Lisning for a subclass property

I have a main class and a subclass and I would like to listen for the change in any of the subclass properties. In other term when the property in the subclass changes, I would like to trigger a function in the main class. I coded it this way but nothing is happening. thanks for your help.

mainclass =

classdef class_mainclass < handle

     properties (SetAccess = private)
     end

      properties (SetObservable)
          subclass;
      end

     events
     end

     methods

         function obj = class_mainclass
             obj.subclass = class_subclass;
             addlistener(obj,'subclass','PreSet',...
              @PushButton.do);
         end

         function do(src,evt)
             display('did');
         end

     end % methods
  end % classdef

and a subclass

classdef class_subclass < handle

     properties (SetAccess = private)
     end

      properties (SetAccess = public)
          A=1;
      end

     events
     end

     methods

         function obj = class_subclass
         end

         function obj = addA(obj)
             obj.A=obj.A+1;
         end

     end % methods
  end % classdef
>> m = class_mainclass;
>> m.subclass.addA

Answer 1

[Guillaume]

First, a matter of terminology. Your subclass is not a subclass at all. A subclass derives from the main class. In matlab OOP this implies the following definition:

classdef subclass < mainclass

Your subclass is just a standard class that happens to be a member of your main class. It would be very odd for a main class to instantiate a subclass (except through factory methods), anyway.

In any case, If you want to listen to the property changes of your member class, it is these properties you need to set observable and these properties you need to attach a listener. At present, the only thing you'll detect is if your subclass member is changed to a new instance. That is you'll detect this:

m.subclass = class_subclass; %assign a new class_subclass to the member property of m

[Walid]

Thanks for the very quick answer. as you can tell I am new at OOP in Matlab and not familier with syntax as much but wanted to move the project forward. I have previously tried addlistener(obj,'subclass.A','PreSet',... @PushButton.do); but that gave me an error

So not sure what is the correct syntax for checking on A from the mainclass.

[Guillaume]

The first thing you would have to do is add the SetObservable attribute to the property you want to listen to. In your example you'd modify class_subclass to

properties (SetObservable)
   A = 1;
end

You can then listen to it in your other class by changing your addlistener line to

   addlistener(obj, subclass, 'A', 'PreSet', @PushButton.do);

You'd have to do the same for the other properties of class_subclass.

I would also change the name of your classes. You don't have main class and subclass. Just two different classes. You also ought the make the subclass property of main class private (and rename that as well).

[Walid]

I implemented your recommendations and I got this error Undefined function or variable 'subclass'.

Error in class_mainclass (line 18) addlistener(obj,subclass,'A','PreSet',@class_mainclass.do);

I would appreciate your help.

[Guillaume]

Sorry, I made a typo. It should have read:

addlistener(obj.subclass, 'A', 'PreSet', @PushButton.do);

[Walid]

Thanks