python - How to pass properties from one class to another in kivy -

in application, have multiple screens. each screen corresponds class. display property calculated in class (screen) on screen. below simplified example outline problem. in class wordcomprehension, numericproperty count_r incremented, every time button pressed. now, display result of calculation in scorescreen. suggestions. here .py:

import kivy kivy.app import app  kivy.uix.boxlayout import boxlayout kivy.uix.floatlayout import floatlayout kivy.uix.label import label kivy.uix.button import button  kivy.properties import objectproperty kivy.properties import numericproperty   class appscreen(floatlayout):     app = objectproperty(none)  class mainmenu(appscreen):     pass  class scorescreen(appscreen):      score = numericproperty(0)     def get_score(self):         wordcomp = wordcomprehension()         self.score = wordcomp.count_r   class wordcomprehension(appscreen):     count_r = numericproperty(0)     count_w = numericproperty(0)      def do_something(self):         self.count_r += 1   class interfaceapp(app):     def build(self):         self.screens = {}         self.screens["wordcomp"] = wordcomprehension(app=self)         self.screens["menu"] = mainmenu(app=self)         self.screens["score"] = scorescreen(app=self)         self.root = floatlayout()         self.goto_screen("menu")         return self.root      def goto_screen(self, screen_name):         self.root.clear_widgets()         self.root.add_widget(self.screens[screen_name])   if __name__ == "__main__":     interfaceapp().run() 

and .kv:

#:kivy 1.8.0  <mainmenu>:     boxlayout:         orientation: 'vertical'         label:             text: "choose category"             font_size: 30          button:             text: 'word comprehension'             on_press: root.app.goto_screen("wordcomp")         button:             text: 'highscore'             on_press: root.app.goto_screen("score")             disabled: false  <scorescreen>:     boxlayout:         orientation: 'vertical'         button:             text: 'get score'             on_press: root.get_score()         label:             text: "word comprehension right answers:" + str(root.score)         button:             text: 'main menu'             on_release: root.app.goto_screen("menu")   <wordcomprehension>:     boxlayout:         orientation: 'vertical'         label:             text: str(root.count_r)         button:             text: 'do something'             on_release: root.do_something()         button:             text: 'menu'             on_press: root.app.goto_screen("menu") 

you can bind kivy properties 1 another, when 1 changes other. bind setter() function of class. (http://kivy.org/docs/api-kivy.event.html)

here need do:

1) create numericproperty in scorescreen count_r. 2) bind count_r numericproperty in wordcomprehension numericproperty in scorescreen : '''in class wordcomprehension ''' self.bind(count_r=self.score_screen.setter('count_r')

now trick need have reference scorescreen instance in wordcomprehension class. in example, assumed have reference in self.score_screen. leave how want assign reference.

now whenever count_r changed in wordcomprehension, setter function (which setattr() ) gets called on 'count_r' property of scorescreen.

another thing: line wordcomp = wordcomprehension() in get_score() not referencing same wordcomprehension instance want. creating new object of class wordcomprehension , referencing it's count_r it's default value.

edit1 not sure if want code make score property update whenever count_r property changed:

import kivy kivy.app import app  kivy.uix.boxlayout import boxlayout kivy.uix.floatlayout import floatlayout kivy.uix.label import label kivy.uix.button import button  kivy.properties import objectproperty kivy.properties import numericproperty   class appscreen(floatlayout):     app = objectproperty(none)  class mainmenu(appscreen):     pass  class scorescreen(appscreen):     count_r = numericproperty(0)     score = numericproperty(0)      # making new wordcomprehension object, , not have     # correct value of score. no longer need binding properties     # together.     #def get_score(self):     #    wordcomp = wordcomprehension()     #    self.score = wordcomp.count_r   class wordcomprehension(appscreen):     count_r = numericproperty(0)     count_w = numericproperty(0)      def do_something(self):         self.count_r += 1   class interfaceapp(app):     def build(self):         self.screens = {}         self.screens["wordcomp"] = wordcomprehension(app=self)         self.screens["menu"] = mainmenu(app=self)         self.screens["score"] = scorescreen(app=self)         self.root = floatlayout()         self.goto_screen("menu")          # bind 2 properties together. whenever count_r changes in wordcomp         # screen, score property in score screen reflect changes.         self.screens["wordcomp"].bind(count_r=self.screens["score"].setter('score'))          return self.root      def goto_screen(self, screen_name):         self.root.clear_widgets()         self.root.add_widget(self.screens[screen_name])   if __name__ == "__main__":     interfaceapp().run()