Timer stop function // findobj returns nothing

Hi, I constructed a timer to run a countdown, at the beginning of the countdown I want to turn a UserData variable to 'on'. At the end of the countdown I want it back to 'off'. My actuall code looks like that:

t = timer('Period', 1, 'TasksToExecute', stop_in_sec, 'ExecutionMode', 'fixedRate', 'ObjectVisibility', 'off'); 
t.StartFcn = { @run_timer, handles.Countdown_edit, 'Countdown started:'}; 
t.StopFcn  = { @run_timer, handles.Countdown_edit, 'Countdown stopped'}; 
t.TimerFcn = { @run_timer, handles.Countdown_edit, ''}; 
t.UserData = stop_in_sec; 
start(t)

and the timer callback:

function run_timer(t,event,Countdown_edit, varargin) 

    switch event.Type 
       case 'StopFcn' 
          Schalter = get(findobj('Tag', 'LiveCam_Tool'), 'UserData');
          Schalter.xyz = 'on';
          set(Countdown_edit, 'str', '-----');
          delete(t); 

       case 'StartFcn' 
          Schalter = get(findobj('Tag', 'LiveCam_Tool'), 'UserData');
          Schalter.xyz = 'off';

       case 'TimerFcn' 
          set(Countdown_edit, 'str', t.UserData); 
          t.UserData= t.UserData-1;       
    end

After placing breakpoints in StopFcn, StartFcn and TimerFcn the programm was running. If I just place them in one or two Fcn's the "get(findobj('Tag', 'LiveCam_Tool'), 'UserData');" in StopFcn returns nothing. (The same in the StartFcn is still working!) Who can help me?

Answer 1

[Walter Roberson]

The object might have a hidden handle, or might have a handle visible in callbacks. Try replacing findobj() with findall()

[Adrian]

It tells me: Invalid handles passed to findall.

And now its not even running with breakpoints.