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Why the loop does not stopped?

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Using designer, I make same program as below.
When click 'Run Start', current time and loop running count will be described at 'Run Count' and 'Run Time'.
When click 'Run Stop', running loop will be stopped.
So I programmed as below.
% Button pushed function: btnStart
function btnStartPushed(app, event)
app.btnStart.Enable = 'off';
app.btnStop.Enable = 'on';
runCount = 0;
runTime = datestr(now, 'HH:MM:SS');
global runStatus
runStatus = 0;
set(gcf, 'WindowButtonUpFcn', @btnStopButtonPushed)
while ~runStatus
app.efRunCount.Value = num2str(runCount);
app.efRunTime.Value = runTime;
runCount = runCount + 1;
runTime = datestr(now, 'HH:MM:SS');
app.btnStart.Enable = 'on';
app.btnStop.Enable = 'off';
% Button pushed function: btnStop
function btnStopButtonPushed(app, event)
global runStatus
runStatus = 1;
I got this kind of method from this site.
Why I use 'drawnow' order in this program?
When I remove 'drawnow' because I have own windows, the loop is not stopped even through 'Run Stop' is clicked.
How can I handle this problem?

Accepted Answer

Ben Cunningham
Ben Cunningham on 16 Apr 2019
See the 'interruptible' property of callbacks in app designer - e.g. here under the heading 'Callback execution control'.
The answer to your question is :
"The interruption occurs at the next point where MATLAB processes the queue, such as when there is a drawnow, figure, uifigure, getframe, waitfor, or pause command."
In other words the drawnow command is providing an oppurtunity for your stop button to interrupt the execution of the while loop to set the global variable, then when the while loop resumes ~runStatus will evaluate false.
Without drawnow, the stop button will wait until the previous callback is finished - which never occurs since your while loop will spin forever.
Ben Cunningham
Ben Cunningham on 17 Apr 2019
Well figured out! No worries.

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