Widget observer framework

pyface/i_widget.py

@@ -12,6 +12,7 @@
 
 
 from traits.api import Any, Bool, HasTraits, Interface
+from traits.trait_base import not_none
 
 
 class IWidget(Interface):
@@ -90,11 +91,21 @@ def _remove_event_listeners(self):
         """ Remove toolkit-specific bindings for events """
 
 
-class MWidget(object):
+class MWidget(HasTraits):
     """ The mixin class that contains common code for toolkit specific
     implementations of the IWidget interface.
     """
 
+    def destroy(self):
+        """ Destroy the control if it exists.
+
+        Subclasses of this mixin should ensure that they call super()
+        if they override this method.
+        """
+        if self.control is not None:
+            self._remove_event_listeners()
+            self.control = None
+
     # ------------------------------------------------------------------------
     # Protected 'IWidget' interface.
     # ------------------------------------------------------------------------
@@ -104,13 +115,18 @@ def _create(self):
 
         This method should create the control and assign it to the
         :py:attr:``control`` trait.
+
+        Subclasses of this mixin should ensure that they call super()
+        if they override this method.
         """
         self.control = self._create_control(self.parent)
         self._add_event_listeners()
 
     def _create_control(self, parent):
         """ Create toolkit specific control that represents the widget.
 
+        Subclasses of this mixin should implement this method.
+
         Parameters
         ----------
         parent : toolkit control
@@ -125,9 +141,29 @@ def _create_control(self, parent):
         raise NotImplementedError()
 
     def _add_event_listeners(self):
-        """ Set up toolkit-specific bindings for events """
-        pass
+        """ Set up toolkit-specific bindings for events and trait observers
+
+        The default implementation sets up observers for all traits with
+        the `widget_observer` metadata.
+
+        Subclasses should override with additional listeners, but must call
+        super() to ensure superclass listeners are also connected.
+        """
+        for name, trait in self.traits(widget_observer=not_none).items():
+            observer = getattr(self, trait.widget_observer)
+            self.observe(observer, name, dispatch='ui')
 
     def _remove_event_listeners(self):
-        """ Remove toolkit-specific bindings for events """
-        pass
+        """ Remove toolkit-specific bindings for events and trait observers
+
+        The default implementation removes up observers for all traits with
+        the `widget_observer` metadata.
+
+        Subclasses should override with additional listeners, but must call
+        super() to ensure superclass listeners are also removed.
+        """
+        for name, trait in self.traits(widget_observer=not_none).items():
+            observer = trait.widget_observer
+            if isinstance(observer, str):
+                observer = getattr(self, observer)
+            self.observe(observer, name, dispatch='ui', remove=True)

pyface/tests/test_widget.py

@@ -11,8 +11,10 @@
 
 import unittest
 
+from traits.api import Any, Bool
 from traits.testing.unittest_tools import UnittestTools
 
+from ..application_window import ApplicationWindow
 from ..toolkit import toolkit_object
 from ..widget import Widget
 
@@ -21,6 +23,10 @@
 
 
 class ConcreteWidget(Widget):
+
+    # a trait for testing connection of observeres
+    flag = Bool(widget_observer='_flag_updated')
+
     def _create_control(self, parent):
         if toolkit_object.toolkit == "wx":
             import wx
@@ -38,6 +44,9 @@ def _create_control(self, parent):
             control = None
         return control
 
+    def _flag_updated(self, event):
+        self.flag_event = event
+
 
 class TestWidget(unittest.TestCase, UnittestTools):
     def setUp(self):
@@ -83,6 +92,36 @@ def test_enabled(self):
 
         self.assertFalse(self.widget.enabled)
 
+    def test_widget_observers(self):
+        self.window = ApplicationWindow()
+        self.window._create()
+
+        self.widget = ConcreteWidget(parent=self.window.control)
+        self.widget._create()
+
+        try:
+            with self.assertTraitChanges(self.widget, "flag", count=1):
+                self.widget.flag = True
+
+            flag_event = getattr(self.widget, 'flag_event', None)
+            self.assertIsNotNone(flag_event)
+            self.assertEqual(flag_event.object, self.widget)
+            self.assertEqual(flag_event.name, "flag")
+            self.assertEqual(flag_event.old, False)
+            self.assertEqual(flag_event.new, True)
+
+            self.widget.flag_event = None
+
+            self.widget.destroy()
+
+            with self.assertTraitChanges(self.widget, "flag", count=1):
+                self.widget.flag = False
+
+            self.assertIsNone(self.widget.flag_event)
+
+        finally:
+            self.window.destroy()
+
 
 @unittest.skipIf(no_gui_test_assistant, "No GuiTestAssistant")
 class TestConcreteWidget(unittest.TestCase, GuiTestAssistant):

pyface/ui/qt4/widget.py

@@ -73,20 +73,21 @@ def enable(self, enabled):
             self.control.setEnabled(enabled)
 
     def destroy(self):
-        self._remove_event_listeners()
         if self.control is not None:
             self.control.hide()
             self.control.deleteLater()
-            self.control = None
+        super().destroy()
 
     def _add_event_listeners(self):
+        super()._add_event_listeners()
         self.control.installEventFilter(self._event_filter)
 
     def _remove_event_listeners(self):
         if self._event_filter is not None:
             if self.control is not None:
                 self.control.removeEventFilter(self._event_filter)
             self._event_filter = None
+        super()._remove_event_listeners()
 
     # Trait change handlers --------------------------------------------------
 

pyface/ui/wx/widget.py

@@ -70,4 +70,4 @@ def enable(self, enabled):
     def destroy(self):
         if self.control is not None:
             self.control.Destroy()
-            self.control = None
+        super().destroy()