State button callback- break while loop?

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
    
    

Answer 1

[Rik]

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).

[Veena Chatti]

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?

Answer 2

[Mohammad Sami]

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;

[Veena Chatti]

Thanks, I tried this, but it still goes through the whole while loop, and doesn't stop in between even if the button is pushed again.

[Rik]

I don't have much experience with AppDesigner, but I would have expected the code from Mohammad to work. You might need drawnow in your while loop to force Matlab to execute queued callbacks.

[Mohammad Sami]

Are you using a state button ? The code is written for use with state button.

If that does not work, you can use drawnow as suggested by Rik.

[Veena Chatti]

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]

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.

[Veena Chatti]

Thank you! I figured it out.