title: Adding Scrollbar to Boxlayout in Kivy
body: <p>I am trying to a Boxlayout with ScrollBar in Kivy, but I am not able to do it.  Below excerpt of .kv file.  I am dynamically adding controls to Boxlayout once the Boxlayout overflows controls are hidden and there is not Scrollbar.  Please advise.</p>
  
  <pre><code>&lt;ProcessorUI&gt;: #GridLayout
      cols: 1
      rows: 3
      Label:
          text: 'Output'
          size_hint_x: None
          width: 100
          size_hint_y: None
          height: 20
      ScrollView:
          size_hint: (None, None)
          size: (400, 400)
          BoxLayout:
              id: output
              orientation: 'vertical'
      GridLayout
          cols: 2
          TextInput:
              id: input
              multiline: True
              size_hint_y: None
              height: 40
          Button:
              id: btn_process
              text: 'Process'
              size_hint_x: None
              width: 100
              size_hint_y: None
              height: 40
              on_press: root.on_event()
  </code></pre>