MATLAB: error using drawnow: Interrupt while evaluating uicontrol Callback

Hi, I have a problem with a while loop inside a switch-case statement, used together with callback functions and "drawnow". In my code, while the cases of the switch-case are determined by pushbuttons in uicontrol, the case statements involves further callback functions to track mouse movements using 'windowbuttondown/up/motionfcn's. Because I draw multiple plots inside the while loop in the case statement, however, I use 'drawnow', which gives me the following error when I run the programme:

Error on line 160 ==> drawnow ??? Interrupt while evaluating uicontrol Callback

The piece of code inside the case statement gives no error when I run independently but somehow creates problem when is integrated with the rest of the code, which I attach below. Any help would be so much appreciated. Many thanks!

function programme(selection)

if nargin == 0 
selection=0
end

switch selection
case 0 %start GUI and uicontrols to set up the cases i.e %programme(1), programme(2) etc         
  uicontrol('style','pushbutton',...
      'string','First', ...
      'position',[50 700 50 20], ...
      'callback','programme(1);');
  uicontrol('style','pushbutton',...
      'string','Second', ...
      'position',[150 700 50 20], ...
      'callback','programme(2);');

    case 1

    %mouse track:
    set(gcf,'windowbuttondownfcn','mousedown=1;');
    set(gcf,'windowbuttonupfcn','mouseup=1;');
    set(gcf,'windowbuttonmotionfcn','mousemotion=1;');

    %to terminate the while loop, set up stopit=1 on one of uicontrol buttons:   
    uicontrol('style','pushbutton',...
        'string','First', ...
        'position',[50 700 50 20], ...
        'callback','stopit=1;');

    stopit=0;

    while (stopit==0)
        if mousedown==1
            statements   
            if mouseup ==1
                statements (plots)
                mouseup=0;
                mousedown=0;
                mousedown=0;
            end
        end
        drawnow
    end

    case 2
    statements
    otherwise
    statements
    end

Answer 1

[Sean de Wolski]

The moral of the story is: Don't use a while loop for this!

When the mouse is pushed the windowbuttondownfcn callback is fired. Inside this, change the windowbuttonmotionfcn to be your set of statements to execute while the button is down. Then when the windowbuttonupfcn is fired (i.e. release the mouse) reset the windowbuttonmotionfcn and fire the statements that you want for when they let up.

The solutions here may interest you:

http://blogs.mathworks.com/videos/2011/03/29/graphics-challenge-for-new-users/

Answer 2

[Jan]

Because I cannot reproduce the error, I cannot guess its reason. Could you please post a program, which is working?

But I see another problem: What do you expect the callback "stopit=1;" to do? It modifies the variable "stopit" in the base-workspace, such that you can check it in the command window. But this does not matter the variable "stopit" inside your function "programme". I suggest to read Matt's GUI examples to learn how to use callbacks: FEX: 41 GUI examples.

[inci]

The problem seems to be with the while loop used together with drawnow and callback functions but I cannot think of another way of doing what I am trying to do.

Answer 3

[inci]

Hello,

Thank you very much both for the answers! Following Sean's comment, I changed my code with the help of the solutions on the graphics challenge link and it seems to be working now.