popup: fixed popup usage when content is defined from kv + add example. closes #562

examples/widgets/popup_with_kv.py

@@ -0,0 +1,33 @@
+'''
+Example to show a Popup usage with the content from kv lang.
+'''
+from kivy.uix.popup import Popup
+from kivy.uix.button import Button
+from kivy.app import App
+from kivy.lang import Builder
+
+Builder.load_string('''
+<CustomPopup>:
+    size_hint: .5, .5
+    auto_dismiss: False
+    title: 'Hello world'
+    Button:
+        text: 'Click me to dismiss'
+        on_press: root.dismiss()
+
+''')
+
+class CustomPopup(Popup):
+    pass
+
+class TestApp(App):
+    def build(self):
+        b = Button()
+        b.bind(on_press=self.show_popup)
+        return b
+
+    def show_popup(self, b):
+        p = CustomPopup()
+        p.open()
+
+TestApp().run()

kivy/uix/popup.py

@@ -65,6 +65,7 @@ popup from closing by explictly returning True from your callback ::
 
 '''
 
+__all__ = ('Popup', 'PopupException')
 
 from kivy.logger import Logger
 from kivy.animation import Animation
@@ -73,6 +74,13 @@ from kivy.properties import StringProperty, BooleanProperty, ObjectProperty, \
     NumericProperty, ListProperty
 
 
+class PopupException(Exception):
+    '''Popup exception, fired when multiple content are added to the popup.
+
+    .. versionadded:: 1.4.0
+    '''
+
+
 class Popup(FloatLayout):
     '''Popup class. See module documentation for more information.
 
@@ -194,6 +202,14 @@ class Popup(FloatLayout):
             window = Window
         return window
 
+    def add_widget(self, widget):
+        if self._container:
+            if self.content:
+                raise PopupException('Popup can have only one widget as content')
+            self.content = widget
+        else:
+            super(Popup, self).add_widget(widget)
+
     def open(self, *largs):
         '''Show the popup window from the :data:`attach_to` widget. If set, it
         will attach to the nearest window. If the widget is not attached to any