[Kivy] Enable/Disable Button

# Special thanks to toto_tico
# http://stackoverflow.com/a/19881645

from kivy.uix.button import Button
from kivy.properties import BooleanProperty

class ButtonEx(Button):
    enabled = BooleanProperty(True)

    def on_enabled(self, instance, value):
        if value:
            self.background_color = [1,1,1,1]
            self.color = [1,1,1,1]
        else:
            self.background_color = [1,1,1,.3]
            self.color = [1,1,1,.5]

    def on_touch_down( self, touch ):
        if self.enabled:
            return super(self.__class__, self).on_touch_down(touch)