adding comment

[wxWidgets.git] / include / wx / gdiobj.h

diff --git a/include/wx/gdiobj.h b/include/wx/gdiobj.h
index ebe33197534f3fa0c014912dbb6a9895432ca182..0c251cc9d60d14ea2dec72b83b671149a00fd237 100644 (file)
--- a/include/wx/gdiobj.h
+++ b/include/wx/gdiobj.h
@@ -20,23 +20,44 @@
 // the same native GDI object
 // ----------------------------------------------------------------------------
 
-class WXDLLIMPEXP_FWD_CORE wxGDIRefData: public wxObjectRefData { };
+class WXDLLIMPEXP_CORE wxGDIRefData : public wxObjectRefData
+{
+public:
+    // Default ctor which needs to be defined just because we use
+    // wxDECLARE_NO_COPY_CLASS() below.
+    wxGDIRefData() { }
+
+    // override this in the derived classes to check if this data object is
+    // really fully initialized
+    virtual bool IsOk() const { return true; }
+
+private:
+    wxDECLARE_NO_COPY_CLASS(wxGDIRefData);
+};
 
 // ----------------------------------------------------------------------------
-// wxGDIObject
+// wxGDIObject: base class for bitmaps, pens, brushes, ...
 // ----------------------------------------------------------------------------
 
-class WXDLLIMPEXP_CORE wxGDIObject: public wxObject
+class WXDLLIMPEXP_CORE wxGDIObject : public wxObject
 {
 public:
+    // checks if the object can be used
+    virtual bool IsOk() const
+    {
+        // the cast here is safe because the derived classes always create
+        // wxGDIRefData objects
+        return m_refData && static_cast<wxGDIRefData *>(m_refData)->IsOk();
+    }
+
+    // don't use in the new code, use IsOk() instead
     bool IsNull() const { return m_refData == NULL; }
 
-    // older version, for backwards compat
+    // older version, for backwards compatibility only (but not deprecated
+    // because it's still widely used)
     bool Ok() const { return IsOk(); }
-    
-    virtual bool IsOk() const { return (m_refData != NULL) ; }
 
-#if defined(__WXMSW__) || defined(__WXPM__) || defined(__WXPALMOS__)
+#if defined(__WXMSW__) || defined(__WXPM__)
     // Creates the resource
     virtual bool RealizeResource() { return false; }
 
@@ -49,8 +70,24 @@ public:
     virtual WXHANDLE GetResourceHandle() const { return 0; }
 #endif // defined(__WXMSW__) || defined(__WXPM__)
 
+protected:
+    // replace base class functions using wxObjectRefData with our own which
+    // use wxGDIRefData to ensure that we always work with data objects of the
+    // correct type (i.e. derived from wxGDIRefData)
+    virtual wxObjectRefData *CreateRefData() const
+    {
+        return CreateGDIRefData();
+    }
+
+    virtual wxObjectRefData *CloneRefData(const wxObjectRefData *data) const
+    {
+        return CloneGDIRefData(static_cast<const wxGDIRefData *>(data));
+    }
+
+    virtual wxGDIRefData *CreateGDIRefData() const = 0;
+    virtual wxGDIRefData *CloneGDIRefData(const wxGDIRefData *data) const = 0;
+
     DECLARE_DYNAMIC_CLASS(wxGDIObject)
 };
 
-#endif
-    // _WX_GDIOBJ_H_BASE_
+#endif // _WX_GDIOBJ_H_BASE_