Question

I created a class which adds functionality to a figure on construction. This class creates a listener for the WindowMouseMotion event; however, to get this event to fire I had to add a dummy callback function for the figure’s WindowButtonMotionFcn property. I first check if this property is already populated. If it isn’t then I set it to a dummy callback function that does nothing.

Instead of checking if the property is already set or not, can I simply add this dummy callback to any existing callbacks? Is it possible for a callback property to call multiple functions?

EDIT

When using the handle.listener approach to handle the WindowButtonMotionEvent event given below, be sure to use eventdata.CurrentPoint to access the current mouse position. The CurrentPoint property of the figure does not get updated before handling the WindowButtonMotionEvent event in this manner.

Answer 1

A related article can be found on Yair Altman’s Undocumented MATLAB blog, from guest blogger Matt Whitaker. What you are alluding to is callback chaining, and quoting from the blog:

Frankly, having written code
previously that handles callback
chaining, I would rather poke myself
in the eye with a fork!

Luckily, there appears to be an alternative solution in that article. Using a snippet from the code posted there, I was able to get a function to execute on mouse movement without having to set the 'WindowButtonMotionFcn'. I added a listener to the current figure like so:

myListener = handle.listener(gcf,'WindowButtonMotionEvent',...
                             @(hSource,eventData) disp('hello'));

And the message hello was displayed when I moved the mouse in the window.