Kivy Factory and Kivy Language demo

factory_kvlang.py

from kivy.base import runTouchApp
from kivy.lang import Builder
from kivy.factory import Factory

# ----------------------------------------
# Widget classnames MUST start uppercase
# Kivy property names MUST start lowercase
# ----------------------------------------
# WOW 1: Subclassing Magic (doesn't exist yet) + using mixin
# WOW 2: Creating new Kivy property "feet" for class Rabbit
# WOW 3: kvlang auto-listens to changes in Kivy property "feet"
#        (text property is inherited from Label via Magic)
# WOW 4: Declare multiple callbacks for same event
#        (on_press event is from ButtonBehavior mixin)
# WOW 5: Multi-line callback function (no further indents possible)
# WOW 6: Kivy properties emit events when they change, the
#        event name is always on_<propertyname>
Builder.load_string('''
<Rabbit@ButtonBehavior+Magic>: # WOW1
    feet: 4 # WOW2
    text: 'Rabbit with {} feet'.format(self.feet) # WOW3
    on_press: print('a callback') # WOW4 (with next line)
    on_press:
        self.feet = (self.feet + 1) % 5
        print("set feet: {}".format(self.feet)) # WOW5
    on_feet:
        print("recv feet: {}".format(self.feet)) # WOW6
''')

# WOW 7: Factory returns class objects registered with a
# particular name (which is a string, "Label" in this case).
class Magic(Factory.Label):
   pass

# This is essentially the same as Factory.Label above, it
# returns the GridLayout class, but here we create an instance
# instead of inheriting (ie using function call syntax)
wow = Factory.GridLayout(cols=1)

# WOW 8: Widgets are auto-registered in Factory, so after
# declaring the Widget subclass, we can resolve it.
# (Kivy properties ("text" here) can be set at instantiation)
wow.add_widget(Factory.Magic(text='not a Rabbit'))

# WOW 9: The Rabbit class can be instantiated now, because the
# base class name "Magic" is resolvable by Factory. Since the
# Rabbit class is declared in kvlang (known as a "dynamic class"),
# this is the only way you can reach it outside kvlang.
wow.add_widget(Factory.Rabbit())

# You can use both Rabbit and Magic is kvlang. This is a
# layer of indirection on top of Factory.Rabbit().
wow.add_widget(Builder.load_string('Rabbit:'))

# WOW 10: You can mess around with factory too, if you want
# to get real fancy (as in, hacky).  This is NOT endorsed,
# but it is sometimes practical..
Factory.unregister('Label') # (NOT ENDORSED)
Factory.register('Label', cls=Factory.Rabbit) # (NOT ENDORSED)
wow.add_widget(Builder.load_string('Label:')) # now a Rabbit

runTouchApp(wow)