Merge pull request #585 from kivy/add__widget

UIX: Widget: Raise Exception if widget already has parent.

kivy/uix/bubble.py

@@ -157,6 +157,7 @@ def __init__(self, **kwargs):
             color=self.background_color)
         self.content = content = BubbleContent(parent=self)
         super(Bubble, self).__init__(**kwargs)
+        content.parent = None
         self.add_widget(content)
         self.on_arrow_pos()
 
@@ -226,6 +227,10 @@ def on_arrow_pos(self, *l):
         self_arrow_img.height = self_arrow_img.texture_size[1]
         widget_list = []
         arrow_list = []
+        parent = self_arrow_img.parent
+        if parent:
+            parent.remove_widget(self_arrow_img)
+
         if self_arrow_pos[0] == 'b' or self_arrow_pos[0] == 't':
             self.cols = 1
             self.rows = 2

kivy/uix/tabbedpanel.py

@@ -393,6 +393,9 @@ def add_widget(self, widget, index=0):
         content = self.content
         if content is None:
             return
+        parent = widget.parent
+        if widget.parent:
+            parent.remove_widget(widget)
         if widget == content or widget == self._tab_layout:
             super(TabbedPanel, self).add_widget(widget, index)
         elif isinstance(widget, TabbedPanelHeader):
@@ -491,6 +494,9 @@ def on_tab_pos(self, *l):
         tab_layout.clear_widgets()
         scrl_v = ScrollView(size_hint=(None, 1))
         tabs = self._tab_strip
+        parent = tabs.parent
+        if parent:
+            parent.remove_widget(tabs)
         scrl_v.add_widget(tabs)
         scrl_v.pos = (0, 0)
         self_update_scrollview = self._update_scrollview

kivy/uix/widget.py

@@ -226,6 +226,11 @@ def add_widget(self, widget, index=0):
         if not isinstance(widget, Widget):
             raise WidgetException(
                 'add_widget() can be used only with Widget classes.')
+        parent = widget.parent
+        # check if widget is already a child of another widget
+        if parent:
+            raise WidgetException('Cannot add %r, it already has a parent %r'
+                % (widget, parent))
         widget.parent = self
         if index == 0 or len(self.children) == 0:
             self.children.insert(0, widget)