Behavior of callback function?

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.

Answer 1

[Walter Roberson]

'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.

[lazymatlab]

Thanks! (especially for the faq page!)