FIX: properly destroy tasks actions

A few tasks-related actions did not properly dispose
of listeners to other object when they were destroyed.

pyface/tasks/action/dock_pane_toggle_group.py

@@ -1,13 +1,13 @@
 # Enthought library imports.
 from pyface.action.api import Action, ActionItem, Group
-from traits.api import Bool, Instance, List, Property, Unicode, on_trait_change
+from traits.api import Instance, List, Property, Unicode, on_trait_change
 
 # Local imports.
 from pyface.tasks.i_dock_pane import IDockPane
 
 
 class DockPaneToggleAction(Action):
-    """ An Action for toggling the visibily of a dock pane.
+    """ An Action for toggling the visibility of a dock pane.
     """
 
     #### 'DockPaneToggleAction' interface #####################################
@@ -24,6 +24,14 @@ class DockPaneToggleAction(Action):
     # 'Action' interface.
     ###########################################################################
 
+    def destroy(self):
+        super(DockPaneToggleAction, self).destroy()
+
+        # Make sure that we are not listening to changes to the pane anymore.
+        # In traits style, we will set the basic object to None and have the
+        # listener check that if it is still there.
+        self.dock_pane = None
+
     def perform(self, event=None):
         if self.dock_pane:
             self.dock_pane.visible = not self.dock_pane.visible
@@ -33,18 +41,22 @@ def perform(self, event=None):
     ###########################################################################
 
     def _get_name(self):
+        if self.dock_pane is None:
+            return 'DELETED DOCK TOGGLE'
         return self.dock_pane.name
 
     def _get_tooltip(self):
-        return u'Toggles the visibilty of the %s pane.' % self.name
+        return u'Toggles the visibility of the %s pane.' % self.name
 
     @on_trait_change('dock_pane.visible')
     def _update_checked(self):
-        self.checked = self.dock_pane.visible
+        if self.dock_pane:
+            self.checked = self.dock_pane.visible
 
     @on_trait_change('dock_pane.closable')
     def _update_visible(self):
-        self.visible = self.dock_pane.closable
+        if self.dock_pane:
+            self.visible = self.dock_pane.closable
 
 
 class DockPaneToggleGroup(Group):

pyface/tasks/action/listening_action.py

@@ -34,6 +34,21 @@ class ListeningAction(Action):
     # 'Action' interface.
     ###########################################################################
 
+    def destroy(self):
+        """ Called when the action is no longer required.
+
+        Remove all the task listeners.
+
+        """
+
+        if self.object:
+            self.object.on_trait_change(
+                self._enabled_update, self.enabled_name, remove=True
+            )
+            self.object.on_trait_change(
+                self._visible_update, self.visible_name, remove=True
+            )
+
     def perform(self, event=None):
         """ Call the appropriate function.
         """

pyface/tasks/action/task_toggle_group.py

@@ -1,7 +1,6 @@
 # Enthought library imports.
 from pyface.action.api import Action, ActionItem, Group
-from traits.api import Any, Bool, List, Instance, Property, Unicode, \
-    on_trait_change
+from traits.api import Any, List, Instance, Property, Unicode, on_trait_change
 
 # Local imports.
 from pyface.tasks.task import Task
@@ -26,6 +25,14 @@ class TaskToggleAction(Action):
     # 'Action' interface.
     ###########################################################################
 
+    def destroy(self):
+        super(TaskToggleAction, self).destroy()
+
+        # Make sure that we are not listening to changes in the task anymore
+        # In traits style, we will set the basic object to None and have the
+        # listener check that if it is still there.
+        self.task = None
+
     def perform(self, event=None):
         window = self.task.window
         window.activate_task(self.task)
@@ -35,15 +42,19 @@ def perform(self, event=None):
     ###########################################################################
 
     def _get_name(self):
+        if self.task is None:
+            return 'DELETED TASK TOGGLE'
         return self.task.name
 
     def _get_tooltip(self):
         return u'Switch to the %s task.' % self.name
 
     @on_trait_change('task.window.active_task')
     def _update_checked(self):
-        window = self.task.window
-        self.checked = window is not None and window.active_task == self.task
+        if self.task:
+            window = self.task.window
+            self.checked = (window is not None
+                            and window.active_task == self.task)
 
 
 class TaskToggleGroup(Group):