为什么Node.ChildNodes.FindNode()失败而Node.ChildNodes[]成功？

Question

有人能解释一下为什么 ChildNodes.FindNode('')（1）会失败，而 ChildNodes['']（2）却成功吗？==>

代码：

const
   cNodeSOAPEnvelope  = 's:Envelope';
   cNodeSOAPBody      = 's:Body';
   cNodeSOAPBodyFault = 's:Fault';
   cNodeSOAPHeader    = 's:Header';
   cNodeFaultCode     = 'faultcode';
   cNodeFaultString   = 'faultstring';

procedure TFrmXMLParsingTests.BtnTestClick(Sender: TObject);
var
   SoapBodyNode,
   SoapBodyFaultNode,
   SoapHeaderNode,
   FaultCodeNode,
   FaultTextNode,
   RootNode: IXmlNode;
begin
   RootNode := XMLDoc.DocumentElement;
   Assert(RootNode.NodeName = cNodeSOAPEnvelope,'Root node is not SOAP envelope');
   SoapBodyNode := RootNode.ChildNodes[cNodeSOAPBody];
   SoapBodyFaultNode := SoapBodyNode.ChildNodes[cNodeSOAPBodyFault];
   if SoapBodyFaultNode <> nil then
   begin
//      FaultCodeNode := SoapBodyFaultNode.ChildNodes.FindNode(cNodeFaultCode);     (*1*)
//      FaultTextNode := SoapBodyFaultNode.ChildNodes.FindNode(cNodeFaultString);   (*1*)
      FaultCodeNode := SoapBodyFaultNode.ChildNodes[cNodeFaultCode];                (*2*) 
      FaultTextNode := SoapBodyFaultNode.ChildNodes[cNodeFaultString];              (*2*) 
      Exit; // Nothing more to do
   end; { fault in body }
   SoapHeaderNode := RootNode.ChildNodes.FindNode(cNodeSOAPHeader);
   Assert(SoapHeaderNode <> nil,'SOAP Header not found');
end;

XML:

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
   <s:Body>
      <s:Fault>
         <faultcode xmlns:a="http://schemas.microsoft.com/exchange/services/2006/types">a:ErrorSchemaValidation</faultcode>
         <faultstring xml:lang="nl-NL">The [snip] value.</faultstring>
         <detail>
            <e:ResponseCode xmlns:e="http://schemas.microsoft.com/exchange/services/2006/errors">ErrorSchemaValidation</e:ResponseCode>
            <e:Message xmlns:e="http://schemas.microsoft.com/exchange/services/2006/errors">The request failed schema validation.</e:Message>
            <t:MessageXml xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
               <t:LineNumber>10</t:LineNumber>
               <t:LinePosition>30</t:LinePosition>
               <t:Violation>The [snip] value.</t:Violation>
            </t:MessageXml>
         </detail>
      </s:Fault>
   </s:Body>
</s:Envelope>

感谢
Jan

- Jan Doggen

---

GetNode() 调用 XMLDoc.pas 中的 FindNode()。你使用哪个 DOM 供应商/解析器？ - NGLN

@NGLN 默认的 Microsoft (MSXLM 如果我没记错) - Jan Doggen

Answer 1

阅读文档。当您访问ChildNodes[]属性请求不存在的节点时，如果父XMLDocument的Options属性启用了doNodeAutoCreate标志，则会自动创建新节点，否则将引发EXMLDocError异常。

更新：由于您的文档中包含多个XML命名空间，因此在使用ChildNodes[]属性和FindNode()方法时需要考虑命名空间。您的代码无法正确找到<faultcode>和<faultstring>节点的原因是它们具有不同的命名空间（实际上，它们根本没有任何命名空间），而ChildNodes[]属性和1参数的FindNode()方法期望它们具有与其父节点相同的命名空间。当您搜索具有不同命名空间的子节点的命名空间节点时，必须在搜索中包括子节点的命名空间才能正确找到子节点。

尝试这个：

uses
  ..., XmlIntf, XMLDom, XmlDoc;

const
  cSoapEnvelopeNS    = 'http://schemas.xmlsoap.org/soap/envelope/';
  cExchangeErrorsNS  = 'http://schemas.microsoft.com/exchange/services/2006/errors';
  cExchangeTypesNS   = 'http://schemas.microsoft.com/exchange/services/2006/types';

  cNodeSOAPEnvelope  = 'Envelope';
  cNodeSOAPBody      = 'Body';
  cNodeSOAPBodyFault = 'Fault';
  cNodeSOAPHeader    = 'Header';
  cNodeFaultCode     = 'faultcode';
  cNodeFaultString   = 'faultstring';
  cNodeDetail        = 'detail';
  cNodeResponseCode  = 'ResponseCode';
  cNodeMessage       = 'Message';
  cNodeMessageXml    = 'MessageXml';
  cNodeLineNumber    = 'LineNumber';
  cNodeLinePosition  = 'LinePosition';
  cNodeViolation     = 'Violation';

procedure TFrmXMLParsingTests.BtnTestClick(Sender: TObject);
var
   RootNode,
   SoapBodyNode,
   SoapBodyFaultNode,
   SoapHeaderNode,
   FaultCodeNode,
   FaultTextNode,
   DetailNode,
   ResponseCodeNode,
   MessageNode,
   MessageXmlNode,
   LineNumberNode,
   LinePositionNode,
   ViolationNode: IXMLNode;
begin
   RootNode := XMLDoc.DocumentElement;
   Assert(NodeMatches(RootNode.DOMNode, cNodeSOAPEnvelope, cSoapEnvelopeNS), 'Root node is not SOAP envelope');

   // these have the same namespace as <Envelope>
   SoapBodyNode := RootNode.ChildNodes[cNodeSOAPBody];
   SoapBodyFaultNode := SoapBodyNode.ChildNodes.FindNode(cNodeSOAPBodyFault);

   if SoapBodyFaultNode <> nil then
   begin
      // these have a different namespace than <Fault>!
      FaultCodeNode := SoapBodyFaultNode.ChildNodes.FindNode(cNodeFaultCode, '');
      FaultTextNode := SoapBodyFaultNode.ChildNodes.FindNode(cNodeFaultString, '');
      DetailNode := SoapBodyFaultNode.ChildNodes.FindNode(cNodeDetail, '');

      if DetailNode <> nil then
      begin
        // these have different namespaces than <detail>!
        ResponseCodeNode := DetailNode.ChildNodes.FindNode(cNodeResponseCode, cExchangeErrorsNS);
        MessageNode := DetailNode.ChildNodes.FindNode(cNodeMessage, cExchangeErrorsNS);
        MessageXmlNode := DetailNode.ChildNodes.FindNode(cNodeMessageXml, cExchangeTypesNS);

        if MessageXmlNode <> nil then
        begin
          // these have the same namespace as <MessageXml>
          LineNumberNode := MessageXmlNode.ChildNodes.FindNode(cNodeLineNumber);
          LinePositionNode := MessageXmlNode.ChildNodes.FindNode(cNodeLinePosition);
          ViolationNode := MessageXmlNode.ChildNodes.FindNode(cNodeViolation);
        end;
      end;
      Exit;
   end;

   // this has the same namespace as <Envelope>
   SoapHeaderNode := RootNode.ChildNodes.FindNode(cNodeSOAPHeader);
   Assert(SoapHeaderNode <> nil,'SOAP Header not found');
end;

- Remy Lebeau

---

是的，我在源代码中看到了，但 OP 有节点，不是吗？ - NGLN

@Remy：哎呀，我忽略了那个 - 很危险。在NGLN：很可能ChildNode[]创建了FindNode()找不到的其他节点 - 我回到办公室后会检查一下。 - Jan Doggen

当正确使用时，FindNode()可以正常工作，但是您没有考虑XML命名空间，即使在XML文档中有多个命名空间。FindNode()有一个重载版本，它有第二个参数用于命名空间输入。 - Remy Lebeau

我更新了我的答案，包括一个使用命名空间节点的示例。 - Remy Lebeau

感谢Remy！我正在从头开始构建这个东西，希望能避免命名空间。你的示例代码使我节省了一个小时... - Jan Doggen

注意：doNodeAutoCreate默认为T/IXMLDocument选项，因此：XMLDoc.Options：= XMLDoc.Options- [doNodeAutoCreate]; - Jan Doggen

Answer 2

编写您自己的函数：

function SearchChilds(StartNode: IXMLNode; Nodename: string): IXMLnode;
var i: Integer;
begin
   Result := nil;
   for i := 0 to StartNode.ChildNodes.Count-1 do
   begin
      if (StartNode.ChildNodes[i] <> nil) and (StartNode.ChildNodes[i].LocalName = Nodename) then
      begin
         Result := StartNode.ChildNodes[i];
         break;
      end;
      if StartNode.ChildNodes[i].HasChildNodes then
      begin
         Result := SearchChilds(StartNode.ChildNodes[i], Nodename);
         if Result<>nil then break;
      end;
   end;
end;

- Wchris