Implement the AboutToShow callbacks

src/calibre/gui2/dbus_export/demo.py

@@ -28,7 +28,8 @@ class MainWindow(QMainWindow):
         self.l = QVBoxLayout(w)
         mb = f.create_window_menubar(self)
         self.setMenuBar(mb)
-        m = mb.addMenu('&One')
+        m = self.menu_one = mb.addMenu('&One')
+        m.aboutToShow.connect(self.about_to_show_one)
         s = self.style()
         for i, icon in zip(xrange(3), map(s.standardIcon, (s.SP_DialogOkButton, s.SP_DialogCancelButton, s.SP_ArrowUp))):
             ac = m.addAction('One - &%d' % (i + 1))
@@ -41,6 +42,9 @@ class MainWindow(QMainWindow):
         g = QActionGroup(self)
         make_checkable(g.addAction(m.addAction('Exclusive 1')))
         make_checkable(g.addAction(m.addAction('Exclusive 2')), False)
+        m.addSeparator()
+        self.about_to_show_sentinel = m.addAction('This action\'s text should change before menu is shown')
+        self.as_count = 0
         for ac in mb.findChildren(QAction):
             ac.triggered.connect(self.action_triggered)
 
@@ -49,6 +53,10 @@ class MainWindow(QMainWindow):
         text = 'Action triggered: %s' % ac.text()
         self.statusBar().showMessage(text)
 
+    def about_to_show_one(self):
+        self.as_count += 1
+        self.about_to_show_sentinel.setText('About to show handled: %d' % self.as_count)
+
 app = QApplication([])
 f = factory()
 mw = MainWindow()

src/calibre/gui2/dbus_export/menu.py

@@ -228,6 +228,15 @@ class DBusMenu(QObject):
                 ac.toggle()
             ac.triggered.emit(ac.isCheckable() and ac.isChecked())
 
+    def handle_about_to_show(self, ac):
+        child_ids = {self.action_to_id(x) for x in ac.menu().actions()}
+        child_ids.discard(None)
+        ac_id = self.action_to_id(ac)
+        ac.menu().aboutToShow.emit()
+        if ac_id in self.layout_changes or child_ids.intersection(self.action_changes):
+            return True
+        return False
+
 class DBusMenuAPI(Object):
 
     IFACE = 'com.canonical.dbusmenu'
@@ -302,11 +311,23 @@ class DBusMenuAPI(Object):
 
     @dbus_method(IFACE, in_signature='i', out_signature='b')
     def AboutToShow(self, id):
-        pass
+        ac = self.menu.id_to_action(id)
+        if ac is not None and ac.menu() is not None:
+            return self.menu.handle_about_to_show(ac)
+        return False
 
     @dbus_method(IFACE, in_signature='ai', out_signature='aiai')
     def AboutToShowGroup(self, ids):
-        pass
+        updates_needed = dbus.Array(signature='i')
+        id_errors = dbus.Array(signature='i')
+        for ac_id in ids:
+            ac = self.menu.id_to_action(id)
+            if ac is not None and ac.menu() is not None:
+                if self.menu.handle_about_to_show(ac):
+                    updates_needed.append(ac_id)
+            else:
+                id_errors.append(ac_id)
+        return updates_needed, id_errors
 
     @dbus_signal(IFACE, 'a(ia{sv})a(ias)')
     def ItemsPropertiesUpdated(self, updatedProps, removedProps):

src/calibre/gui2/dbus_export/utils.py

@@ -14,7 +14,7 @@ from PyQt5.Qt import QSize, QImage, Qt, QKeySequence, QBuffer, QByteArray
 
 def log(*args, **kw):
     kw['file'] = sys.stderr
-    print('StatusNotifier:', *args, **kw)
+    print('DBusExport:', *args, **kw)
     kw['file'].flush()
 
 

src/calibre/gui2/dbus_export/widgets.py

@@ -6,12 +6,17 @@ from __future__ import (unicode_literals, division, absolute_import,
 __license__ = 'GPL v3'
 __copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
 
-import time
+import time, sys
 
 from PyQt5.Qt import QObject, QMenuBar, QAction, QEvent
 
 UNITY_WINDOW_REGISTRAR = ('com.canonical.AppMenu.Registrar', '/com/canonical/AppMenu/Registrar', 'com.canonical.AppMenu.Registrar')
 
+def log(*args, **kw):
+    kw['file'] = sys.stderr
+    print('DBusExport:', *args, **kw)
+    kw['file'].flush()
+
 class MenuBarAction(QAction):
 
     def __init__(self, mb):
@@ -92,7 +97,7 @@ class Factory(QObject):
                 self._bus = self.dbus.SessionBus()
                 self._bus.call_on_disconnection(self.bus_disconnected)
             except Exception as err:
-                print ('Failed to connect to DBUS session bus, with error:', str(err))
+                log('Failed to connect to DBUS session bus, with error:', str(err))
                 self._bus = False
         return self._bus or None
 
@@ -106,7 +111,7 @@ class Factory(QObject):
                     self.detect_menu_registrar()
                 except Exception as err:
                     self.menu_registrar = False
-                    print ('Failed to detect window menu registrar, with error:', str(err))
+                    log('Failed to detect window menu registrar, with error:', str(err))
         return bool(self.menu_registrar)
 
     def detect_menu_registrar(self):