GUIDATA does not trasfer data in GUIDE with subfunctions.

I have a simple GUIDE with 2 pushbuttons. Button #1 plots a sine graph and button #2 adds a "draggable" vertical line to the graph. Idea is based on the link bellow [1]

I'm using guidata to transfer data between subfunctions and callbacks in the `GUIDE`. But one of the shared variables (mousedown) does not transmit between the callbacks. What causes the loss of data transfer between the subfunctions in GUIDE?

Here are the callbacks with their subfunctions (the entire code is attached):

          % ######### Callbacl 1: Graph SIN function  
          function pushbutton_plot_Callback(hObject, eventdata, handles)   
          clc;
          open_figs_h = get(0,'children');
          close(open_figs_h(2:end));

          x = -pi:0.01:pi;
          y = sin(x);

          fig_h = figure('units','normalized','outerposition',[0.2 0.2 .5 .5],'WindowButtonMotionFcn', @MouseMove, 'WindowButtonUpFcn', @MouseUp );
          axis_h = axes('parent',fig_h,'position',[0.1 0.1 .8 .8]);
          line('parent',axis_h,'xdata',x,'ydata',y);

          handles.axis_h = axis_h;
          guidata(hObject,handles);

              % MouseUp and MouseMove subfunctions in callback 1
              function MouseUp(h,event) %#ok<*INUSD>
                  mousedown = false;
              end
              function MouseMove(h,event)
                  if isfield(handles,mousedown)
                      mousedown = handles.mousedown;
                  else
                      mousedown = false;
                  end

                  if mousedown
                      cp = get ( axis_h, 'CurrentPoint' );
                      vertline_h = handles.vertline_h;
                      set ( vertline_h, 'XData', [cp(1,1) cp(1,1)] );
                  end
              end
          end

          %######### Callbacl 2: Graph movables vertical line      
          function pushbutton_vertline_Callback(h, eventdata,handles)
          axis_h = handles.axis_h;
          vertline_h = line('parent',axis_h,'xdata',[1 1],'ydata',[-1 1], 'ButtonDownFcn', @mouseDown );

          handles.vertline_h = vertline_h;
          guidata(h,handles)

              % MouseMove subfunction in callback 2
              function mouseDown(hObject,event)
                  mousedown = true;
                  handles.mousedown = mousedown;
                  guidata(hObject,handles)
              end
          end

[1]: http://stackoverflow.com/questions/26365960/re-generating-a-draggable-line-in-matlab-gui

Answer 1

[Geoff Hayes]

Alborz - your code has interesting approach by assigning the ButtonDownFcn to the line object so that when the user presses down on the line (and only the line), this event will fire. Though instead of calling guidata with hObject which is the handle to the line object, you probably want to call it with the handle to the button, h, since it is a child of the GUI and the handles structure is "associated" with that. So the pushbutton_vertline_Callback code would change to

 function pushbutton_vertline_Callback_Callback(hButton, eventdata,handles)
    axis_h = handles.axis_h;
    vertline_h = line('parent',axis_h,'xdata',[1 1],'ydata',[-1 1], 'ButtonDownFcn', @mouseDown );
    handles.vertline_h = vertline_h;
    guidata(h,handles)
    % MouseMove subfunction in callback 2
    function mouseDown(hObject,event)
        mousedown = true;
        handles.mousedown = mousedown;
        guidata(hButton,handles)
    end
 end

Like Walter has indicated, your mousedown variable is local to the MouseUp function and so setting it to true won't affect the field within the handles structure. So this function should change to

 function MouseUp(h,event) %#ok<*INUSD>
    handles = guidata(hObject);
    handles.mousedown = false;
    guidata(hObject,handles);
 end

Note how in the above code, we use hObject (the handle to the pushbutton_plot) to get the latest updated version of handles rather than the older copy from the pushbutton_plot_Callback callback. So we get the latest version, change the mousedown field, and then save the updated handles structure.

And the MouseMove is almost correct with the only problem being that the handles of copy being used rather than the latest version. Again, we just need to call guidata as

 function MouseMove(h,event)
     handles = guidata(hObject);
     if isfield(handles,'mousedown')
         mousedown = handles.mousedown;
     else
         mousedown = false;
     end
     if mousedown
         cp = get ( axis_h, 'CurrentPoint' );
         vertline_h = handles.vertline_h;
         set ( vertline_h, 'XData', [cp(1,1) cp(1,1)] );
     end
 end

See below for the full code which should work.

 % Callbacl 1: Graph SIN function 
 function pushbutton_plot_Callback(hObject, eventdata, handles)   
    clc;
    open_figs_h = get(0,'children');
    close(open_figs_h(2:end));
    x = -pi:0.01:pi;
    y = sin(x);
    fig_h = figure('units','normalized','outerposition',[0.2 0.2 .5 .5],...
                   'WindowButtonMotionFcn', @MouseMove, 'WindowButtonUpFcn', @MouseUp );
    axis_h = axes('parent',fig_h,'position',[0.1 0.1 .8 .8]);
    line('parent',axis_h,'xdata',x,'ydata',y);
    handles.axis_h = axis_h;
    guidata(hObject,handles);
    % MouseUp and MouseMove subfunctions in callback 1
    function MouseUp(h,event) %#ok<*INUSD>
        handles = guidata(hObject);
        handles.mousedown = false;
        guidata(hObject,handles);
    end
    function MouseMove(h,event)
        handles = guidata(hObject);
        if isfield(handles,'mousedown')
            mousedown = handles.mousedown;
        else
            mousedown = false;
        end
        if mousedown
            cp = get ( axis_h, 'CurrentPoint' );
            vertline_h = handles.vertline_h;
            set ( vertline_h, 'XData', [cp(1,1) cp(1,1)] );
        end
    end
 end 

 % Callbacl 2: Graph movables vertical line      
 function pushbutton_vertline_Callback(hButton, eventdata,handles)
    axis_h = handles.axis_h;
    vertline_h = line('parent',axis_h,'xdata',[1 1],'ydata',[-1 1], 'ButtonDownFcn', @mouseDown );
    handles.vertline_h = vertline_h;
    guidata(h,handles)
    % MouseMove subfunction in callback 2
    function mouseDown(hObject,event)
        mousedown = true;
        handles.mousedown = mousedown;
        guidata(hButton,handles)
    end
  end

[Alborz Sakhaei]

Thank you very much Geoff. Appreciate your time. That completely resolved my issue. Just one minor comment: In pushbutton_vertline_Callback the line guidata(h,handles) should be guidata(hButton,handles). Please correct me if I'm mistaken. Thanks again, Alborz

[Geoff Hayes]

For sure, Alborz. Yes, you are correct - the line should read

 guidata(hButton,handles)

Answer 2

[Walter Roberson]

In order for a variable to be shared it must be initialized in the containing routine before the declaration of the subfunctions that share it. It then becomes shared only with the containing and contained routines.

You are not using the mousedown variable in a shared way. Even if you had initialized it before the subfunctions, in the second subfunction you test whether handles has a field with that name and if so then you grab that value and if not then you force the variable to false. Any shared value would be overwritten. No other routines read the shared value so that is not for the benefit of some other routine.

Consider too that you do not delete out of handles when you poll in the nested function so the next time through you would pull from the handles again. You have no code that sets the handles version to false or removes it, so once set the handles version is going to remain true.

[Alborz Sakhaei]

Thank you Walter for your insight. Always helpful.