Problem with Events and Callbacks

Hello Everyone,

I am trying to use Events in MATLAB. I have created two classes. The first class(called: WSN_ENV) is responsible to build the object(nodes) for the second class(called: normal_node). The normal_node class is added to the event listeners which were created in the WSN_ENV. The problem is that when I want to trigger the event (by calling timer function from WSN_ENV) I get:

Warning: Error occurred while executing callback: Error using normal_node.timer Too many input arguments.

Here is my code for both classes. I really don't know what is the problem!

classdef WSN_ENV < handle 
   properties(GetAccess = 'public', SetAccess = 'public')
       Number_of_BS=0;
       Number_of_node=0;
       global_timer=0;
       node_obj=normal_node.empty;
   end
   events(ListenAccess = 'public', NotifyAccess = 'public')
       time_event;
   end
   methods
%==========================================================================
% Constructor:
       function src=WSN_ENV(BS,Node)
           src.Number_of_BS=BS;
           src.Number_of_node= Node;
          for i=1:Node
              src.node_obj(i)= normal_node(src,i);
          end
       end       
%==========================================================================
       function timer(obj)
            obj.global_timer = obj.global_timer + 1;
            notify(obj,'time_event'); % Broadcast notice of event
       end
end
end

and the second Class:

classdef normal_node < handle 
   properties(GetAccess = 'public', SetAccess = 'public')
       ID=0;
       RF_stat='power_off';% power_on, listening
       PWR_stat='sleep';% power_on
       rx_buffer= 0;
       tx_buffer= 0;
       data=0;
       local_timer=0;
       watch_dog=0;
   end
   methods (Access ='public')
%==========================================================================
% Constructor:
       function src=normal_node(ENV_obj,ID)
           src.ID=ID;
           src.RF_stat= 'power_on';
           src.PWR_stat= 'power_on';
           addlistener(ENV_obj,'time_event',@normal_node.timer);
       end       
   end
 methods (Static)
       function obj=timer(obj)
           obj.local_timer=obj.local_timer+1;
       end
 end
end