title: get values from a different screen (kivy)
body: <p>I´m trying to achieve the following: capture the text from from Label: id: fb in screen FolderB and copy/add to Label: id: fa in screen FolderA by pressing the Button "get the txt from Folder B". Please find the codes below:
  Thanks in advance,</p>
  
  <h1>file main.py</h1>
  
  <pre><code>from kivy.app import App
  from kivy.uix.screenmanager import ScreenManager, Screen
  from kivy.lang import Builder
  
  Builder.load_file('foldera.kv')
  Builder.load_file('folderb.kv')
  
  class MainScreen(ScreenManager):
      pass
  
  class FolderA(Screen):
      pass
  
  class FolderB(Screen):
      pass
  
  class FTest(App):
      def build(self):
          return MainScreen()
  
  
  if __name__ == '__main__':
      FTest().run()
  </code></pre>
  
  <h1>file ftest.kv (class build)</h1>
  
  <pre><code>&lt;FolderA@FolderA&gt;
  &lt;FolderB@FolderB&gt;
  
  &lt;MainScreen&gt;:
      FolderA:
          name: 'foldera'
      FolderB:
          name: 'folderb'
  </code></pre>
  
  <h1>file foldera.kv (boxlayout)</h1>
  
  <pre><code>&lt;FolderA&gt;:
      BoxLayout:
          orientation: 'vertical'
          Label:
              text: 'Folder A'
          Button:
              text: 'go to Folder B'
              on_press: app.root.current = 'folderb'
          Label:
              id: fa
              text: ''
          Button:
              text: 'get text from Folder B'
              on_press: "this is the button where i'm trying to apply the action"
  </code></pre>
  
  <h1>file folderb.kv (boxlayout)</h1>
  
  <pre><code>&lt;FolderB&gt;:
      BoxLayout:
          orientation: 'vertical'
          Label:
              text: 'Folder B'
          Button:
              text: 'go to Folder B'
              on_press: app.root.current = 'foldera'
          Label:
              id: fb
              text: 'TEXT: CAPTURE THIS TEXT'
  </code></pre>
  
  <h1>screenshot</h1>
  
  <p><a href="https://i.stack.imgur.com/0m36K.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0m36K.jpg" alt="Img01"></a>
  <a href="https://i.stack.imgur.com/Mk9do.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Mk9do.jpg" alt="Img02"></a></p>