Creating Graphical User Interfaces

Output Function

The output function returns output arguments to the command line. This is particularly useful if you want to return a variable to another GUI. For an example, see Example: Using the Modal Dialog to Confirm an Operation.

GUIDE generates the following lines of code in the output function:

• % --- Outputs from this function are returned to the command line.
  function varargout = my_gui_OutputFcn(hObject, eventdata, 
  handles)
  % Get default command line output from handles structure
  varargout{1} = handles.output;
  

If the GUI is not blocking - in other words, if the M-file does not contain the command uiwait - the output is simply the handle to the GUI, which is assigned to handles.output in the opening function.

To make the GUI return a different output - for example, if you want it to return the result of a user response, such as pressing a push button - do the following:

• Add the command uiwait; to the opening function to make the M-file halt execution until a user activates a component in the GUI.
• For each component of the GUI where you expect a user response, make the callback update the value of handles.output, and execute uiresume.

For example, if the GUI contains a push button whose String property is 'Yes', add the following code to its callback to make the GUI return 'Yes' when the user presses the push button:

• handles.output = 'Yes';
  guidata(hObject, handles);
  uiresume;
  

See the section Managing GUI Data with the Handles Structure for more information about passing data with the handles structure.

When the GUI is called with the command

• OUT = my_gui
  

and a user presses the Yes push button, the GUI returns the output
OUT = 'Yes' to the command line.

The output varargout, which is a cell array, can contain any number of output arguments. By default, GUIDE creates just one output argument, handles.output. To create another output argument, add the command

• varargout{2} = handles.second_output;
  

to the output function. You can set the value of handles.second_output in any callback and then save it with the guidata command.

If you want, you can choose more descriptive names than output or second_output for the fields of the handles structure corresponding to the output arguments.

Opening Function

Callbacks