Creating Graphical User Interfaces

Changing Component Tag Properties

Guide automatically assigns a string to the uicontrol Tag property and uses this string to:

• Construct the name of the generated callback subfunctions (e.g., tag_Callback)
• Add a field to the handles structure containing the handle of the object (e.g., handles.tag).

If you change the Tag after GUIDE generates the callback subfunction, GUIDE does not generate a new subfunction. However, since the handles structure is created at run-time, GUIDE uses the new Tag to name the field that contains the objects handle.

Problems Caused by Changing Tags

Changing the Tag can cause program errors when you have referenced an objects handle. For example, the following statement,

file_list = get(handles.listbox1,'String');

gets the value of the String property from the list box whose Tag is listbox1. If you had changed the list box's Tag to file_listbox, subsequent instantiations of the GUI would require you to change the statement to:

file_list = get(handles.file_listbox,'String');

Avoiding Problems

The best approach is to set the Tag property on components when you add them to the layout. If you do change a Tag after generating the application M-file and want to rename callback subfunctions to maintain the consistent naming used by GUIDE, you should:

• Correct any out of date reference to the handles structure.
• See Changing the Name of Callback Subfunctions and follow the procedure described there.

Renaming Application Files and Tags

Changing the Name of Callback Subfunctions