cancelling waitbar insdie a gui function

Hello everyone, I am having some problem with waitbar defined inside a gui script. The problem is I have created a waitbar with cancel option which was working fine outside. But when I pasted it inside my gui.m script the cancel button is not working (rest all is fine). Below is the code I have used:

pvh=waitbar(0,'calculating.....','name','ESTIMATION',...
    'createcancelbtn','setappdata(pvh,''cancel_callback'',1)');
setappdata(pvh,'cancel_callback',0);

for count_i1 = 1:l_count

        if getappdata(pvh,'cancel_callback')==1
          errordlg('Stopped by user');    
          break;
      end

      waitbar(count_i1/ l_count,pvh,sprintf('Calculating %d  %s %d',count_i1,'of', l_count))

I went through some help of MATLAB and tried some options like drawnow or updating the handles of the waitbar figure. Looks like I did not do it properly. Any suggestions on how to make it work? thanks in advance.

Answer 1

[Jan]

You cannot access the handle pvh from the callback, when it is defined as a string. Callbacks defines as a string are evaluated in the baseworkspace, where "phv" is not known. I'd expect an error message then.

Unfortunately the documentation of waitbar mentions a string-callback only. Using a function handle would be smarter. Try this:

pvh = waitbar(0, 'calculating.....', 'name', 'ESTIMATION',...
              'createcancelbtn', @myCancelCB);
setappdata(pvh, 'cancel_callback', 0);
for count_i1 = 1:l_count
  drawnow;
  if getappdata(pvh, 'cancel_callback') == 1
    errordlg('Stopped by user');    
    break;  % Stop the loop: for coubnt_i1
  end
  ...
end

function myCancelCB(hObject, EventData)
phv = ancestor(hObject, 'figure');
setappdata(phv, 'cancel_callback', 1);
end

This is somewhat longer than defining the callback as string, but much safer, because it does not pollute the baseworkspace.

[Shravan Kumar]

Thank you for the solution Jan. I tried it and its just working fine. I have one small question, how did it work when defined in a script but not in gui.m. I defined this in the main call back function (inside gui) only right. so it did not need to update the handles right? yes, I also got the error as you said that undefined variable pvh. I went through the documentation of ancestor and got how this logic is working. Thanks again. For people who want to use the @myCancelCB function please remove the 'end' from the function. works fine.

[Jan]

The trailing "end" is required, if any function of the M-file has one or if it is a nested function. In other cases it should be omitted.

I do not understand exactly what "inside gui" means. The show code works in a script also, but in older Matlab versions you have to define the function for the callback in a separate file.

Where did you "update the handles"?

The general suggestions are:

• Functions are more stable than scripts, so use scripts for short hacks only, while functions are preferred for productive work.
• Define callbacks by function handles, because the evaluation of strings is prone to bugs and hard to debug.