Manage TrackPanelResizerCell by shared_ptr, no singleton

src/Track.h

@@ -38,6 +38,7 @@ class LabelTrack;
 class TimeTrack;
 class TrackControls;
 class TrackVRulerControls;
+class TrackPanelResizerCell;
 class WaveTrack;
 class NoteTrack;
 class AudacityProject;
@@ -144,6 +145,10 @@ class AUDACITY_DLL_API Track /* not final */
    // mouse actions for the vertical ruler
    std::shared_ptr<TrackPanelCell> GetVRulerControl();
 
+   // Return another, associated TrackPanelCell object that implements the
+   // click and drag to resize
+   std::shared_ptr<TrackPanelCell> GetResizer();
+
    // This just returns a constant and can be overriden by subclasses
    // to specify a different height for the case that the track is minimized.
    virtual int GetMinimizedHeight() const;
@@ -302,6 +307,7 @@ protected:
    // These hold the controls:
    std::shared_ptr<TrackControls> mpControls;
    std::shared_ptr<TrackVRulerControls> mpVRulerContols;
+   std::shared_ptr<TrackPanelResizerCell> mpResizer;
 };
 
 class AUDACITY_DLL_API AudioTrack /* not final */ : public Track

src/TrackPanel.cpp

@@ -3118,9 +3118,7 @@ TrackPanelCellIterator &TrackPanelCellIterator::operator++ ()
             mpCell = mpTrack->GetVRulerControl().get();
             break;
          case CellType::Resizer: {
-            auto instance = &TrackPanelResizerCell::Instance();
-            instance->mpTrack = mpTrack;
-            mpCell = instance;
+            mpCell = mpTrack->GetResizer().get();
             break;
          }
          default:

src/TrackPanelResizeHandle.cpp

@@ -384,11 +384,9 @@ UIHandle::Result TrackPanelResizeHandle::Cancel(AudacityProject *pProject)
    return RefreshCode::RefreshAll;
 }
 
-TrackPanelResizerCell &TrackPanelResizerCell::Instance()
-{
-   static TrackPanelResizerCell instance;
-   return instance;
-}
+TrackPanelResizerCell::TrackPanelResizerCell( std::shared_ptr<Track> pTrack )
+   : mpTrack{ pTrack }
+{}
 
 HitTestResult TrackPanelResizerCell::HitTest
 (const TrackPanelMouseEvent &event, const AudacityProject *pProject)

src/TrackPanelResizeHandle.h

@@ -68,20 +68,21 @@ private:
 
 class TrackPanelResizerCell : public CommonTrackPanelCell
 {
-   TrackPanelResizerCell() {}
    TrackPanelResizerCell(const TrackPanelResizerCell&) = delete;
    TrackPanelResizerCell &operator= (const TrackPanelResizerCell&) = delete;
 public:
-   static TrackPanelResizerCell &Instance();
+
+   explicit
+   TrackPanelResizerCell( std::shared_ptr<Track> pTrack );
 
    HitTestResult HitTest
       (const TrackPanelMouseEvent &event,
        const AudacityProject *pProject) override;
 
-   Track *FindTrack() override { return mpTrack; };
+   Track *FindTrack() override { return mpTrack.lock().get(); };
 private:
    friend class TrackPanelCellIterator;
-   Track *mpTrack {};
+   std::weak_ptr<Track> mpTrack;
    bool mBetweenTracks {};
 };
 

src/tracks/ui/TrackUI.cpp

@@ -74,3 +74,12 @@ std::shared_ptr<TrackPanelCell> Track::GetVRulerControl()
       mpVRulerContols = GetVRulerControls();
    return mpVRulerContols;
 }
+
+#include "TrackPanelResizeHandle.h"
+std::shared_ptr<TrackPanelCell> Track::GetResizer()
+{
+   if (!mpResizer)
+      // create on demand
+      mpResizer = std::make_shared<TrackPanelResizerCell>( Pointer( this ) );
+   return mpResizer;
+}