title: Interaction between Kivy widgets in Python
body: <p>I'm doing a proyect using kivy but i have a problem with the checkboxes. At first I'm trying to do the program like python coding (I know it is'nt clean, but I understand more) And i have a first screen with this coding:</p>
  
  <pre><code>from kivy.app import App
  from kivy.uix.label import Label
  from kivy.uix.gridlayout import GridLayout
  from kivy.uix.floatlayout import FloatLayout
  from kivy.uix.textinput import TextInput
  from kivy.uix.button import Button
  from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
  from kivy.uix.checkbox import CheckBox
  
  
  
  
  class MainScreen(GridLayout):
      def __init__(self,**kwargs):
          e=[]
          super(MainScreen, self).__init__(**kwargs)
          self.cols=2
          def on_checkbox_active(checkbox, value):
              if value:
                  e.append(value)
                  print e
              else:
                  print('The checkbox', checkbox, 'is inactive')
  
          self.add_widget(Label(text='Inserta assignatures desitjades',font_size=35))
          self.add_widget(Label(text=''))
          ch1 = CheckBox()
          self.add_widget(ch1)
          self.add_widget(Label(text='Termotecnia'))
          ch2 = CheckBox()
          self.add_widget(ch2)
          self.add_widget(Label(text='Termotecnia'))
          ch3 = CheckBox()
          self.add_widget(ch3)
          self.add_widget(Label(text='Termotecnia'))
          ch4 = CheckBox()
          self.add_widget(ch4)
          self.add_widget(Label(text='Termotecnia'))
          b1=Button(text='Exit',background_color=[0.7,0.7,1,1],font_size=24)  
          self.add_widget(b1)
          b2=Button(text='Next',font_size=24,font_color=[1,3,4,0],background_color=[1,2,3,6]) 
          self.add_widget(b2)
          ch1.bind(active=on_checkbox_active)
          ch2.bind(active=on_checkbox_active)
          b1.bind(on_press=exit)
          b2.bind(on_press=reloaded)
  ...
  
  class SimpleKivy(App):
      def build(self):
          return MainScreen()
  
  
  if __name__=='__main__':
      SimpleKivy().run()
  </code></pre>
  
  <p>I want to select two or three options for example, and save it for the next screen, like a type of selection. If anyone knows how to do it and save information for the next screen it woul help me a lot, because i have the code of the next screen for all the options, but i want to preselect in the first screen and then only use which i have selected. Also if anyone can help me, i want to know hoy to do the transition to another class (screen) when the button "Next" is pressed. I know this question are pretty simple but I'm new in kivy programming and some concepts are pretty difficult. Thanks. </p>