How to store ROS callback data in class properties?

2 min readMay 4, 2023

I am trying to store a callback data from ROS’s topic called /scan in a properties (laser) of class that I created.

I got an error like this:

"No public field laser exists for class robotics.ros.Subscriber.

Error in MobileRobot/Callback_Laser (line 14) obj.laser = [message.Ranges];Error in @(varargin)robot.Callback_Laser(varargin{:})Error in robotics.ros.internal.onNewMessageCallback (line 44) feval(callbackFcn, source, message, userData{:});

Warning: Error occurred while evaluating listener callback.”

Where is my mistake e how can I store a the callback data in a properties class?

Next the code class.

classdef MobileRobot < handle
  properties(Access = public)
      odom=[];
      laser = [];
  end

    methods(Access = public)
        function obj = MobileRobot()  % Constructor   
        end        function  Callback_Laser(~, obj, message)
           % global laser
           % laser = [message.Ranges]; 
            obj.laser = [message.Ranges];
        end
    end
end

and the main code

clear all;close all;clc;
 rosinit

 global rosMasterIp;
 rosMasterIp = 'http://192.168.0.113:11311'; global localhostIp;
 localhostIp = '192.168.0.113'; global robot;
 robot = MobileRobot(); set_pose = robotics.ros.Node('getLaser',rosMasterIp,'NodeHost' , localhostIp);
 subs = rossubscriber('/scan',@robot.Callback_Laser);

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The issue here seems to be that the callback tied to rossubscriber is required to have 2 inputs “src” and “msg”, where “src” is the subscriber itself and “msg” is the message received.

Notice that the way you have defined your Callback_laser method, “obj” isn’t the instance of the class, but rather a reference to the subscriber… which, as the error message suggests, does not have a “laser” property.

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