KV file popup does not respond with proper action - kivy

Question

My popup.KV file content:
<ConfirmPopup>:
cols:1
Label:
text: root.text
canvas.before:
Color:
rgba: 1, 0, 1, 0.4
Rectangle:
size: self.size
pos: self.pos
GridLayout:
cols: 2
size_hint_y: None
height: '44sp'
Button:
text: 'Yes'
canvas.before:
Color:
rgba: 0, 1, 0, 1
Rectangle:
size: self.size
pos: self.pos
on_release: root.dispatch('on_answer','yes')
Button:
text: 'No'
canvas.before:
Color:
rgba: 1, 0, 0, 1
Rectangle:
size: self.size
pos: self.pos
on_release: root.dispatch('on_answer', 'no')
and the popup.PY file:
from kivy.lang import Builder
from kivy.uix.gridlayout import GridLayout
from kivy.uix.popup import Popup
from kivy.properties import StringProperty
class ConfirmPopup(GridLayout):
text = StringProperty('AAAA')
def __init__(self, **kwargs):
self.register_event_type('on_answer')
super(ConfirmPopup, self).__init__(**kwargs)
def on_answer(self, *args):
pass
class PopupTest():
def __init__(self):
self.popup = None
def build(self):
Builder.load_file('popup.kv')
content = ConfirmPopup(text='Do You Love Kivy?')
content.bind(on_answer=self._on_answer)
self.popup = Popup(title="Answer Question",
content=content,
size_hint=(None, None),
size=(480, 400),
auto_dismiss=False)
self.popup.open()
def _on_answer(self, instance, answer):
print("USER ANSWER: ", repr(answer))
self.popup.dismiss()
def show():
pop = PopupTest()
pop.build()
THis is the app.py file that uses the popup
import kivy
from kivy.app import App
from popup import *
class PopTest(App):
show()
if __name__ == '__main__':
PopTest().run()
My problem is that the popup displays correctly, the buttons blink when clicked BUT the appropriate message is not printed and the popup is not dismissed when a button is clicked. To me it looks like the button event is not bound to the actions. How do I fix it.
Thanks for a fix and any explanations.

Answer 1

Your PopupTest class must be an EventDispatcher in order for your code to work as you want. Just modify PopupTest slightly:
class PopupTest(Widget):
def __init__(self):
super(PopupTest, self).__init__()
self.popup = None