Kivy, passing argument using roulette and carousel - kivy

Question

main:
# -*- coding: utf-8 -*-
import kivy
kivy.require('1.8.0')
'''
Check aida.kv for the ui design
'''
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import (ObjectProperty, ListProperty, StringProperty, NumericProperty)
class Controls(BoxLayout):
timer_value = NumericProperty()
def __init__(self, **kwargs):
super(Controls, self).__init__(**kwargs)
self.roulette_time.bind(rolling_value=self.time_changed)
def time_changed(self, instance, value):
self.timer_value = value
class WeatherRoot(BoxLayout):
pass
class AidaApp(App):
pass
if __name__ == '__main__':
AidaApp().run()
kv:
# -*- coding: cp1252 -*-
#:kivy 1.8.0
#:import CyclicRoulette kivy.garden.roulette.CyclicRoulette
WeatherRoot:
<WeatherRoot#BoxLayout>:
carousel: carousel
controls: controls
BoxLayout:
orientation: "vertical"
Carousel:
id: carousel
Controls:
id: controls
<Controls>:
canvas.before:
Color:
rgba: 0.686, 0.635, 0.541, 0.5
Rectangle:
pos: self.pos
size: self.size
roulette_time: rlt_time
BoxLayout:
CyclicRoulette:
cycle: 60
density: 15
zero_indexed: True
selected_value: 5
width: 50
background_color: [0.686, 0.635, 0.541, 1]
id: rlt_time
Label:
size_hint: (1, .8)
text: format(root.timer_value)
font_size: 50
I get an error 'Controls'object has no attribute 'roulette_time
When I set an attribute I get sort of different errors about binding, etc
only works when in kv Controls set to root, but I must have a different class as a root
Please help me to solve this problem, I am stucked

Answer 1

You get the error Controls'object has no attribute 'roulette_time' because nowhere in your Controls class, or anywhere for that matter, do you define a roulette_time variable. Try setting roulette_time = NumericProperty(0) in the Controls class.
class Controls(BoxLayout):
roulette_time = NumericProperty(0)

Answer 2

Not sure why that's not working, because it should. An ObjectProperty should automatically be created to hold the reference to the CyclicRoulette instance.
But - there's an easier way to do this! You're just updating a property on your Controls class with that value anyway, so you can directly bind them. Replace this line:
roulette_time: rlt_time
with:
timer_value: rlt_time.rolling_value
and whenever the CyclicRoulettes rolling_value property changes, your timer_value on Controls will automatically be updated. You don't need to create the time_changed method or bind it to the CyclicRoulette.