MATLAB: Timer error: Cannot start timer because it is already running.

callbacktimer

I am trying to implement a simple timer in a GUI. It is just a figure with two buttons. I want when I press the start button to execute the updaterFcn callback function of timer. When I push the stop button I want the timer to stop. That's all. However, I get the following error (and I don't know why):

Error while evaluating StartFcn for timer 'timer-2' 
Cannot start timer because it is already running.

This is my function

function stopwatch
S.fh = figure('units','pixels',...
              'position',[300 300 400 400],...
              'menubar','none',...
              'name','stopwatch',...
              'numbertitle','off');
S.pb(1) = uicontrol('style','push',...
                    'units','pixels',...
                    'position',[10 10 85 30],...
                    'fontsize',14,...
                    'string','start',...
                    'CallBack',@switchon);
S.pb(2) = uicontrol('style','push',...
                    'units','pixels',...
                    'position',[105 10 85 30],...
                    'fonts',14,...
                    'str','stop',...
                    'CallBack',@switchoff);
tmr = timer('Period',1,...  
            'TimerFcn',@updater,...
            'StopFcn',@switchoff,...
            'StartFcn',@switchon);
      function updater(varargin)
          disp('Timer!')
      end
      function switchon(varargin)
          start(tmr)
      end
      function switchoff(varargin)
          stop(tmr)
  %         delete(tmr)
      end

Best Answer

There are two problems with your timer:

The values of StopFcn causes stop(tmr) in switchoff to call stop a second time and correspondingly with StartFcn
ExecutionMode must be set to get more than one call by the timer

Try to replace your timer definition by

    tmr = timer( 'Period'       , 1             ...
               , 'BusyMode'     , 'drop'        ...
               , 'ExecutionMode', 'fixedDelay'  ...
               , 'TimerFcn'     , @updater      );

Related Solutions

MATLAB: Stop timer

Your timer function @axes1.handles is completly invalid, it's no function.

Also the way you start and stop the timer isn't correct, should give you too many errors.

Here's a GUI that I made with GUIDE, the fig file is just one axes and one pushbutton, the m file code is:

function varargout = rottest(varargin)
% ROTTEST M-file for rottest.fig
%      ROTTEST, by itself, creates a new ROTTEST or raises the existing
%      singleton*.
%




%      H = ROTTEST returns the handle to a new ROTTEST or the handle to
%      the existing singleton*.
%
%      ROTTEST('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in ROTTEST.M with the given input arguments.
%
%      ROTTEST('Property','Value',...) creates a new ROTTEST or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before rottest_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to rottest_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES
% Edit the above text to modify the response to help rottest
% Last Modified by GUIDE v2.5 04-Jun-2011 18:27:20
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @rottest_OpeningFcn, ...
                   'gui_OutputFcn',  @rottest_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
% --- Executes just before rottest is made visible.
function rottest_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure

% eventdata  reserved - to be defined in a future version of MATLAB



% handles    structure with handles and user data (see GUIDATA)



% varargin   command line arguments to rottest (see VARARGIN)
% Choose default command line output for rottest
handles.output = hObject;
spy %just to put something in the axes so we can see it rotating
MyTimer=timer('TimerFcn',@RotImgFcn,'BusyMode','queue','executionmode','fixedspacing','period',0.5);
%tag the timer and axes to have easy access to their handles
set(MyTimer,'tag','MyTimer')
set(handles.axes1,'tag','MyAxes')
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes rottest wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = rottest_OutputFcn(hObject, eventdata, handles) 
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
MyTimer=timerfind('tag','MyTimer');
MyTimerStatus=get(MyTimer,'Running');
if strcmp(MyTimerStatus,'off')
start(MyTimer)
else
stop(MyTimer)
end
function RotImgFcn(a,b)
%this function does the rotation
camorbit(findall(0,'tag','MyAxes'),1,0,'data',[0 0 1]); 
% --- Executes when user attempts to close figure1.
function figure1_CloseRequestFcn(hObject, eventdata, handles)
% hObject    handle to figure1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% when the user closes the GUI it stops the timer if it is running
% and deletes the timer from memory
MyTimer=timerfind('tag','MyTimer');
MyTimerStatus=get(MyTimer,'Running');
if strcmp(MyTimerStatus,'on')
stop(MyTimer)
end
delete(timerfind('tag','MyTimer')); %delete our timer
%delete(timerfindall) %delete all timer objects
% Hint: delete(hObject) closes the figure
delete(hObject);

MATLAB: Varying timer’s period inside the TimerFcn

This page mentions an approach to vary the period of timer: https://stackoverflow.com/questions/15576682/matlab-change-repeating-timer-period

Here I show the method mentioned in the second answer. This example sets a random time period between 1 to 5 seconds after each callback of timer.

t = timer('StartDelay', 1, 'TimerFcn', @timerFcn, ...
    'StopFcn', @timerStopFcn, 'ExecutionMode', 'singleShot');
start(t);
function timerFcn(obj, ~)
    disp(obj.StartDelay)
end
function timerStopFcn(obj, ~)
    period = randi([1 5]);
    obj.StartDelay = period;
    start(obj);
end

Best Answer

Related Solutions

MATLAB: Stop timer

MATLAB: Varying timer’s period inside the TimerFcn

Related Question