Move project status string management to new attached object class

src/ProjectStatus.h

@@ -0,0 +1,49 @@
+/**********************************************************************
+
+Audacity: A Digital Audio Editor
+
+ProjectStatus.h
+
+Paul Licameli
+
+**********************************************************************/
+
+#ifndef __AUDACITY_PROJECT_STATUS__
+#define __AUDACITY_PROJECT_STATUS__
+#endif
+
+#include <wx/event.h> // to declare custom event type
+#include "ClientData.h" // to inherit
+
+class AudacityProject;
+class wxWindow;
+
+enum StatusBarField : int {
+   stateStatusBarField = 1,
+   mainStatusBarField = 2,
+   rateStatusBarField = 3
+};
+
+// Type of event emitted by the project when its status message is set
+wxDECLARE_EXPORTED_EVENT(AUDACITY_DLL_API,
+                         EVT_PROJECT_STATUS_UPDATE, wxCommandEvent);
+
+class ProjectStatus final
+   : public ClientData::Base
+{
+public:
+   static ProjectStatus &Get( AudacityProject &project );
+   static const ProjectStatus &Get( const AudacityProject &project );
+
+   explicit ProjectStatus( AudacityProject &project );
+   ProjectStatus( const ProjectStatus & ) = delete;
+   ProjectStatus &operator= ( const ProjectStatus & ) = delete;
+   ~ProjectStatus() override;
+
+   const wxString &Get() const { return mLastMainStatusMessage; }
+   void Set(const wxString &msg);
+
+private:
+   AudacityProject &mProject;
+   wxString mLastMainStatusMessage;
+};