MATLAB: Behavior of callback function

callbackMATLAB

Hello,
I wanted to break out of a while-loop when a pushbutton is clicked on a figure, so I wrote the code below.
function callbackTest1
uicontrol('Style','pushbutton',...
          'String','I''m done...',...
          'Position',[100 100 100 100], ...
          'Callback','pressed=1');
pressed = 0;
while(1)
    if pressed
        disp('button pressed')
        break
    end
    pause(0.1)
end
end
But, when I click the pushbutton, 'pressed=1' is displayed on command window and it does not get out of while loop.
In addition, it is suggested that 'disp('button pressed')' part can't be reached which I really don't understand.
On the other hand, the code below works as expected.
The only thing changed is that it's a script, not a function. Everything else is the same.
% callbackTest_script 
uicontrol('Style','pushbutton',...
          'String','I''m done...',...
          'Position',[100 100 100 100], ...
          'Callback','pressed=1');
pressed = 0;
while(1)
    if pressed
        disp('button pressed')
        break
    end
    pause(0.1)
end
Weird thing is that the same suggestion (disp('button pressed') can't be reached) is displayed but it works fine.
Finally, I figured out that I have to write the code like this.
function callbackTest2
uicontrol('Style','pushbutton',...
          'String','I''m done...',...
          'Position',[100 100 100 100], ...
          'Callback',@press);
      
pressed = 0;
    function press(~,~)
        pressed = 1;
    end
while(1)
    if pressed
        disp('button pressed')
        break
    end
    pause(0.1)
end
end
1) Why does callbackTest1 not work while callbackTest_script does?
2) In callbackTest1 and callbackTest_script, why can't "disp…" be reached?
3) Anything else I should know about what's behind the behavior of callback function?
4) Is there a better way to do this than callbackTest2?
Thank you.

Best Answer

'Callback','pressed=1'
Callbacks specified as character vectors are evalin('base') and so only affect the base workspace, not local variables.
You need to use one of the techniques to share variables; Share . Your callbackTest2 is an example of using a shared variable.
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