Timer function in OOP object constructor not working as expected

Hello,

I have some oop code that talks to an instrument over a serial port. I want to continually monitor for and handle messages from the instrument. I had intended to do this by setting up a timer in the constructor that calls a read/handle buffer function, but I found that timer objects defined in the constructor do not behave the way I normally expect.

The code below*1 (not full .m file) successfylly prints tick at the desired interval, but if I replace 'disp(''tick'')' with @demofunc, I get the following error*2.

Why does this happen, and how can I define a timer callback effectively through/within an object constructor? Thanks, Sean

*1

 classdef zbrlinact2
      properties
          comobj=[];
          expected_responses=[];
          readmesgtimer=[];
      end
      methods
          %(zbrlinact) function call
          %This function is used to create the object and initialize the comm
          %port for communication with the linear actuators.
          function obj = zbrlinact2()
              obj.comobj = serial('COM1','BaudRate',9600,'DataBits',8,'Parity', 'none', 'StopBits', 1);
              fopen(obj.comobj);
              obj.readmesgtimer = timer(  'BusyMode', 'queue', ...
                                          'ExecutionMode', 'fixedSpacing', ...
                                          'TimerFcn', 'disp(''tick'')', ...
                                          'ErrorFcn', 'disp(''error'')', ...
                                          'Period', 0.1);
              start(obj.readmesgtimer);

              function demofunc()
                  disp('read');
              end

          end

*2

Error while evaluating TimerFcn for timer 'timer-2'

Too many input arguments.

error

Answer 1

[Sean de Wolski]

The timer passes two input arguments to its timerfcn. The function you are using must be able to accept these.

function demo_func(obj,evt);
  disp('read')
end

You could also just denyt he inputs:

function demo_func(~,~);
  disp('read')
end

Answer 2

[Walter Roberson]

A time callback specified as a function handle will still be called in standard callback style, with two arguments automatically added at the beginning. If your demofunction routine does not expect at least two arguments you would get the error you note.