Timer not working in my programmatic app (not app designer)

I have a programmatic app where I'm trying to periodically and automatically update a plot. Whenever I use the start(timer_object) it produces a message "Dot indexing is not supported for variables of this type". Here's the app:

Answer 1

[Voss]

First, line 25:

%update_timer = data.update_timer;

needs to be uncommented for that error to happen (otherwise you get a different error because "update_timer" is undefined).

Errors in timer callbacks can be tricky to debug because the error message doesn't tell you what line it happened on. To debug it, you can put a breakpoint on the first line of the TimerFcn (axTimerFcn) and step through until you get the error. When you do that, you'll find that this line (line 31)

fig = ancestor(src,"figure","toplevel");

gives fig as an empty array [], which causes the error on the next line when you try to access fig.UserData. fig is empty because timers don't exist inside a figure the way uicontrols do, so ancestor is not going to work for them. You could use timerfind or timerfindall to find your timer object, but I recommend restructuring your code so that the callbacks (the uibutton ButtonPushedFcn StartTimer and the TimerFcn axTimerFcn) are nested inside the main function timer_app_1. Then they'll easily have access to whatever they need and it will no longer be necessary to have to store anything in the figure's UserData. Something like this:

function timer_app_1

fig = uifigure('Position',[100 50 2400 3.5*430],'AutoResizeChildren','off');
grid = uigridlayout(fig, [3 3]);
ax = uiaxes(grid);
ax.Layout.Column = 2;
ax.Layout.Row = 2;

uibutton(grid,"Text","Start Timer","ButtonPushedFcn",@StartTimer);

update_timer = timer('ExecutionMode', 'fixedRate', ...    % Run timer repeatedly
                'Period', 1, ...                     % Period is 1 second
                'BusyMode', 'queue',...              % Queue timer callbacks when busy
                'TimerFcn', @axTimerFcn);
%start(update_timer);
i=1;


    function StartTimer(~,~)
        start(update_timer)
    end


    function axTimerFcn(~,~)
        i=i+1;
        plot(ax,1:10,i.*ones(1,10))
        if i==10
            stop(update_timer)
        end
    end

end

See: https://www.mathworks.com/help/matlab/matlab_prog/nested-functions.html

[Brendan Hall]

Oh ya my bad, that "%" wasn't there when I got the error message. That's interesting though I'll try to nest the function like you're saying.

[Brendan Hall]

Thanks!

[Voss]

You're welcome!

Answer 2

[Walter Roberson]

The first parameter passed to a timer is the timer object, and the second parameter is the event data.

You are trying to

fig = ancestor(src,"figure","toplevel");

which is assuming that the first parameter is a graphics object rather than a timer object.

The easiest workaround is to use

update_timer = timer('ExecutionMode', 'fixedRate', ...    % Run timer repeatedly
                'Period', 1, ...                     % Period is 1 second
                'BusyMode', 'queue',...              % Queue timer callbacks when busy
                'TimerFcn', @(src,event)axTimerFcn(fig,event));

so that fig gets passed as the first parameter to the callback function.

[Brendan Hall]

Thanks!!