Broken ButtonDownFcn when used in a class in R2015a

I have a class, 'scrollwindow', which uses the axis 'ButtonDownFcn' to get a mouse click and do stuff. My code worked fine until Version 8, but is now broken. The error report is:

Undefined function 'down' for input arguments of type 'matlab.graphics.axis.Axes'.

Here's the relevant code, reduced to its essentials:

    methods
        function s = scrollwindow(varargin)
      ...
            set(gca, 'ButtonDownFcn', @(src, evt)down(src, evt, s));
      ...
        end

    methods (Access = private)
        function down(src, evt, s)
      ...
        end
    end
end

Any suggestions would be appreciated.

Answer 1

[Etaoin Shrdlu]

"Nevah mind!" I figured it out:

methods
  function s = scrollwindow(varargin)
      ...
      set(gca, 'ButtonDownFcn', @(src, evt)down(s));
      ...
  end
end
  
methods (Access = private)
  function down(s)
  ...
  end
end

Answer 2

[Steven Lord]

The reason this used to work is because prior to the introduction of the new graphics system in release R2014b, axes handles were double precision values and user-defined objects take priority over fundamental classes when determining which function or method is called.

With release R2014b, axes handles are now handle objects. Since the src input argument to the ButtonDownFcn is an axes and is left/before the instance of your scrollwindow class, MATLAB will look for a method named down of the axes class. It can't find it, so you receive this error.

Removing the axes handle from your down call is one way to resolve the problem. Changing the relative precedence of the axes class and your scrollwindow class is another.

[Etaoin Shrdlu]

Thanks, Steve. This makes total sense.

Etaoin S.