xmldocument动态创建不能成功读出数据？该如何解决

xmldocument动态创建不能成功读出数据？
拖个XmlDocument1控件到窗口然后调用如下代码就能成功

C/C++ code

    XMLDocument1->LoadFromFile("C:\\mms.xml");    XMLDocument1->Active=true;    ShowMessage(AnsiString (XMLDocument1->DocumentElement->ChildNodes->Nodes[0]->Text));

C/C++ code

    TXMLDocument *XMLDocument1;    XMLDocument1=new TXMLDocument("C:\\mms.xml");    XMLDocument1->Active=true;    ShowMessage(AnsiString (XMLDocument1->DocumentElement->ChildNodes->Nodes[0]->Text));

C/C++ code

_di_IXMLDocument xml = LoadXMLDocument(WideString("C:\\mms.xml"));xml->Active = true;ShowMessage(AnsiString(xml->DocumentElement->ChildNodes->Nodes[0]->Text));