All things with an UpdatePrefs() message listen for an event...

... Still to do, improve the handling of updates of only subsets of the prefs

src/Menus.h

@@ -13,6 +13,7 @@
 #include "audacity/Types.h"
 
 #include <wx/string.h> // member variable
+#include "Prefs.h"
 
 class wxArrayString;
 class AudacityProject;
@@ -32,13 +33,6 @@ enum EffectType : int;
 typedef wxString PluginID;
 typedef wxArrayString PluginIDs;
 
-class PrefsListener
-{
-public:
-   virtual ~PrefsListener();
-   virtual void UpdatePrefs(); // default is no-op
-};
-
 class MenuCreator
 {
 public:
@@ -56,9 +50,11 @@ public:
    PluginID mLastEffect{};
 };
 
-class MenuManager : public MenuCreator
+class MenuManager final : public MenuCreator, private PrefsListener
 {
 public:
+   MenuManager();
+
    static void ModifyUndoMenuItems(AudacityProject &project);
    static void ModifyToolbarMenus(AudacityProject &project);
    // Calls ModifyToolbarMenus() on all projects
@@ -72,7 +68,7 @@ public:
    // inactive project as it is needlessly expensive.
    CommandFlag GetUpdateFlags(
       AudacityProject &project, bool checkActive = false);
-   void UpdatePrefs();
+   void UpdatePrefs() override;
 
    // Command Handling
    bool ReportIfActionNotAllowed(