Adding Callbacks to the M-file

If you want GUIDE to include other callbacks in the GUI M-file and provide names for them, you can do one of the following:

In the Property Inspector, set the value of the callback property, e.g., KeyPressFcn, to the string %automatic. GUIDE adds the callback to the M-file the next time you save the GUI.
In the View menu, select View Callbacks. Then select the desired callback, e.g., KeyPressFcn. GUIDE adds the callback to the M-file, opens the M-file if it is not already open, and scrolls to the first line of the new callback.

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