You are very close to having it working! In your Notify callback, you make a call to the constructor ClassA rather than a specifieid object of type ClassA. So you would give the argument to the ClassB constructor to pass an object of type ClassA and then reference that object instead of the class constructor:
classdef ClassB < handle
properties
button
end
methods
function o = ClassB(classAObj)
fig = figure;
o.button = uicontrol(fig,'Style','pushbutton','Callback',@(~,~,~) notify(classAObj,'EventA'));
end
end
end
