Why do I get an error: "Invalid or deleted object"

I'm running the following simulation in MatLab:

for i=1:length(t)
    addpoints(curve1,posX(i),posY(i)); %trajectory in inertial frame
    ball1 = viscircles([posX(i) posY(i)],r,'LineWidth',4,'Color','black');
    framex=arrow([0 0],[R*cos(Theta(i)) R*sin(Theta(i))]);
    framey=arrow([0 0],[-R*sin(Theta(i)) R*cos(Theta(i))]);
  
    addpoints(curve2,X(i,1),X(i,2)); %trajectory in rotating frame
    ball2 = viscircles([X(i,1) X(i,2)],r,'LineWidth',4,'Color','black');
    
    if (posX(i))^2+(posY(i))^2 >= R^2
        delete(ball1);delete(ball2);
        break;
    end
    
    drawnow;
    pause(0.001);
    delete(ball1);delete(ball2);delete(framex);delete(framey);
    if ishghandle(curve1) == 0
        break;
    end
end

I tried to download the "arrow" function so I can be able to plot and update reference frames in my simulation. When the simulation runs to completion, everything is fine. However if I close the figure before the loop is completed, I get the error "Invalid or deleted object". The error points to the line where I call

    delete(ball1);delete(ball2);delete(framex);delete(framey);

So I pretty much know for a fact that this error arises from me deleting this arrow call in the loop, somehow it's deleting it before I close the figure, so it gives an error saying there's nothing to delete? I don't know why. I've been using the line function before just fine, but arrow gives an error. How come?

Answer 1

[Image Analyst]

We can't run your code because of missing variables. I'd bet you're trying to delete something that doesn't exist, but don't really care. The easy way is to just wrap the line in try catch and ignore errors

try
    delete(ball1);delete(ball2);delete(framex);delete(framey);
catch
end

Or you could use exist('ball1', 'var') to check for it in advance before deleting it.

if exist('ball1', 'var')
    delete('ball1');
end

Finally, you could try

drawnow;

to make sure that the graphics are actually drawn and exist before deleting.

[Walter Roberson]

You would test isvalid(ball1) or ishghandle(ball10 rather than whether ball1 exists as a variable.

[Denis Kartachov]

The first code you suggested worked perfectly, thank you very much