From my understanding, you are trying to add a callback for ButtonDownFcnof the UIFigure to trigger the callback, when clicking on child axes. From the link that you have referenced, your requirement can be achieved by using WindowButtonDownFcn callback and not ButtonDownFcn. ButtonDownFcn callback is triggered when user clicks a blank area of the UI Figure
WindowButtonDownFcn callback executes when the user clicks:
- A blank area of the UI figure
- A UI component within the UI figure that supports the ButtonDownFcn property
- A graphics object within the UI figure that supports the ButtonDownFcn property
You can find WindowButtonDownFcn callback in the window section of UI Figure callbacks.
For more information on different callbacks, you can refer to Common callbacks, Keyboard Callbacks, Window Callbacks section here