demo.kv

#:kivy 1.9

# In Kivy language, the widget added last is at the top of the window in terms of Z.
# So to make sure that buttons receive the click event, add them last so they are not
# overridden by the other widgets.

<StartScreen>:
	entire_window: entire_window
	nav_bar: nav_bar
	action_group: action_group

	BoxLayout:
		id: entire_window
		size_hint: 1, 1
		orientation: "vertical"

		ActionBar:
			id: nav_bar
			pos_hint: { "top": 1 }
			ActionView:
				use_separator: False
				ActionPrevious:
					title: "Demo App"
					with_previous: False
				ActionButton:
					text: "New"
					on_release: root.add_button( )
				ActionGroup:
					id: action_group
					text: "Group 1"
					mode: "spinner"
				ActionGroup:
					text: "Group 2"
					mode: "spinner"
					ActionButton:
						font_size: 14
						text: "Button 1"
					ActionButton:
						font_size: 14
						text: "Button 2"

		BoxLayout:
			size: root.size
			pos: root.pos
			orientation: "vertical"

			canvas.before:
				Color:
					rgba: 0.2, 0.2, 0.2, 1
				Rectangle:
					pos: self.pos
					size: self.size

main.py

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.gridlayout import GridLayout
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button
from kivy.properties import ObjectProperty, ListProperty, NumericProperty, StringProperty
from kivy.uix.actionbar import ActionButton

class StartScreen( Screen ):

	def add_button( self ):
		print( "clicked" )

		btn = ActionButton( text = "New button" )
		self.action_group._dropdown.add_widget( btn )
		self.action_group._dropdown.height += btn.height

class DemoApp(App):

	def build(self):
		sm = ScreenManager()
		self.sm = sm
		sm.add_widget( StartScreen( name = "start" ) )
		return sm

root = None

if __name__ == '__main__':
	root = DemoApp( )
	root.run()