So why don't you split this single method into three methods (open tag, write contents, close tag) just like the stream writer does? Possibly even with a way to allow the parent class to append attributes to the opening tag created by the child class using writeAttributes. This should work:
Qt Code: 
  1. class Object {
  2. public:
  3. virtual void serialize(XmlStreamWriter &writer) {
  4.   openTag(writer);
  5.   writeContents(writer);
  6.   closeTag(writer);
  7. }
  8. protected:
  9.   virtual void openTag(XmlStreamWriter &writer, bool open = true) {}
  10.   virtual void closeTag(XmlStreamWriter &writer) { writer.writeEndElement();}
  11.   virtual void writeContents(XmlStreamWriter &writer) {}
  12. };
  13.  
  14. class SubObject : public Object {
  15. protected:
  16.   virtual void openTag(XmlStreamWriter &writer, bool open = true) {
  17.     if(open) { stream.writeStartElement(...); }
  18.     writer.writeAttribute(...);
  19.     Object::openTag(writer, false); // pass false to mark the parent should not open the tag by itself
  20.   }
  21.   virtual void closeTag(XmlStreamWriter &writer) {
  22.     // this should work the other way round, the top-most class should close the tag
  23.     writer....
  24.     Object::closeTag(writer);
  25.   }
  26.   virtual void writeContents(XmlStreamWriter &writer) {
  27.     Object::writeContents(writer);
  28.     writer...
  29.   }
  30. };
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