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/AdornedRulerPanel.cpp

@@ -893,6 +893,9 @@ AdornedRulerPanel::AdornedRulerPanel(AudacityProject* project,
    wxTheApp->Bind(EVT_AUDIOIO_CAPTURE,
                      &AdornedRulerPanel::OnRecordStartStop,
                      this);
+
+   // Delay until after CommandManager has been populated:
+   this->CallAfter( &AdornedRulerPanel::UpdatePrefs );
 }
 
 AdornedRulerPanel::~AdornedRulerPanel()
@@ -1797,8 +1800,11 @@ void AdornedRulerPanel::OnAutoScroll(wxCommandEvent&)
       gPrefs->Write(wxT("/GUI/AutoScroll"), false);
    else
       gPrefs->Write(wxT("/GUI/AutoScroll"), true);
-   mProject->UpdatePrefs();
+
    gPrefs->Flush();
+
+   wxTheApp->AddPendingEvent(wxCommandEvent{
+      EVT_PREFS_UPDATE, ViewInfo::UpdateScrollPrefsID() });
 }
 
 

src/AdornedRulerPanel.h

@@ -13,6 +13,7 @@
 
 #include "CellularPanel.h"
 #include "widgets/Ruler.h" // member variable
+#include "Prefs.h"
 
 class ViewInfo;
 class AudacityProject;
@@ -20,7 +21,9 @@ class SnapManager;
 class TrackList;
 
 // This is an Audacity Specific ruler panel.
-class AUDACITY_DLL_API AdornedRulerPanel final : public CellularPanel
+class AUDACITY_DLL_API AdornedRulerPanel final
+: public CellularPanel
+, private PrefsListener
 {
 public:
    AdornedRulerPanel(AudacityProject *project,
@@ -53,7 +56,7 @@ public:
 
    void InvalidateRuler();
 
-   void UpdatePrefs();
+   void UpdatePrefs() override;
    void ReCreateButtons();
 
    void RegenerateTooltips();

src/Menus.cpp

@@ -51,14 +51,6 @@
 
 #include <wx/menu.h>
 
-PrefsListener::~PrefsListener()
-{
-}
-
-void PrefsListener::UpdatePrefs()
-{
-}
-
 MenuManager &GetMenuManager(AudacityProject &project)
 { return *project.mMenuManager; }
 
@@ -70,6 +62,11 @@ MenuCreator::~MenuCreator()
 {
 }
 
+MenuManager::MenuManager()
+{
+   UpdatePrefs();
+}
+
 void MenuManager::UpdatePrefs()
 {
    bool bSelectAllIfNone;
@@ -388,6 +385,7 @@ CommandFlag MenuManager::GetFocusedFrame(AudacityProject &project)
    return AlwaysEnabledFlag;
 }
 
+
 CommandFlag MenuManager::GetUpdateFlags
 (AudacityProject &project, bool checkActive)
 {

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(

src/MixerBoard.cpp

@@ -356,8 +356,6 @@ void MixerTrackCluster::UpdatePrefs()
 {
    this->SetBackgroundColour( theTheme.Colour( clrMedium ) );
    mStaticText_TrackName->SetForegroundColour(theTheme.Colour(clrTrackPanelText));
-   if (mMeter)
-      mMeter->UpdatePrefs(); // in case meter range has changed
    HandleResize(); // in case prefs "/GUI/Solo" changed
 }
 #endif

src/MixerBoard.h

@@ -20,6 +20,8 @@
 #include "widgets/ASlider.h" // to inherit
 #include "commands/CommandManagerWindowClasses.h"
 
+#include "Prefs.h"
+
 class wxArrayString;
 class wxBitmapButton;
 class wxImage;
@@ -188,7 +190,7 @@ public:
 class MixerBoardFrame;
 class TrackList;
 
-class MixerBoard final : public wxWindow
+class MixerBoard final : public wxWindow, private PrefsListener
 {
    friend class MixerBoardFrame;
 
@@ -198,7 +200,7 @@ public:
                const wxPoint& pos = wxDefaultPosition,
                const wxSize& size = wxDefaultSize);
 
-   void UpdatePrefs();
+   void UpdatePrefs() override;
 
    // Add clusters for any tracks we're not yet showing.
    // Update pointers for tracks we're aleady showing.

src/Prefs.cpp

@@ -71,6 +71,31 @@ int gMenusDirty = 0;
 
 wxDEFINE_EVENT(EVT_PREFS_UPDATE, wxCommandEvent);
 
+PrefsListener::PrefsListener()
+{
+   wxTheApp->Bind(EVT_PREFS_UPDATE, &PrefsListener::OnEvent, this);
+}
+
+PrefsListener::~PrefsListener()
+{
+   // Explicit unbinding is needed because this is not a wxEvtHandler
+   wxTheApp->Unbind(EVT_PREFS_UPDATE, &PrefsListener::OnEvent, this);
+}
+
+void PrefsListener::UpdateSelectedPrefs( int )
+{
+}
+
+void PrefsListener::OnEvent( wxCommandEvent &evt )
+{
+   evt.Skip();
+   auto id = evt.GetId();
+   if (id <= 0)
+      UpdatePrefs();
+   else
+      UpdateSelectedPrefs( id );
+}
+
 #if 0
 // Copy one entry from one wxConfig object to another
 static void CopyEntry(wxString path, wxConfigBase *src, wxConfigBase *dst, wxString entry)

src/Prefs.h

@@ -164,4 +164,25 @@ private:
 // changes
 wxDECLARE_EVENT(EVT_PREFS_UPDATE, wxCommandEvent);
 
+// Invoke UpdatePrefs() when Preference dialog commits changes.
+class PrefsListener
+{
+public:
+   PrefsListener();
+   virtual ~PrefsListener();
+
+   // Called when all preferences should be updated.
+   virtual void UpdatePrefs() = 0;
+
+protected:
+   // Called when only selected preferences are to be updated.
+   // id is some value generated by wxNewId() that identifies the portion
+   // of preferences.
+   // Default function does nothing.
+   virtual void UpdateSelectedPrefs( int id );
+
+private:
+   void OnEvent(wxCommandEvent&);
+};
+
 #endif

src/Project.cpp

@@ -1497,7 +1497,6 @@ void AudacityProject::UpdatePrefsVariables()
 {
    gPrefs->Read(wxT("/AudioFiles/ShowId3Dialog"), &mShowId3Dialog, true);
    gPrefs->Read(wxT("/AudioFiles/NormalizeOnLoad"),&mNormalizeOnLoad, false);
-   gPrefs->Read(wxT("/GUI/AutoScroll"), &mViewInfo.bUpdateTrackIndicator, true);
    gPrefs->Read(wxT("/GUI/EmptyCanBeDirty"), &mEmptyCanBeDirty, true );
    gPrefs->Read(wxT("/GUI/ShowSplashScreen"), &mShowSplashScreen, true);
    gPrefs->Read(wxT("/GUI/Solo"), &mSoloPref, wxT("Simple"));
@@ -1531,20 +1530,6 @@ void AudacityProject::UpdatePrefs()
    UpdatePrefsVariables();
 
    SetProjectTitle();
-
-   {
-      ObjectFactorySetLocker locker;
-      for( const auto &pObject : mAttachedObjects )
-         pObject->UpdatePrefs();
-   }
-
-   GetMenuManager(*this).UpdatePrefs();
-
-   mTrackPanel->UpdatePrefs();
-   mToolManager->UpdatePrefs();
-   mRuler->UpdatePrefs();
-   if (mMixerBoard)
-      mMixerBoard->UpdatePrefs();
 }
 
 void AudacityProject::RedrawProject(const bool bForceWaveTracks /*= false*/)
@@ -3633,8 +3618,6 @@ bool AudacityProject::HandleXMLTag(const wxChar *tag, const wxChar **attrs)
             NumericConverter::LookupFormat( NumericConverter::BANDWIDTH, value ) );
    } // while
 
-   mViewInfo.UpdatePrefs();
-
    if (longVpos != 0) {
       // PRL: It seems this must happen after SetSnapTo
        mViewInfo.vpos = longVpos;
@@ -5530,10 +5513,8 @@ LyricsWindow* AudacityProject::GetLyricsWindow(bool create)
 
 MixerBoardFrame* AudacityProject::GetMixerBoardFrame(bool create)
 {
-   if (create && !mMixerBoardFrame) {
+   if (create && !mMixerBoardFrame)
       mMixerBoardFrame = safenew MixerBoardFrame{ this };
-      mMixerBoard = mMixerBoardFrame->mMixerBoard;
-   }
    return mMixerBoardFrame;
 }
 

src/Project.h

@@ -23,6 +23,7 @@
 #include "Experimental.h"
 
 #include "Track.h"
+#include "Prefs.h"
 #include "SelectionState.h"
 #include "ViewInfo.h"
 #include "commands/CommandManagerWindowClasses.h"
@@ -171,14 +172,13 @@ class WaveTrack;
 
 class MenuManager;
 
-class PrefsListener;
-
 class AUDACITY_DLL_API AudacityProject final : public wxFrame,
                                      public TrackPanelListener,
                                      public SelectionBarListener,
                                      public SpectralSelectionBarListener,
                                      public XMLTagHandler,
-                                     public AudioIOListener
+                                     public AudioIOListener,
+                                     private PrefsListener
 {
  public:
    AudacityProject(wxWindow * parent, wxWindowID id,
@@ -188,7 +188,7 @@ class AUDACITY_DLL_API AudacityProject final : public wxFrame,
    // Next available ID for sub-windows
    int NextWindowID();
 
-   using AttachedObject = PrefsListener;
+   using AttachedObject = wxObject;
    using AttachedObjectFactory =
       std::function< std::unique_ptr<AttachedObject>() >;
 
@@ -391,7 +391,7 @@ public:
    int GetProjectNumber(){ return mProjectNo;};
    static int CountUnnamed();
    static void RefreshAllTitles(bool bShowProjectNumbers );
-   void UpdatePrefs();
+   void UpdatePrefs() override;
    void UpdatePrefsVariables();
    void RedrawProject(const bool bForceWaveTracks = false);
    void RefreshCursor();
@@ -627,7 +627,6 @@ private:
    HistoryWindow *mHistoryWindow{};
    LyricsWindow* mLyricsWindow{};
    MixerBoardFrame* mMixerBoardFrame{};
-   MixerBoard* mMixerBoard{};
 
    Destroy_ptr<FreqWindow> mFreqWindow;
    Destroy_ptr<ContrastDialog> mContrastDialog;

src/TrackArtist.cpp

@@ -77,6 +77,7 @@ audio tracks.
 #include "LabelTrack.h"
 #include "TimeTrack.h"
 #include "Prefs.h"
+#include "prefs/GUIPrefs.h"
 #include "prefs/GUISettings.h"
 #include "prefs/SpectrogramSettings.h"
 #include "prefs/TracksPrefs.h"
@@ -142,7 +143,6 @@ TrackArtist::TrackArtist( TrackPanel *parent_ )
    mdBrange = ENV_DB_RANGE;
    mShowClipping = false;
    mSampleDisplay = 1;// Stem plots by default.
-   UpdatePrefs();
 
    SetColours(0);
    vruler = std::make_unique<Ruler>();
@@ -3267,15 +3267,22 @@ void TrackArt::DrawTimeTrack(TrackPanelDrawingContext &context,
         track->GetDisplayLog(), dbRange, lower, upper, false );
 }
 
+void TrackArtist::UpdateSelectedPrefs( int id )
+{
+   if( id == ShowClippingPrefsID())
+      mShowClipping = gPrefs->Read(wxT("/GUI/ShowClipping"), mShowClipping);
+}
+
 void TrackArtist::UpdatePrefs()
 {
    mdBrange = gPrefs->Read(ENV_DB_KEY, mdBrange);
-   mShowClipping = gPrefs->Read(wxT("/GUI/ShowClipping"), mShowClipping);
    mSampleDisplay = TracksPrefs::SampleViewChoice();
 
    mbShowTrackNameInTrack =
       gPrefs->ReadBool(wxT("/GUI/ShowTrackNameInWaveform"), false);
    
+   UpdateSelectedPrefs( ShowClippingPrefsID() );
+
    SetColours(0);
 }
 

src/TrackArtist.h

@@ -25,6 +25,7 @@
 #include <wx/brush.h> // member variable
 #include <wx/pen.h> // member variables
 #include "audacity/Types.h"
+#include "Prefs.h"
 
 class wxRect;
 
@@ -157,7 +158,7 @@ namespace TrackArt {
                     const wxRect & rect, int x0, int y0, int cy, bool top);
 }
 
-class AUDACITY_DLL_API TrackArtist {
+class AUDACITY_DLL_API TrackArtist final : private PrefsListener {
 
 public:
    TrackArtist( TrackPanel *parent_ );
@@ -174,7 +175,8 @@ public:
 
    void SetColours(int iColorIndex);
 
-   void UpdatePrefs();
+   void UpdatePrefs() override;
+   void UpdateSelectedPrefs( int id ) override;
 
    void UpdateVRuler(const Track *t, const wxRect & rect);
 

src/TrackPanel.cpp

@@ -273,6 +273,8 @@ TrackPanel::TrackPanel(wxWindow * parent, wxWindowID id,
    wxTheApp->Bind(EVT_AUDIOIO_PLAYBACK,
                      &TrackPanel::OnPlayback,
                      this);
+
+   UpdatePrefs();
 }
 
 
@@ -319,16 +321,8 @@ wxString TrackPanel::gSoloPref;
 
 void TrackPanel::UpdatePrefs()
 {
-   gPrefs->Read(wxT("/GUI/AutoScroll"), &mViewInfo->bUpdateTrackIndicator,
-      true);
    gPrefs->Read(wxT("/GUI/Solo"), &gSoloPref, wxT("Simple"));
 
-   mViewInfo->UpdatePrefs();
-
-   if (mTrackArtist) {
-      mTrackArtist->UpdatePrefs();
-   }
-
    // All vertical rulers must be recalculated since the minimum and maximum
    // frequences may have been changed.
    UpdateVRulers();

src/TrackPanel.h

@@ -20,6 +20,7 @@
 #include <wx/timer.h> // to inherit
 
 #include "HitTestResult.h"
+#include "Prefs.h"
 
 #include "SelectedRegion.h"
 
@@ -210,6 +211,8 @@ namespace TrackInfo
        wxWindow *pParent);
 #endif
 
+   // Non-member, namespace function relying on TrackPanel to invoke it
+   // when it handles preference update events
    void UpdatePrefs( wxWindow *pParent );
 };
 
@@ -251,6 +254,7 @@ enum : int {
 class AUDACITY_DLL_API TrackPanel final
    : public CellularPanel
    , public NonKeystrokeInterceptingWindow
+   , private PrefsListener
 {
  public:
    TrackPanel(wxWindow * parent,
@@ -264,7 +268,7 @@ class AUDACITY_DLL_API TrackPanel final
 
    virtual ~ TrackPanel();
 
-   void UpdatePrefs();
+   void UpdatePrefs() override;
    void ApplyUpdatedTheme();
 
    void OnPaint(wxPaintEvent & event);

src/ViewInfo.cpp

@@ -146,6 +146,14 @@ ViewInfo::ViewInfo(double start, double screenDuration, double pixelsPerSecond)
    UpdatePrefs();
 }
 
+void ViewInfo::UpdateSelectedPrefs( int id )
+{
+   if (id == UpdateScrollPrefsID())
+      gPrefs->Read(wxT("/GUI/AutoScroll"), &bUpdateTrackIndicator,
+                   true);
+   ZoomInfo::UpdateSelectedPrefs( id );
+}
+
 void ViewInfo::UpdatePrefs()
 {
    ZoomInfo::UpdatePrefs();
@@ -155,6 +163,8 @@ void ViewInfo::UpdatePrefs()
 #endif
    gPrefs->Read(wxT("/GUI/AdjustSelectionEdges"), &bAdjustSelectionEdges,
       true);
+
+   UpdateSelectedPrefs( UpdateScrollPrefsID() );
 }
 
 void ViewInfo::SetBeforeScreenWidth(wxInt64 beforeWidth, wxInt64 screenWidth, double lowerBoundTime)
@@ -206,3 +216,9 @@ void ViewInfo::OnTimer(wxCommandEvent &event)
    // Propagate the message to other listeners bound to this
    this->ProcessEvent( event );
 }
+
+int ViewInfo::UpdateScrollPrefsID()
+{
+   static int value = wxNewId();
+   return value;
+}

src/ViewInfo.h

@@ -15,6 +15,7 @@
 #include <wx/event.h> // inherit wxEvtHandler
 #include "SelectedRegion.h"
 #include "MemoryX.h"
+#include "Prefs.h"
 
 
 class Track;
@@ -31,6 +32,7 @@ class Track;
 class AUDACITY_DLL_API ZoomInfo /* not final */
    // Note that ViewInfo inherits from ZoomInfo but there are no virtual functions.
    // That's okay if we pass always by reference and never copy, suffering "slicing."
+: protected PrefsListener
 {
 public:
    ZoomInfo(double start, double pixelsPerSecond);
@@ -40,7 +42,7 @@ public:
    ZoomInfo(const ZoomInfo&) PROHIBITED;
    ZoomInfo& operator= (const ZoomInfo&) PROHIBITED;
 
-   void UpdatePrefs();
+   void UpdatePrefs() override;
 
    int vpos;                    // vertical scroll pos
 
@@ -146,7 +148,9 @@ class AUDACITY_DLL_API ViewInfo final
 public:
    ViewInfo(double start, double screenDuration, double pixelsPerSecond);
 
-   void UpdatePrefs();
+   static int UpdateScrollPrefsID();
+   void UpdatePrefs() override;
+   void UpdateSelectedPrefs( int id ) override;
 
    double GetBeforeScreenWidth() const
    {

src/menus/ViewMenus.cpp

@@ -10,6 +10,7 @@
 #include "../TrackPanel.h"
 #include "../commands/CommandContext.h"
 #include "../commands/CommandManager.h"
+#include "../prefs/GUIPrefs.h"
 #include "../prefs/TracksPrefs.h"
 
 #ifdef EXPERIMENTAL_EFFECTS_RACK
@@ -367,7 +368,10 @@ void OnShowClipping(const CommandContext &context)
    gPrefs->Write(wxT("/GUI/ShowClipping"), checked);
    gPrefs->Flush();
    commandManager->Check(wxT("ShowClipping"), checked);
-   trackPanel->UpdatePrefs();
+
+   wxTheApp->AddPendingEvent(wxCommandEvent{
+      EVT_PREFS_UPDATE, ShowClippingPrefsID() });
+
    trackPanel->Refresh(false);
 }
 

src/prefs/GUIPrefs.cpp

@@ -366,6 +366,12 @@ wxString GUIPrefs::GetLang()
       return {};
 }
 
+int ShowClippingPrefsID()
+{
+   static int value = wxNewId();
+   return value;
+}
+
 PrefsPanel::Factory
 GUIPrefsFactory = [](wxWindow *parent, wxWindowID winid)
 {

src/prefs/GUIPrefs.h

@@ -67,4 +67,7 @@ class GUIPrefs final : public PrefsPanel
 
 /// A PrefsPanel::Factory that creates one GUIPrefs panel.
 extern PrefsPanel::Factory GUIPrefsFactory;
+
+int ShowClippingPrefsID();
+
 #endif

src/prefs/PrefsDialog.cpp

@@ -850,9 +850,6 @@ void PrefsDialog::OnOK(wxCommandEvent & WXUNUSED(event))
    // LL:  wxMac can't handle recreating the menus when this dialog is still active,
    //      so AudacityProject::UpdatePrefs() or any of the routines it calls must
    //      not cause MenuCreator::RebuildMenuBar() to be executed.
-   for (size_t i = 0; i < gAudacityProjects.size(); i++) {
-      gAudacityProjects[i]->UpdatePrefs();
-   }
 
    wxTheApp->AddPendingEvent(wxCommandEvent{ EVT_PREFS_UPDATE });
 

src/toolbars/ControlToolBar.cpp

@@ -127,6 +127,7 @@ ControlToolBar::~ControlToolBar()
 void ControlToolBar::Create(wxWindow * parent)
 {
    ToolBar::Create(parent);
+   UpdatePrefs();
 }
 
 // This is a convenience function that allows for button creation in

src/toolbars/DeviceToolBar.cpp

@@ -64,6 +64,12 @@ BEGIN_EVENT_TABLE(DeviceToolBar, ToolBar)
    EVT_COMMAND(wxID_ANY, EVT_CAPTURE_KEY, DeviceToolBar::OnCaptureKey)
 END_EVENT_TABLE()
 
+static int DeviceToolbarPrefsID()
+{
+   static int value = wxNewId();
+   return value;
+}
+
 //Standard contructor
 DeviceToolBar::DeviceToolBar()
 : ToolBar(DeviceBarID, _("Device"), wxT("Device"), true)
@@ -313,6 +319,13 @@ void DeviceToolBar::UpdatePrefs()
    Refresh();
 }
 
+void DeviceToolBar::UpdateSelectedPrefs( int id )
+{
+   if (id == DeviceToolbarPrefsID())
+      UpdatePrefs();
+   ToolBar::UpdateSelectedPrefs( id );
+}
+
 
 void DeviceToolBar::EnableDisableButtons()
 {
@@ -773,10 +786,8 @@ void DeviceToolBar::OnChoice(wxCommandEvent &event)
       gAudioIO->HandleDeviceChange();
    }
 
-   // Update all projects' DeviceToolBar.
-   for (size_t i = 0; i < gAudacityProjects.size(); i++) {
-      gAudacityProjects[i]->GetDeviceToolBar()->UpdatePrefs();
-   }
+   wxTheApp->AddPendingEvent(wxCommandEvent{
+      EVT_PREFS_UPDATE, DeviceToolbarPrefsID() });
 }
 
 void DeviceToolBar::ShowInputDialog()

src/toolbars/DeviceToolBar.h

@@ -29,6 +29,7 @@ class DeviceToolBar final : public ToolBar {
    void Create(wxWindow * parent) override;
 
    void UpdatePrefs() override;
+   void UpdateSelectedPrefs( int ) override;
 
    void DeinitChildren();
    void Populate() override;

src/toolbars/EditToolBar.cpp

@@ -89,6 +89,7 @@ EditToolBar::~EditToolBar()
 void EditToolBar::Create(wxWindow * parent)
 {
    ToolBar::Create(parent);
+   UpdatePrefs();
 }
 
 void EditToolBar::AddSeparator()

src/toolbars/MeterToolBar.cpp

@@ -78,6 +78,8 @@ void MeterToolBar::Create(wxWindow * parent)
 {
    ToolBar::Create(parent);
 
+   UpdatePrefs();
+
    // Simulate a size event to set initial meter placement/size
    wxSizeEvent dummy;
    OnSize(dummy);
@@ -156,18 +158,6 @@ void MeterToolBar::Populate()
 
 void MeterToolBar::UpdatePrefs()
 {
-   if( mPlayMeter )
-   {
-      mPlayMeter->UpdatePrefs();
-      mPlayMeter->Refresh();
-   }
-
-   if( mRecordMeter )
-   {
-      mRecordMeter->UpdatePrefs();
-      mRecordMeter->Refresh();
-   }
-
    RegenerateTooltips();
 
    // Set label to pull in language change
@@ -175,8 +165,6 @@ void MeterToolBar::UpdatePrefs()
 
    // Give base class a chance
    ToolBar::UpdatePrefs();
-
-
 }
 
 void MeterToolBar::RegenerateTooltips()

src/toolbars/MixerToolBar.cpp

@@ -67,6 +67,7 @@ MixerToolBar::~MixerToolBar()
 void MixerToolBar::Create(wxWindow *parent)
 {
    ToolBar::Create(parent);
+   UpdatePrefs();
 }
 
 void MixerToolBar::Populate()

src/toolbars/ScrubbingToolBar.cpp

@@ -68,6 +68,7 @@ ScrubbingToolBar::~ScrubbingToolBar()
 void ScrubbingToolBar::Create(wxWindow * parent)
 {
    ToolBar::Create(parent);
+   UpdatePrefs();
 }
 
 /// This is a convenience function that allows for button creation in

src/toolbars/SelectionBar.cpp

@@ -132,6 +132,7 @@ SelectionBar::~SelectionBar()
 void SelectionBar::Create(wxWindow * parent)
 {
    ToolBar::Create(parent);
+   UpdatePrefs();
 }
 
 
@@ -504,7 +505,8 @@ void SelectionBar::OnUpdate(wxCommandEvent &evt)
    // Save format name before recreating the controls so they resize properly
    {
       auto format = mStartTime->GetBuiltinName(index);
-      mListener->AS_SetSelectionFormat(format);
+      if (mListener)
+         mListener->AS_SetSelectionFormat(format);
    }
 
    RegenerateTooltips();

src/toolbars/SpectralSelectionBar.cpp

@@ -107,6 +107,7 @@ SpectralSelectionBar::~SpectralSelectionBar()
 void SpectralSelectionBar::Create(wxWindow * parent)
 {
    ToolBar::Create(parent);
+   UpdatePrefs();
    mHeight = wxWindowBase::GetSizer()->GetSize().GetHeight();
 }
 
@@ -370,12 +371,14 @@ void SpectralSelectionBar::OnUpdate(wxCommandEvent &evt)
    if (type == EVT_FREQUENCYTEXTCTRL_UPDATED) {
       NumericTextCtrl *frequencyCtrl = (mbCenterAndWidth ? mCenterCtrl : mLowCtrl);
       auto frequencyFormatName = frequencyCtrl->GetBuiltinName(index);
-      mListener->SSBL_SetFrequencySelectionFormatName(frequencyFormatName);
+      if (mListener)
+         mListener->SSBL_SetFrequencySelectionFormatName(frequencyFormatName);
    }
    else if (mbCenterAndWidth &&
             type == EVT_BANDWIDTHTEXTCTRL_UPDATED) {
       auto bandwidthFormatName = mWidthCtrl->GetBuiltinName(index);
-      mListener->SSBL_SetBandwidthSelectionFormatName(bandwidthFormatName);
+      if (mListener)
+         mListener->SSBL_SetBandwidthSelectionFormatName(bandwidthFormatName);
    }
 
    // ToolBar::ReCreateButtons() will get rid of our sizers and controls

src/toolbars/ToolBar.h

@@ -18,6 +18,7 @@
 #include <vector>
 #include <wx/defs.h>
 
+#include "../Prefs.h"
 #include "../Theme.h"
 #include "../widgets/wxPanelWrapper.h" // to inherit
 
@@ -84,7 +85,9 @@ enum
 // How may pixels padding each side of a floating toolbar
 enum { ToolBarFloatMargin = 1 };
 
-class ToolBar /* not final */ : public wxPanelWrapper
+class ToolBar /* not final */
+: public wxPanelWrapper
+, protected PrefsListener
 {
 
  public:
@@ -101,7 +104,7 @@ class ToolBar /* not final */ : public wxPanelWrapper
    virtual void Create(wxWindow *parent);
    virtual void EnableDisableButtons() = 0;
    virtual void ReCreateButtons();
-   virtual void UpdatePrefs();
+   void UpdatePrefs() override;
    virtual void RegenerateTooltips() = 0;
 
    int GetType();

src/toolbars/ToolManager.cpp

@@ -1091,21 +1091,6 @@ void ToolManager::LayoutToolBars()
    mBotDock->LayoutToolBars();
 }
 
-//
-// Tell the toolbars that preferences have been updated
-//
-void ToolManager::UpdatePrefs()
-{
-   for( int ndx = 0; ndx < ToolBarCount; ndx++ )
-   {
-      ToolBar *bar = mBars[ ndx ].get();
-      if( bar )
-      {
-         bar->UpdatePrefs();
-      }
-   }
-}
-
 //
 // Handle toolbar dragging
 //

src/toolbars/ToolManager.h

@@ -48,7 +48,6 @@ class ToolManager final : public wxEvtHandler, public wxEventFilter
    ~ToolManager();
 
    void LayoutToolBars();
-   void UpdatePrefs();
 
    bool IsDocked( int type );
 

src/toolbars/ToolsToolBar.cpp

@@ -258,3 +258,9 @@ void ToolsToolBar::OnTool(wxCommandEvent & evt)
                  IsDown(multiTool));
    gPrefs->Flush();
 }
+
+void ToolsToolBar::Create(wxWindow * parent)
+{
+   ToolBar::Create(parent);
+   UpdatePrefs();
+}

src/toolbars/ToolsToolBar.h

@@ -68,6 +68,7 @@ class ToolsToolBar final : public ToolBar {
 
  private:
 
+   void Create(wxWindow * parent) override;
    void RegenerateTooltips() override;
    wxImage *MakeToolImage(wxImage *tool, wxImage *mask, int style);
    static AButton *MakeTool(

src/toolbars/TranscriptionToolBar.h

@@ -98,7 +98,6 @@ class TranscriptionToolBar final : public ToolBar {
    //void Populate() override;
    //void Repaint(wxDC * WXUNUSED(dc)) override {}
    //void EnableDisableButtons() override;
-   //void UpdatePrefs() override;
 
    //void OnFocus(wxFocusEvent &event);
    //void OnCaptureKey(wxCommandEvent &event);

src/widgets/Meter.cpp

@@ -253,9 +253,6 @@ bool MeterUpdateQueue::Get(MeterUpdateMsg &msg)
 // How many pixels between items?
 const static int gap = 2;
 
-// Event used to notify all meters of preference changes
-wxDEFINE_EVENT(EVT_METER_PREFERENCES_CHANGED, wxCommandEvent);
-
 const static wxChar *PrefStyles[] =
 {
    wxT("AutomaticStereo"),
@@ -348,11 +345,6 @@ MeterPanel::MeterPanel(AudacityProject *project,
    mPeakPeakPen = wxPen(theTheme.Colour( clrMeterPeak),        1, wxPENSTYLE_SOLID);
    mDisabledPen = wxPen(theTheme.Colour( clrMeterDisabledPen), 1, wxPENSTYLE_SOLID);
 
-   // Register for our preference update event
-   wxTheApp->Bind(EVT_METER_PREFERENCES_CHANGED,
-                     &MeterPanel::OnMeterPrefsUpdated,
-                     this);
-
    if (mIsInput) {
       wxTheApp->Bind(EVT_AUDIOIO_MONITOR,
                         &MeterPanel::OnAudioIOStatus,
@@ -457,6 +449,20 @@ void MeterPanel::UpdatePrefs()
    Reset(mRate, false);
 
    mLayoutValid = false;
+
+   Refresh(false);
+}
+
+static int MeterPrefsID()
+{
+   static int value = wxNewId();
+   return value;
+}
+
+void MeterPanel::UpdateSelectedPrefs(int id)
+{
+   if (id == MeterPrefsID())
+      UpdatePrefs();
 }
 
 void MeterPanel::OnErase(wxEraseEvent & WXUNUSED(event))
@@ -1964,15 +1970,6 @@ void MeterPanel::OnMonitor(wxCommandEvent & WXUNUSED(event))
    StartMonitoring();
 }
 
-void MeterPanel::OnMeterPrefsUpdated(wxCommandEvent & evt)
-{
-   evt.Skip();
-
-   UpdatePrefs();
-
-   Refresh(false);
-}
-
 void MeterPanel::OnPreferences(wxCommandEvent & WXUNUSED(event))
 {
    wxTextCtrl *rate;
@@ -2099,9 +2096,8 @@ void MeterPanel::OnPreferences(wxCommandEvent & WXUNUSED(event))
       // Currently, there are 2 playback meters and 2 record meters and any number of 
       // mixerboard meters, so we have to send out an preferences updated message to
       // ensure they all update themselves.
-      wxCommandEvent e(EVT_METER_PREFERENCES_CHANGED);
-      e.SetEventObject(this);
-      GetParent()->GetEventHandler()->ProcessEvent(e);
+      wxTheApp->AddPendingEvent(wxCommandEvent{
+         EVT_PREFS_UPDATE, MeterPrefsID() });
    }
 }
 

src/widgets/Meter.h

@@ -22,14 +22,11 @@
 #include <wx/timer.h> // member variable
 
 #include "../SampleFormat.h"
+#include "../Prefs.h"
 #include "Ruler.h" // member variable
 
 class AudacityProject;
 
-// Event used to notify all meters of preference changes
-wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API,
-                         EVT_METER_PREFERENCES_CHANGED, wxCommandEvent);
-
 // Increase this when we add support for multichannel meters
 // (most of the code is already there)
 const int kMaxMeterBars = 2;
@@ -94,7 +91,7 @@ class MeterAx;
 \brief MeterPanel is a panel that paints the meter used for monitoring
 or playback.
 ************************************************************************/
-class MeterPanel final : public wxPanelWrapper
+class MeterPanel final : public wxPanelWrapper, private PrefsListener
 {
    DECLARE_DYNAMIC_CLASS(MeterPanel)
 
@@ -124,7 +121,6 @@ class MeterPanel final : public wxPanelWrapper
 
    void SetFocusFromKbd() override;
 
-   void UpdatePrefs();
    void Clear();
 
    Style GetStyle() const { return mStyle; }
@@ -192,6 +188,9 @@ class MeterPanel final : public wxPanelWrapper
    int GetDBRange() const { return mDB ? mDBRange : -1; }
 
  private:
+   void UpdatePrefs() override;
+   void UpdateSelectedPrefs( int ) override;
+
    static bool s_AcceptsFocus;
    struct Resetter { void operator () (bool *p) const { if(p) *p = false; } };
    using TempAllowFocus = std::unique_ptr<bool, Resetter>;
@@ -232,7 +231,6 @@ class MeterPanel final : public wxPanelWrapper
    void ShowMenu(const wxPoint & pos);
    void OnMonitor(wxCommandEvent &evt);
    void OnPreferences(wxCommandEvent &evt);
-   void OnMeterPrefsUpdated(wxCommandEvent &evt);
 
    wxString Key(const wxString & key) const;