define PrefsPanel::Registration

src/prefs/PrefsDialog.cpp

@@ -477,7 +477,36 @@ int wxTreebookExt::SetSelection(size_t n)
    return i;
 }
 
+namespace {
+   struct Entry{
+      unsigned sequenceNumber;
+      PrefsDialog::PrefsNode node;
 
+      bool operator < ( const Entry &other ) const
+      { return sequenceNumber < other.sequenceNumber; }
+   };
+   using Entries = std::vector< Entry >;
+   Entries &Registry()
+   {
+      static Entries result;
+      return result;
+   }
+}
+
+PrefsPanel::Registration::Registration( unsigned sequenceNumber,
+   const Factory &factory,
+   unsigned nChildren,
+   bool expanded )
+{
+   auto &registry = Registry();
+   Entry entry{ sequenceNumber, { factory, nChildren, expanded } };
+   const auto end = registry.end();
+   // Find insertion point:
+   auto iter = std::lower_bound( registry.begin(), end, entry );
+   // There should not be duplicate sequence numbers:
+   wxASSERT( iter == end || entry < *iter );
+   registry.insert( iter, entry );
+}
 
 PrefsDialog::Factories
 &PrefsDialog::DefaultFactories()

src/prefs/PrefsDialog.h

@@ -39,11 +39,11 @@ class PrefsDialog /* not final */ : public wxDialogWrapper
          std::function< PrefsPanel * (
             wxWindow *parent, wxWindowID winid, AudacityProject *) >;
        Factory factory;
-       CONST int nChildren;
+       unsigned nChildren;
        bool expanded;
 
        PrefsNode(const Factory &factory_,
-          int nChildren_ = 0,
+          unsigned nChildren_ = 0,
           bool expanded_ = true)
           : factory(factory_), nChildren(nChildren_), expanded(expanded_)
        {}

src/prefs/PrefsPanel.h

@@ -49,7 +49,7 @@ class PrefsPanel /* not final */ : public wxPanelWrapper, ComponentInterface
 {
  public:
    // \brief Type alias for factories such as GUIPrefsFactory that produce a
-   // PrefsPanel.
+   // PrefsPanel, used by the Preferences dialog in a treebook.
    // The project pointer may be null.  Usually it's not needed because
    // preferences are global.  But sometimes you need a project, such as to
    // preview the preference changes for spectrograms.
@@ -57,8 +57,18 @@ class PrefsPanel /* not final */ : public wxPanelWrapper, ComponentInterface
       std::function< PrefsPanel * (
          wxWindow *parent, wxWindowID winid, AudacityProject *) >;
 
-   PrefsPanel(
-      wxWindow * parent, wxWindowID winid, const TranslatableString &title)
+   // Typically you make a static object of this type in the .cpp file that
+   // also implements the PrefsPanel subclass.
+   struct Registration final
+   {
+      Registration( unsigned sequenceNumber,
+         const Factory &factory,
+         unsigned nChildren = 0,
+         bool expanded = true );
+   };
+
+   PrefsPanel(wxWindow * parent,
+      wxWindowID winid, const TranslatableString &title)
    :  wxPanelWrapper(parent, winid)
    {
       SetLabel(title);     // Provide visual label