Pause execution of While loop and resume from the same point with PushButtons App Designer

Hi! I made an animation in AppDesigner with a while loop, I pause and resume it with push buttons using uiwait and uiresume in their callbacks, apparently it works because when I hit "pause" the image freezes but when I push the "resume" button it seems the while loop kept running because by that time the animation has already advanced like it jumped in time from an image to another.

I saw in another post

How can I do to pause the while loop and then resume from the same point I paused it??

I would really appreciate any suggestion

 function StartButtonPushed(app, event)
            
            close all
            set(app.StartButton,'Text','Restart')
            time = 120;                                            
            set(app.UIAxes, 'units','points')
            cla(app.UIAxes);
               
             R = 65;                                               
   
             ang=linspace(0,2*pi,50);              
             xp=R*cos(ang);                        
             yp=R*sin(ang);                        
                                    
                % Animation
                
                % Draw outter circle
                patch(app.UIAxes,xp,yp,'w')
                hold(app.UIAxes,'on');
                axis(app.UIAxes, 'equal');
                
                % line
                rho1 = 55;                            
                line = plot(app.UIAxes,NaN, NaN,'-*', 'LineWidth', 5, 'MarkerSize', 0.5, 'color', 'k');

                              
                tic
                while   toc < time
                  
                t1=toc;
                f = 0.2*360;
                line.XData = [0, rho1*cosd(-f*t1)] ;
                line.YData = [0, rho1*sind(-f*t1)] ;
                                                      
                drawnow  
                end

        end

        % Button pushed function: PauseButton
        function PauseButtonPushed(app, event)
            uiwait(app.animation)
        end

        % Button pushed function: ResumeButton
        function ResumeButtonPushed(app, event)
            uiresume(app.animation)
        end
    end

Answer 1

[Rik]

The reason for your issue is that you're using toc, which will still continue running.

If you measure how long your GUI has been paused, you can store that in a property. If you subtract that from t1, you can effectively pause the time.

See the code below for my suggestion. You should also consider always using an explicit handle for toc. Otherwise you will measure the time since the last tic, not the matching call.

                t_h=tic;app.PauseTime=0;
                while true
                    t1=toc(t_h)-app.PauseTime;
                    if t1>time,break,end
                    
                    f = 0.2*360;
                    line.XData = [0, rho1*cosd(-f*t1)] ;
                    line.YData = [0, rho1*sind(-f*t1)] ;
                                                      
                    drawnow  
                end
        end
        % Button pushed function: PauseButton
        function PauseButtonPushed(app, event)
            app.PauseHandle=tic;
            uiwait(app.animation)
        end
        % Button pushed function: ResumeButton
        function ResumeButtonPushed(app, event)
            app.PauseTime=app.PauseTime+toc(app.PauseHandle)
            uiresume(app.animation)
        end

[MSolano]

Wow, your answer is great! Thank you!

I changed the code and it's not recognazing the app.PauseTime (Unrecognized property 'PauseTime' for class 'Animation_'.), I'm sorry I'm new in matlab and I don´t fully understand what are app.PauseTime and app.PauseHandle for, are they the properties where I store the time data? Is not the same as if I write just PauseTime or PauseHandle?

[Rik]

You need to define them as properties. There should be a button somewhere in AppDesigner to do so. One stores the total time paused, and the other stores the handle to the tic so you can accurately track the time.

[Rik]

Why are you using ==? And why are you ignoring my advice to store these variables in properties?

I also noticed that there should be a change to my answer:

while (toc(t_h)-app.PauseTime) < time
    t1=toc(t_h)-app.PauseTime;

[MSolano]

yeah, sorry I hadn't understand how to set them as properties but It works now with your advice. Thank you!!!

[Rik]

No problem, as long as it is fixed now.

I have slightly edited my answer to make it easier to maintain.

[Karthikeyan Deivamani]

Hi, Is there any possibilty of pausing and resuming from the last point with out using App designed but with MATLAB code. I have been trying using waitforbuttompress and pause but I hit a roadblock everytime. I could make my visual simulation pause but make it resume from the last point.

[Rik]

You need an explicit position to pause your execution. What you can do is creating a while loop with a pause of a few seconds. That way you can check the flag every few seconds and resume from that point, without using too many resources.

This is the easy way. The hard way is to write your code in such a way that your code can resume your simulation. That will require you to write your code in such a way that it can simply calculate the next iteration based on the last one.