Callbacks in Programmatically Created GUIs :: Working with Callbacks (Draft) (Creating Graphical User Interfaces)

Creating Graphical User Interfaces

Callbacks in Programmatically Created GUIs

Although you may eventually want to define your own syntactical conventions, the following provides a good place to start.

Function Definition

Your function definition could look something like this:

% Description of event that triggers callback execution.
function pushbutton1_Callback(source, eventdata, handles,...) 
...

The comment line describes the event that triggers execution of the callback.

To help you remember the component and callback property with which this callback is associated, construct the callback name by appending an underscore (_) and the name of the callback property to the component's Tag property. In the example above, pushbutton1 is the Tag property for the push button, and Callback is one of the push button's callback properties. See Associating Callbacks with Components for more information.

Input Arguments

If you use a handle to specify the callback in the component callback property, i.e., @pushbutton_callback as shown here

set(h,'Callback',{@pushbutton_callback,handles,...})

MATLAB automatically passes the handle of the component for which the event was triggered and eventdata as the first two arguments of the callback. The function definition line for your callback must account for these two arguments. The second element of the cell array, handles in the example above, becomes the third argument of the callback. For example,

function pushbutton1_callback(source,eventdata,handles,...)

The input arguments are defined as:

source -- Handle of the object for which the callback was triggered.
eventdata -- Reserved for later use.

Note Three eventdata fields are defined for use with button groups. These fields enable you to determine the previous and current radio or toggle button selections maintained by the buttoon group. See SelectionChangeFcn in the Uibuttongroup Properties for more information.

handles -- Structure you create with the guihandles function, prior to setting the component callback properties, that contains the handles of all the objects in the figure. It may also contain application-defined data.

Note If you are using nested functions, you do not need this argument to access the component handles. See Files for Programmatically Created GUIs for more information.

For a GUI that contains an edit text, a uipanel, a popup menu, and a push button, the handles structure you create with guihandles looks similar to this. guihandles uses the component Tag properties to name the elements of the structure.
- ```
handles = 
        figure1: 160.0011
          edit1: 9.0020
       uipanel1: 8.0017
     popupmenu1: 7.0018
    pushbutton1: 161.0011
         output: 160.0011
```

If you make any changes to this structure, you must explicitly save it before exiting the callback. To do this, you can use either guidata or setappdata. See Managing Application-Defined Data for information about using these functions.

Callback Conventions in GUIDE Initialization Callbacks in GUIDE