Enh 66 again: do not make duplicate About dialogs on Mac

src/AboutDialog.cpp

@@ -223,11 +223,23 @@ END_EVENT_TABLE()
 
 IMPLEMENT_CLASS(AboutDialog, wxDialog)
 
+namespace {
+   AboutDialog *sActiveInstance{};
+}
+
+AboutDialog *AboutDialog::ActiveIntance()
+{
+   return sActiveInstance;
+}
+
 AboutDialog::AboutDialog(wxWindow * parent)
    :  wxDialog(parent, -1, _("About Audacity"),
                wxDefaultPosition, wxDefaultSize,
                wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER)
 {
+   wxASSERT(!sActiveInstance);
+   sActiveInstance = this;
+
    SetName(GetTitle());
    this->SetBackgroundColour(theTheme.Colour( clrAboutBoxBackground ));
    icon = NULL;
@@ -964,12 +976,16 @@ void AboutDialog::AddBuildinfoRow( wxString* htmlstring, const wxChar * libname,
    *htmlstring += wxT("</td></tr>");
 }
 
-
 AboutDialog::~AboutDialog()
 {
+   sActiveInstance = {};
 }
 
 void AboutDialog::OnOK(wxCommandEvent & WXUNUSED(event))
 {
+#ifdef __WXMAC__
+   Destroy();
+#else
    EndModal(wxID_OK);
+#endif
 }

src/AboutDialog.h

@@ -56,11 +56,13 @@ class AboutDialog final : public wxDialog {
    AboutDialog(wxWindow * parent);
    virtual ~ AboutDialog();
 
+   static AboutDialog *ActiveIntance();
+
    void OnOK(wxCommandEvent & event);
 
    wxStaticBitmap *icon;
 
-    DECLARE_EVENT_TABLE()
+   DECLARE_EVENT_TABLE()
 
  private:
    enum Role {

src/AudacityApp.cpp

@@ -2030,21 +2030,19 @@ int AudacityApp::OnExit()
 void AudacityApp::OnMenuAbout(wxCommandEvent & event)
 {
    // This function shadows a similar function
-   // in Menus.cpp, but should only be used on the Mac platform
-   // when no project windows are open. This check assures that
-   // this happens, and enable the same code to be present on
-   // all platforms.
-   if(gAudacityProjects.GetCount() == 0) {
+   // in Menus.cpp, but should only be used on the Mac platform.
 #ifdef __WXMAC__
-      // Modeless dialog, consistent with other Mac applications
+   // Modeless dialog, consistent with other Mac applications
+   // Not more than one at once!
+   const auto instance = AboutDialog::ActiveIntance();
+   if (instance)
+      instance->Raise();
+   else
+      // This dialog deletes itself when dismissed
       (safenew AboutDialog{ nullptr })->Show(true);
 #else
-      AboutDialog dlog(NULL);
-      dlog.ShowModal();
+      wxASSERT(false);
 #endif
-   }
-   else
-      event.Skip();
 }
 
 void AudacityApp::OnMenuNew(wxCommandEvent & event)

src/Menus.cpp

@@ -6604,7 +6604,8 @@ void AudacityProject::OnAbout()
 {
 #ifdef __WXMAC__
    // Modeless dialog, consistent with other Mac applications
-   (safenew AboutDialog{ nullptr })->Show(true);
+   wxCommandEvent dummy;
+   wxGetApp().OnMenuAbout(dummy);
 #else
    // Windows and Linux still modal.
    AboutDialog dlog(this);