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State button callback- break while loop?

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Veena Chatti
Veena Chatti on 3 Sep 2020
Commented: Veena Chatti on 12 Sep 2020
Hi,
I'm trying to loop through hundreds of frames in a file with the push of a state button and the use of a slider in AppDesigner. With the code below, what I've managed so far is to get it to loop until the end of all frames and then stop.
What I'd like it to do further, however, is to loop continuously until the button is pressed, and stop looping by breaking the while loop when the button is un-pressed.
I would greatly appreciate all your tips and suggestions!
Thanks!
v = app.pswitch.Value;
switch v
case 0
% do nothing
case 1
j = get(app.Slider, 'Value');
while j < 300 % (number of frames)
if v == 1
% do this:
pause(1/1000)
j = get(app.Slider, 'Value');
app.Spinner.Value = j+1; % go to the next frame
app.Slider.Value = j+1; % go to the next frame
app.I = imshow(app.testrgb(:,:,3,j+1), [300 1300],...
'Parent', app.UIAxes); % display the next frame
end
end
app.Spinner.Value = 1;
app.Slider.Value = 1;
set(app.pswitch, 'Value', 0)
otherwise
% do nothing
end

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Accepted Answer

Rik
Rik on 3 Sep 2020
In general the solution to this is to use a flag that is controlled by your button. Then inside the while loop you check for that flag (a simple if flag,break,end will do).

  1 Comment

Veena Chatti
Veena Chatti on 3 Sep 2020
Thanks, I'd like to try this. Where can I find some tips about how to use a flag and have it under the control of the button?

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More Answers (1)

Mohammad Sami
Mohammad Sami on 3 Sep 2020
You can try something like this.
app.STOPButton.Enable = true;
app.STOPButton.Value = 0;
while(somecondition)
% do something
if(app.STOPButton.Value == 1)
break;
end
end
app.STOPButton.Enable = false;
app.STOPButton.Value = 0;

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Veena Chatti
Veena Chatti on 3 Sep 2020
Thanks, Mohammad and Rik! Yes, I am using a state button.
Setting a flag under the control of the button and using drawnow worked well. I also think your code would have worked, Mohammad, with drawnow.
Here's the functional code that I decided to use, in case anyone trying to do something similar comes across this thread:
value = app.pswitch.Value;
j = get(app.Spinner, 'Value');
set(app.pswitch, 'Text', 'Pause');
flag = 1; % Set flag
while(flag) && j < 299
pause(1/1000)
j = get(app.Spinner, 'Value');
set(app.Spinner, 'Value', j+1);
set(app.Slider, 'Value', j+1);
app.I = imshow(app.testrgb(:,:,3,j+1), [300 1300],...
'Parent', app.UIAxes); % Display command
drawnow; % get it to check
f = get(app.pswitch,'Value');
if isequal(f, 0)
set(app.pswitch, 'Text', 'Play');
flag = 0;
break;
elseif ~isequal(f,1)
set(app.pswitch, 'Text', 'Pause');
end
end
This is a bit off topic, but do either of you (or anyone else who sees this) know the smallest time interval and resolution it's possible to set with pause()?
Rik
Rik on 3 Sep 2020
The theoretical limit would be eps. As a practical limit I would suggest 30ms.
It isn't hard to test this, just use a loop to make the time smaller until tic,toc is telling you the pause is much longer than the time you asked for. I you want I can write some code for you. I'm currently on mobile so writing an example is more challenging.

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