Set Function Not Workin Normal Execution

I tried to update my listbox with using the code below.

set (findobj(gcf,'tag','listbox1'),'string','');

But it is not working. When i go to debug mode and put a breakpoint before this code. It update listbox with blank value. I also tried with a proper string like "Hello World" but it still not work in normal executaion. How can i handle this problem ?

[dpb]

See if https://www.mathworks.com/matlabcentral/answers/378766-a-static-text-does-not-update-after-set-until-the-callback-has-finished?s_tid=answers_rc1-1_p1_MLT provides a clue...

[Volkan Sahin]

Hi, Thank you for your help. The solution you have offered works for updating figure. But unfortunatelly is doesn't work for updating listbox element.