Changing class properties with callback function

Hi,

I want to create a control that is handling my figures. I will put down a minimal example here. My main problem is how to change a class property (m_CurFigureIndex), when executing a callback function.

So the main routine is:

close all;

figure('name','F1')
figure('name','F2')
figure('name','F3')

FC = C_MinFigureControl;
FC = FC.ActivateEventControls;

And my class definition:

classdef C_MinFigureControl

      properties
          m_FigureHandle
          m_CurFigureIndex
      end

      methods (Access = public)

          function obj = C_MinFigureControl

              obj.m_CurFigureIndex = 1;
              obj = obj.GetAllFigH;
              figure(obj.m_FigureHandle(obj.m_CurFigureIndex))

          end % function C_MinFigureControl

          function obj = GetAllFigH(obj)

              obj.m_FigureHandle = findobj('Type','figure');

              if ~isempty(obj.m_FigureHandle)
                  [~, ind] = sort([obj.m_FigureHandle.Number]);
                  obj.m_FigureHandle = obj.m_FigureHandle(ind);
              end % if not empty

          end % function GetAllFigH

          function obj = Scroll(obj, ScrollCount)

              obj.m_CurFigureIndex = obj.m_CurFigureIndex + ScrollCount;

              obj.m_CurFigureIndex = max(obj.m_CurFigureIndex,1);
              obj.m_CurFigureIndex = min(obj.m_CurFigureIndex,length(obj.m_FigureHandle));

              figure(obj.m_FigureHandle(obj.m_CurFigureIndex))

          end % function Scroll

          function obj = ActivateEventControls(obj)

              set(obj.m_FigureHandle,'WindowScrollWheelFcn',@obj.FigScroll);

          end % function ActivateEventControls

          function FigScroll(obj,src,CallBackData)

              ScrollCount = 0;

              if strcmp(CallBackData.EventName,'WindowScrollWheel')
                  ScrollCount = CallBackData.VerticalScrollCount;
              end % if CallBackData

              obj = obj.Scroll(ScrollCount);

          end

      end

end

So I am getting all figure handles and then create a callback function for scrolling with the mousewheel (FigScroll). I wanna change m_CurFigureIndex on each scroll to keep track of the current figure. This one does not work, I do not know how to pass back the value, so that the real class does change. Appears there is always just the copy changing. So next scroll event I am always back to m_CurFigureIndex = 1.

I would appreciate any hint for a fix or a hint what a more proper way of coding this is.

Thank you in advance Sven

Answer 1

[Adam]

Derive your class from handle is the easiest way:

classdef C_MinFigureControl < handle

This brings in a few differences from a by-value class, one of which being that the object as by-reference copy semantics.

Note that if you do that you don't need to return obj out of your functions and reassign the object. It doesn't do any harm, but is redundant for a handle-derived class.

http://uk.mathworks.com/help/matlab/matlab_oop/comparing-handle-and-value-classes.html

[Sven]

Thanks alot, that was exactly what I am looking for. Just changing the line as you indicated did the job. Thought it must be something small.