added wxAppTraits::CreateRenderer() which may be used to customize the renderer

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@22341 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/window.h

@@ -831,7 +831,17 @@ public:
     wxSizer *GetSizer() const { return m_windowSizer; }
 
     // Track if this window is a member of a sizer
-    void SetContainingSizer(wxSizer* sizer) { m_containingSizer = sizer; }
+    void SetContainingSizer(wxSizer* sizer)
+    {
+        // adding a window to a sizer twice is going to result in fatal and
+        // hard to debug problems later because when deleting the second
+        // associated wxSizerItem we're going to dereference a dangling
+        // pointer; so try to detect this as early as possible
+        wxASSERT_MSG( !sizer || m_containingSizer != sizer,
+                        _T("Adding a window to the same sizer twice?") );
+
+        m_containingSizer = sizer;
+    }
     wxSizer *GetContainingSizer() const { return m_containingSizer; }
 
     // accessibility