title: Clear widget kivy
body: <p>I am newbie of kivy.
  I have a button to refresh list items from database,
  This is function bound to that button:</p>
  
  <pre><code>def refresh_account(self):
      self.ids.grid.clear_widgets()
      for d in self.listdata:
          self.acc_grid.add_row(d, body_alignment, col_size)
      scroll = ScrollView(size_hint=(0.9, 0.9), size=(400, 50000), scroll_y=0, pos=(40, -30))
      scroll.clear_widgets()
      print "scroll children : ", scroll.children
      scroll.add_widget(self.acc_grid)
      scroll.do_scroll_y = True
      scroll.do_scroll_x = False
      self.ids.grid.add_widget(self.scroll)
  </code></pre>
  
  <p>I recieve an error : </p>
  
  <blockquote>
    <p>kivy.uix.widget.WidgetException: Cannot add "grid.DataGrid object at
    0x7fd415756ce8", it already has a parent
    "kivy.uix.scrollview.ScrollView object at 0x7fd413771b48"</p>
  </blockquote>
  
  <p>Any reason for this? I have removed all widget by <code>scroll.clear_widgets()</code> and scroll children print out is "[]" ?</p>