how to add listener and action when listener detected

i created a class which plots an image from 3d image matrix [img row size, img cols size , frame num] which have shared data (=staticprop) , shared between all instantes of the class.

this looked something like this:

classdef MyClass  < handle
    
    properties (Constant, GetAccess = private)
        staticprop = containers.Map; %or just make a lightweight handle class
    end
    
    properties
       ...
        currFrameCounter=1
        images=[];
    ...
    end

methods
    function obj = MyClass(inputFrameCounter,input_images)
        obj.images=input_images;
        
        tmp=obj.staticprop;
        if isempty(tmp)
        tmp('currFrameCounter')=inputFrameCounter;
        end
        obj.currFrameCounter=inputFrameCounter %% so currFrameCounter will be "local" variable to the instantiation of the class, and 
        %% staticprop will be shared data to all of the instantiation of myClass.        
        
     end
end

function ShowIMG(obj,frame)
    tmp=obj.staticprop;
    imshow(obj.images(:,:, frame))
    
end

function keyPressFunc(obj)
   %% change "shared" and local currFrameCounter when key pressed
   tmp=obj.staticprop;
    tmp('currFrameCounter')= some other value , say  , tmp('currFrameCounter')+1
     obj.currFrameCounter=tmp('currFrameCounter')
     
     ShowIMG(tmp('currFrameCounter')); %%update the figure;
end


end
  

now I am creating 2 diffrent instantes to the same class, each conatins diffrent images.

I want to add event ( or listenerlistener, I really dont know how it is called) so that every time there is a change in the shared variable " tmp('currFrameCounter')" I will update the figure.

for example, if

a1=MyClass(1,input_images1);

a1.ShowIMG(1);

a2=MyClass(1,input_images2);

a2.ShowIMG(1);

in case i pressed on the "right arrow" of the figure of a1, the a1 figure was updated,

and I want that a2 will be updated automatically (update function will be called).

( this can be detected using the local obj.currFrameCounter. every time obj.currFrameCounter~=tmp('currFrameCounter') I want to call a function which will update my figures. )

can someone provied me with a simple examle?