怎么查找一级节点、二级节点，并赋值？XML有关问题

如何查找一级节点、二级节点，并赋值？XML问题
例子如下
//更改
 xml->LoadFromFile("C:\\Sample.xml");
//这个位置以下  怎么查找一级节点？并赋值？
 _di_IXMLNode nodeupdate =xml->DocumentElement->ChildNodes->FindNode(ResultSet);
 nodeupdate->AttributeNodes->operator [](1)->NodeValue=(WideString)(5);
 xml->SaveToFile("Sample.xml");
[解决办法]

__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
        Button1->Visible= false;
}
//---------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    _di_IXMLDocument xml;
    WideString strXmlFile = "test.xml";

    if(FileExists(strXmlFile))
    {
        xml = LoadXMLDocument(strXmlFile);
        xml->Active = true;
        xml->Options = xml->Options << doNodeAutoIndent;//自动换行

        _di_IXMLNode root;
        root = xml->ChildNodes->FindNode("Machine")->ChildNodes->FindNode("LocalData")->ChildNodes->FindNode("paraModifyHs");

        _di_IXMLNode node;
        node = root->AddChild("Item");
        node->Attributes[WideString("name")] = WideString("4");
        node->Attributes[WideString("oldValue")] = WideString("4");
        node->Attributes[WideString("newValue")] = WideString("4");
        node->Attributes[WideString("modiyData")] = WideString(FormatDateTime( "YYYY/MM/DD ",Date()) + FormatDateTime( "hh:mm:ss",Time()));
        xml->SaveToFile(strXmlFile);
        xml->Active = false;
    }
    else
    {
        try
        {
            xml = NewXMLDocument();
            xml->Options = xml->Options << doNodeAutoIndent;
            xml->Encoding = L"GB2312";
            xml->AddChild("Machine");

            _di_IXMLNode root = xml->ChildNodes->FindNode("Machine");
            root->Attributes[WideString("machinetype")] = WideString("GD_H500");
            root->Attributes[WideString("address")] = WideString("5.4.36.211.1.1");
            root->Attributes[WideString("port")] = WideString("801");
            root->AddChild("LocalData"); 
 

            root = root->ChildNodes->FindNode("LocalData");
            root->AddChild("paraModifyHs");

            root = root->ChildNodes->FindNode("paraModifyHs");

            _di_IXMLNode node;
            node = root->AddChild("Item");
            node->Attributes[WideString("name")] = WideString("4");
            node->Attributes[WideString("oldValue")] = WideString("4");
            node->Attributes[WideString("newValue")] = WideString("4");
            node->Attributes[WideString("modiyData")] = WideString(FormatDateTime( "YYYY/MM/DD ",Date()) + FormatDateTime( "hh:mm:ss",Time()));

            xml->SaveToFile(strXmlFile);
            
            xml->Active = false;
        }
        catch(...)
        {
            xml->Active = false;
        }
    }
}
//---------------------------------------
void __fastcall TForm1::Button2Click(TObject *Sender)
{
    _di_IXMLDocument xml;
    WideString strXmlFile = "ParaModifyHistory.xml";

    if(FileExists(strXmlFile))
    {
        xml = LoadXMLDocument(strXmlFile);
        xml->Active = true;
        xml->Options = xml->Options << doNodeAutoIndent;//自动换行

        _di_IXMLNode root;
        root = xml->ChildNodes->FindNode("Machine")->ChildNodes->FindNode("LocalData")->ChildNodes->FindNode("paraModifyHs");

        _di_IXMLNode node;
        _di_IXMLNodeList list = root->ChildNodes;

        String modifyDate;
        SYSTEMTIME systemTime;
        GetLocalTime(&systemTime);

        TDateTime dt2 = SystemTimeToDateTime(systemTime);
        //dt2 = StrToDateTime("2011-08-02 15:53:09");

        TDateTime dt;


        for(int i = 0; i<list->Count; ++i)
        {
            String ss =  list->Nodes[i]->GetAttribute("modiyData"); 
 
            dt = StrToDateTime(list->Nodes[i]->GetAttribute("modiyData"));
            if(double(dt - dt2) > 30)
            {
                list->Delete(i);
                i = -1;
            }
        }
        xml->SaveToFile(strXmlFile);
        xml->Active = false;
    }
}
//---------------------------------------

void __fastcall TForm1::Button3Click(TObject *Sender)
{
        Button1->Visible =true;
        Button1->BringToFront();
}
//---------------------------------------