Kivy - Binding a button in a popup - python-2.7

Question

I'm currently making a simple app in Kivy involving a Popup object containing a custom widget. I want to be able to access the information from the widget (button presses, etc) from the main screen, but I'm having issues with the button not being instantiated.
A (mostly) minimal (partially) working example is given below.
import kivy
kivy.require('1.9.1')
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.popup import Popup
from kivy.uix.checkbox import CheckBox
from kivy.uix.button import Button
from kivy.properties import ObjectProperty
from kivy.lang import Builder
Builder.load_string('''
<Main>
popup: popup
BoxLayout:
id: boxlayout
Button:
text: "Open Popup"
on_release: popup.open(); root.create_popup()
Popup:
id: popup
title: "Example popup"
on_parent: if self.parent == boxlayout: boxlayout.remove_widget(self)
PopupContent:
<PopupContent>:
closer: closer
# Suppose there is a more complicated nested layout structure here
BoxLayout:
orientation: 'vertical'
CheckBox:
Button:
id: closer
text: "Close popup"
''')
class PopupContent(BoxLayout):
def __init__(self,**kwargs):
super(PopupContent, self).__init__(**kwargs)
class Main(BoxLayout):
popup = ObjectProperty()
def __init__(self,**kwargs):
super(Main, self).__init__(**kwargs)
# Callback from button in PopupContent
def closer_callback(self,*args):
print("callback called!")
self.popup.dismiss()
# Creates container widget for popup and binds button to perform callback
def create_popup(self,*args):
popup_content = PopupContent()
popup_content.closer.bind(on_release = self.closer_callback)
# Problem: This returns "<type 'kivy.weakproxy.WeakProxy'>"
print(type(popup_content.closer))
class TestApp(App):
def build(self):
return Main()
if __name__ == '__main__':
TestApp().run()
As I annotated in my code, I attempted to bind the button in the PopupContent widget to run a method in my Main screen when pressed, but the button hasn't been created yet so no such binding is made.
How can I instead bind this button?

Answer 1

Turns out I had made a mistake when creating my example - although I created an instance of the PopupContent widget, I never added it to the Popup widget. Fixing that, it works fine now.
import kivy
kivy.require('1.9.1')
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.popup import Popup
from kivy.uix.checkbox import CheckBox
from kivy.uix.button import Button
from kivy.properties import ObjectProperty
from kivy.lang import Builder
Builder.load_string('''
<Main>
popup: popup
BoxLayout:
id: boxlayout
Button:
text: "Open Popup"
on_release: popup.open(); root.create_popup()
Popup:
id: popup
title: "Example popup"
on_parent: if self.parent == boxlayout: boxlayout.remove_widget(self)
<PopupContent>:
closer: closer
# Suppose there is a more complicated nested layout structure here
BoxLayout:
orientation: 'vertical'
CheckBox:
Button:
id: closer
text: "Close popup"
''')
class PopupContent(BoxLayout):
def __init__(self,**kwargs):
super(PopupContent, self).__init__(**kwargs)
class Main(BoxLayout):
popup = ObjectProperty()
def __init__(self,**kwargs):
super(Main, self).__init__(**kwargs)
# Callback from button in PopupContent
def closer_callback(self,*args):
print("callback called!")
self.popup.dismiss()
# Creates container widget for popup and binds button to perform callback
def create_popup(self,*args):
popup_content = PopupContent()
self.popup.content = popup_content
popup_content.closer.bind(on_release = self.closer_callback)
# Note: This still returns "<type 'kivy.weakproxy.WeakProxy'>"
# But the button is correctly bound regardless
print(type(popup_content.closer))
class TestApp(App):
def build(self):
return Main()
if __name__ == '__main__':
TestApp().run()
My understanding is that when the instance of PopupContent is first created, for performance reasons the actual widget isn't loaded until it is displayed (presumably via some load function). Until then however, we still get "weak references" via WeakProxy, which makes the binding possible.