问:
 我想把字符串转换成stream,
 然后
 System.Xml.XmlTextReader xmlReader = new System.Xml.XmlTextReader(System.IO.Stream input)
______________________________________________________________________________________________
 答1:
 为何一定要转呢?
string xmlFrag ="<book> " +
                          "<title>Pride And Prejudice</title>" +
                          "<bk:genre>novel</bk:genre>" +
                          "</book>"; 
    //Create the XmlNamespaceManager.
     NameTable nt = new NameTable();
     XmlNamespaceManager nsmgr = new XmlNamespaceManager(nt);
     nsmgr.AddNamespace("bk", "urn:sample");
    //Create the XmlParserContext.
     XmlParserContext context = new XmlParserContext(null, nsmgr, null, XmlSpace.None);
    //Create the reader. 
     XmlTextReader reader = new XmlTextReader(xmlFrag, XmlNodeType.Element, context);