Can't get on_current_user to fire. Trying to figure out how to use EventDispatcher class.

demo.py

from kivy.uix.boxlayout import BoxLayout
from kivy.app import App
from kivy.uix.button import Button

from kivy.event import EventDispatcher
from kivy.properties import DictProperty

class UserManger(EventDispatcher):
    current_user = DictProperty({'rfid_tag': '', 'nickname': '', 'logged_in': False})

    # This never fires!
    def on_current_user(self, instance, value):
        print("Typical property change from", obj, "to", value)


class DemoBox(BoxLayout):

    # add a current user for the app
    current_user = UserManger()

    def __init__(self,**kw):
        """Constructor: make a new panel with a button"""
        super(DemoBox,self).__init__(**kw)
        
        button = Button(text='Click Me!',size_hint=(1,1))
        self.add_widget(button)
        
        # Set the callback function
        button.on_press = self.my_callback

    def my_callback(self):
        """Function to call when button is pressed."""
        print 'Hello World!'

        self.current_user.rfid_tag = 'ABCDEFG'
        self.current_user.nick_name = 'Santa Claus'
        self.current_user.logged_in = True
        print self.current_user.rfid_tag

        self.current_user.rfid_tag = 'QWERTY1'
        print self.current_user.rfid_tag
        print
        
class DemoApp(App):
    def build(self):
        return DemoBox()

if __name__ == "__main__":
    DemoApp().run()

from kivy.uix.boxlayout import BoxLayout
from kivy.app import App
from kivy.uix.button import Button

from kivy.event import EventDispatcher
from kivy.properties import DictProperty

class UserManger(EventDispatcher):
    current_user = DictProperty({'rfid_tag': '', 'nickname': '', 'logged_in': False})

    # This fires now, after much refactoring... Thanks rafalo1333!
    def on_current_user(self, instance, value):
        print "Typical property change from {} to {})".format(instance, value)


class DemoBox(BoxLayout):

    # add a current user for the app
    user_manager = UserManger()

    def __init__(self,**kw):
        """Constructor: make a new panel with a button"""
        super(DemoBox,self).__init__(**kw)

        button = Button(text='Click Me!',size_hint=(1,1))
        self.add_widget(button)

        # Set the callback function
        button.on_press = self.my_callback

    def my_callback(self):
        """Function to call when button is pressed."""
        print 'Hello World!'

        self.user_manager.current_user['rfid_tag'] = 'ABCDEFG'
        self.user_manager.current_user['nick_name'] = 'Santa Claus'
        self.user_manager.current_user['logged_in'] = True
        print self.user_manager.current_user['rfid_tag']

        self.user_manager.current_user['rfid_tag'] = 'QWERTY1'
        print self.user_manager.current_user['rfid_tag']
        print

class DemoApp(App):
    def build(self):
        return DemoBox()

if __name__ == "__main__":
    DemoApp().run()