Some uses of wxWindowRef, a weak pointer that won't become dangling

src/toolbars/ToolBar.cpp

@@ -90,7 +90,7 @@ private:
    ToolBar *mBar;
    wxPoint mResizeOffset;
    wxSize mOrigSize;
-   wxWindow *mOrigFocus{};
+   wxWindowRef mOrigFocus{};
 
    DECLARE_EVENT_TABLE()
 };

src/toolbars/ToolManager.cpp

@@ -634,15 +634,9 @@ int ToolManager::FilterEvent(wxEvent &event)
            !dynamic_cast<Grabber*>( window ) &&
            !dynamic_cast<ToolFrame*>( window ) &&
            top == mParent )
+         // Note this is a dangle-proof wxWindowRef:
          mLastFocus = window;
    }
-   else if (event.GetEventType() == wxEVT_DESTROY) {
-      auto &closeEvent = static_cast<wxWindowDestroyEvent&>(event);
-      auto window = closeEvent.GetEventObject();
-      if (window == mLastFocus)
-         // Avoid a dangling pointer!
-         mLastFocus = nullptr;
-   }
 
    return Event_Skip;
 }

src/toolbars/ToolManager.h

@@ -93,7 +93,7 @@ class ToolManager final : public wxEvtHandler, public wxEventFilter
    void Updated();
 
    AudacityProject *mParent;
-   wxWindow *mLastFocus{};
+   wxWindowRef mLastFocus{};
 
    ToolFrame *mDragWindow;
    ToolDock *mDragDock;

src/widgets/ProgressDialog.cpp

@@ -1043,10 +1043,8 @@ ProgressDialog::~ProgressDialog()
 
    // Restore saved focus, but only if the window still exists.
    //
-   // It is possible that it was a deferred deletion and it was deleted since
-   // we captured the focused window.  So, we need to verify that the window
-   // still exists by searching all of the wxWidgets windows.  It's the only
-   // sure way.
+   // PRL:  I'm conservatively preserving the old existence test, but I think
+   // it's redundant now that we use wxWindowRef to avoid a dangling pointer
    if (mHadFocus && SearchForWindow(wxTopLevelWindows, mHadFocus)) {
       mHadFocus->SetFocus();
    }

src/widgets/ProgressDialog.h

@@ -105,7 +105,7 @@ public:
    void SetMessage(const wxString & message);
 
 protected:
-   wxWeakRef<wxWindow> mHadFocus;
+   wxWindowRef mHadFocus;
 
    wxStaticText *mElapsed;
    wxStaticText *mRemaining;