Define BasicUI::WindowPlacement and subclass for wxWidgets...

... An elaborate way to hold a wxWindow* as parent of a window, but avoiding
mention of wxWindow* in the member functions of BasicUI::Services, to be defined
next

libraries/lib-basic-ui/BasicUI.cpp

@@ -13,6 +13,8 @@ Paul Licameli
 #include <vector>
 
 namespace  BasicUI {
+WindowPlacement::~WindowPlacement() = default;
+
 Services::~Services() = default;
 
 static Services *theInstance = nullptr;

libraries/lib-basic-ui/BasicUI.h

@@ -20,6 +20,20 @@ namespace BasicUI {
 
 using Action = std::function<void()>;
 
+//! Subclasses may hold information such as a parent window pointer for a dialog.
+/*! The default-constructed empty value of this base class must be accepted by overrides of methods of
+ Services */
+class BASIC_UI_API WindowPlacement {
+public:
+   WindowPlacement() = default;
+
+   //! Don't slice
+   WindowPlacement( const WindowPlacement& ) PROHIBITED;
+   //! Don't slice
+   WindowPlacement &operator=( const WindowPlacement& ) PROHIBITED;
+   virtual ~WindowPlacement();
+};
+
 //! @}
 
 //! Abstract class defines a few user interface services, not mentioning particular toolkits

src/widgets/wxWidgetsBasicUI.cpp

@@ -12,6 +12,8 @@ Paul Licameli
 
 using namespace BasicUI;
 
+wxWidgetsWindowPlacement::~wxWidgetsWindowPlacement() = default;
+
 wxWidgetsBasicUI::~wxWidgetsBasicUI() = default;
 
 void wxWidgetsBasicUI::DoCallAfter(const Action &action)
@@ -23,3 +25,13 @@ void wxWidgetsBasicUI::DoYield()
 {
    wxTheApp->Yield();
 }
+
+namespace {
+wxWindow *GetParent(const BasicUI::WindowPlacement &placement)
+{
+   if (auto *pPlacement =
+       dynamic_cast<const wxWidgetsWindowPlacement*>(&placement))
+      return pPlacement->pWindow;
+   return nullptr;
+}
+}

src/widgets/wxWidgetsBasicUI.h

@@ -13,6 +13,20 @@ Paul Licameli
 
 #include "BasicUI.h"
 
+class wxWindow;
+
+//! Window placement information for wxWidgetsBasicUI can be constructed from a wxWindow pointer
+struct AUDACITY_DLL_API wxWidgetsWindowPlacement final
+: BasicUI::WindowPlacement {
+   wxWidgetsWindowPlacement() = default;
+   explicit wxWidgetsWindowPlacement( wxWindow *pWindow )
+      : pWindow{ pWindow }
+   {}
+
+   ~wxWidgetsWindowPlacement() override;
+   wxWindow *pWindow{};
+};
+
 //! An implementation of BasicUI::Services in terms of the wxWidgets toolkit
 /*! This is a singleton that doesn't need AUDACITY_DLL_API visibility */
 class wxWidgetsBasicUI final : public BasicUI::Services {