Updating a string inside a callback

The following code is a graphic rendering of the Earth globe spinning eastward. I have two push buttons, Spin and Stop. Both share the same callback function, hAnimaCallback. In particular, this latter does not work. I pretend to use the strings (names) of the push buttons to create a switch that stops the movement. However, I can not get to change the string name inside the while loop and I do not understand why my method is wrong.

   function example
      fh = figure('Menu','none','Toolbar','none','Units','characters');
      T = 0:pi/100:2*pi;
      Y = zeros(numel(T),3);
      Y(:,1) = 7000*cos(T);
      Y(:,2) = 7000*sin(T);
      hPanAni = uipanel('parent',fh,'Units','characters','Position',...
          [22.6 10.4 53 23],'title','Controls','FontSize',11,...
          'FontAngle','italic','FontWeight','bold');
      hIniAni = uicontrol(hPanAni,'Style','pushbutton','Units','normalized',...
          'Position',[0.14 0.64 0.5 0.12],'String','Spin',...
          'FontSize',10,'Callback',@hAnimaCallback);
      hFinAni = uicontrol(hPanAni,'Style','pushbutton','Units','normalized',...
          'Position',[0.14 0.26 0.5 0.12],'String','Stop',...
          'FontSize',10,'Callback',@hAnimaCallback);
      hPantSim = uipanel('Parent',fh,'Units','characters',...
          'Position',[107.87 8 157.447 42],'BorderType','none','title',...
          'Screen','FontSize',11,'FontAngle','italic',...
          'FontWeight','bold');
      hPantSimInt = uipanel('Parent',hPantSim,'Units','normalized','Position',...
          [0 0 1 1],'BorderType','line','BackgroundColor','black');
      ah4 = axes('Parent',hPantSimInt,'Units','normalized','Position',...
          [0 0 1 1],'Color','none','Visible','off','DataAspectRatio',...
          [1 1 1],'NextPlot','add');
      rotate3d(ah4);
      hgrot = hgtransform('Parent',ah4);
      Resf = 6378;
      maptext = imread('tierra.jpg');
      [X, map] = rgb2ind(maptext,128);
      [x,y,z] = sphere(50);
      x = Resf*x;
      y = Resf*y;
      z = Resf*z;
      props.FaceColor= 'texture';
      props.EdgeColor = 'none';
      props.Parent = hgrot;
      props.Cdata = flipud(X); % it is necesary to do this for getting the 
      % appropiate image on the sphere
      hsurf = surface(x,y,z,props);
      colormap(map);
      axis equal;
      view([71 14]);
      set(gcf,'Renderer','opengl')
      drawnow;
      line('parent',ah4,'XData',Y(:,1),'YData',Y(:,2),'ZData',...
          Y(:,3),'Color','red','LineWidth',2);
      line('parent',ah4,'XData',Y(end,1),'YData',Y(end,2),...
          'ZData',Y(end,3),'Marker','o','MarkerSize',6,'MarkerFaceColor','b');
      axis square equal vis3d;
      view(3);
      handles.XLim = get(ah4,'XLim');
      handles.YLim = get(ah4,'YLim');
      handles.ZLim = get(ah4,'ZLim');
      xmin = handles.XLim(1);
      ymin = handles.YLim(1);
      zmin = handles.ZLim(1);
      xmax = handles.XLim(2);
      ymax = handles.YLim(2);
      zmax = handles.ZLim(2);
      set(ah4, 'XLim', [xmin xmax],'YLim', [ymin ymax],'Zlim',[zmin zmax]);
      az = 0;
          function hAnimaCallback(hObject,evt)
              while (ishandle(fh))
                  state = get(hObject,'String'), % state should change between the states of Spin and Stop but this does not occur
                  if (strcmp(state,'Stop'))
                      break;
                  else
                  az = az + 0.01745329252;
                  set(hgrot,'Matrix',makehgtform('zrotate',az));
                  drawnow;  
                  end  
              end
          end

      end

Answer 1

[Sean de Wolski]

Instead of using a while-loop I would highly recommend using a timer.

          function hAnimaCallback(hObject,evt)
              if isempty(timerfind) %spin
                  T = timer('tag','T','Period',0.001,'executionmode','fixedrate',...
                      'timerfcn',@make_her_spin);
                  start(T)
              else %stop
                  T = timerfind('tag','T');
                  stop(T);
                  delete(T)
              end    
          end
       function make_her_spin(hObject,evt)
            az = az + 0.01745329252;
            set(hgrot,'Matrix',makehgtform('zrotate',az));
            drawnow;  
       end

[Julián Francisco]

@Sean de Wolski: Thank you very much for your answer.

Answer 2

[Jan]

If you hit the 'Spin' button, the callback function is started:

function hAnimaCallback(hObject,evt)
while (ishandle(fh))
  state = get(hObject,'String')
  if (strcmp(state,'Stop'))
    break;
  else
    az = az + 0.01745329252;
    set(hgrot,'Matrix',makehgtform('zrotate',az));
    drawnow;  
  end  
end

This loops runs infinitely. When drawnow is reached, it allows to reacting to events.

If you now hit the 'Stop' button, the callback function is called again and the break statement is reached. The callback returns and the other instance of it is still running! The value of hObject is not changed by calling another instance of the callback.

You can use a persistent variable to share data between different instances of a function. Or you can store the status flag using setappdata in the figure.

[Julián Francisco]

@Jan Simon: Thank you so much for your explanation and suggestions.