title: Delay a countdown clock until I change screens
body: <p>I am trying to make a simple memory game with a countdown at the beginning of every game. The app will begin with a begin memory test button that will take you to the first game. When the game screen comes on I want to begin the countdown from 10 seconds before it begins. Currently when I open the app the countdown begins before I change screens. The current game screen is called settings screen.</p>
  
  <p>main.py</p>
  
  <pre><code>class HomeScreen(Screen):
      pass
  
  class GameScreen(Screen):
      pass
  
  class SettingsScreen(Screen):
      pass
  
  class ImageButton(ButtonBehavior, Image):
      pass
  
  GUI = Builder.load_file("main.kv")
  
  class MainApp(App):
      def build(self):
          return GUI
  
      def change_screen(self, screen_name):
          #get the screen manager from the kv file
          screen_manager = self.root.ids['screen_manager']
          screen_manager.current = screen_name
  
      def on_start(settings_screen):
          settings_screen.function_interval = Clock.schedule_interval(settings_screen.update_label, 1)
          Clock.schedule_once(settings_screen.stop_interval, 10)
      def stop_interval(settings_screen, *args):
          settings_screen.function_interval.cancel()
      def update_label(settings_screen, *args):
          settings_screen.root.ids.counter.text = str(int(settings_screen.root.ids.counter.text) - 1)
  
  MainApp().run()
  </code></pre>
  
  <p>main.kv</p>
  
  <pre><code>#:include kv/homescreen.kv
  #:include kv/settingsscreen.kv
  
  GridLayout:
      cols: 1
      ScreenManager:
          id: screen_manager
          HomeScreen:
              name: "home_screen"
              id: home_screen
          SettingsScreen:
              name: "settings_screen"
              id: settings_screen
              Label:
                  id: counter
                  text:"10"
          GameScreen:
              name: "game_screen"
              id: game_screen
  </code></pre>
  
  <p>settingsscreen.kv</p>
  
  <pre><code>&lt;SettingsScreen&gt;:
      GridLayout:
          canvas:
              Color:
                  rgb: utils.get_color_from_hex("#39B3F2")
              Rectangle:
                  size: self.size
                  pos: self.pos
          rows: 2
          ImageButton:
              source: "kv\\icons\\red1.png"
              on_release:
                  print("selected red button")
          ImageButton:
              source: "kv\\icons\\yellow1.png"
              on_release:
                  print("selected yellow button")
          ImageButton:
              source: "kv\\icons\\yellow2.png"
              on_release:
                  print("selected yellow button")
          ImageButton:
              source: "kv\\icons\\red2.png"
              on_release:
                  print("selected red button")
  </code></pre>