How can I get an IXMLNodeList from an XPath selection?

Question

I came across a question about XPath and Delphi TXmlDocument.

While the answer works fine for selecting a single xml node, I wanted to use it to select a list of nodes.

I found a similar utility function that is supposed to do exactly that, but it does not work correctly.

The apparently buggy function:

uses
  Xml.Xmldom, Xml.XMLIntf, Xml.XMLDoc;

function SelectNodes(xnRoot: IXmlNode; const nodePath: WideString): IXMLNodeList;
var
  intfSelect : IDomNodeSelect;
  intfAccess : IXmlNodeAccess;
  dnlResult  : IDomNodeList;
  intfDocAccess : IXmlDocumentAccess;
  doc: TXmlDocument;
  i : Integer;
  dn : IDomNode;
begin
  Result := nil;
  if not Assigned(xnRoot)
    or not Supports(xnRoot, IXmlNodeAccess, intfAccess)
    or not Supports(xnRoot.DOMNode, IDomNodeSelect, intfSelect) then
    Exit;

  dnlResult := intfSelect.selectNodes(nodePath);
  if Assigned(dnlResult) then
  begin
    Result := TXmlNodeList.Create(intfAccess.GetNodeObject, '', nil);
    if Supports(xnRoot.OwnerDocument, IXmlDocumentAccess, intfDocAccess) then
      doc := intfDocAccess.DocumentObject
    else
      doc := nil;

    for i := 0 to dnlResult.length - 1 do
    begin
      dn := dnlResult.item[i];
      Result.Add(TXmlNode.Create(dn, nil, doc));
    end;
  end;
end;

A simplified version that does not use a IXMLNodeList, but the "raw" IDomNodeList instead:

function SimpleSelectNodes(xnRoot: IXmlNode; const nodePath: WideString): IDOMNodeList;
var
  intfSelect : IDomNodeSelect;
begin
  Result := nil;
  if not Assigned(xnRoot)
    or not Supports(xnRoot.DOMNode, IDomNodeSelect, intfSelect) then
    Exit;

  Result := intfSelect.selectNodes(nodePath);
end;

Test code:

procedure TForm1.FormCreate(Sender: TObject);
var
  Doc: IXMLDocument;
  Root: IXMLNode;
  DomNodeList: IDomNodeList;
  XmlNodeList: IXMLNodeList;
  XmlNode : IXMLNode;
  I: Integer;
begin
  // Build a test DOM tree in memory
  Doc := NewXMLDocument;
  Root := Doc.AddChild('root');
  Root.AddChild('C1');
  Root.AddChild('C2');
  Root.AddChild('C3');

  // Select using the IDomNodeList interface
  DomNodeList := SimpleSelectNodes(Root, '/root/*');
  for I := 0 to DomNodeList.length - 1 do
    ShowMessage(DomNodeList.item[I].nodeName);

  // Select using the IXMLNodeList interface
  XmlNodeList := SelectNodes(Root, '/root/*');
  XmlNode := XmlNodeList.First;
  while XmlNode <> nil do
  begin
    ShowMessage(XmlNode.NodeName);
    XmlNode := XmlNode.NextSibling;
  end;
end;

While the SimpleSelectNodes version works fine, the SelectNodes function does not.

It returns a IXMLNodeList, but when I try to actually iterate through this list I only get the first item, the NextSibling is nil.

How can I get the IXMLNodeList to work?

Answer 1

I had the same issue (with basically the same code).

The only way I could resolve it was to iterate through the nodes by index, as NextSibling returns nil for some reason every time. Something like this works:

var
  i: Integer;
  Nodes: IXMLNodeList;
  Node: IXMLNode;
begin
  Nodes := SelectNodes(...);
  for i := 0 to NodeList.Count - 1 do
  begin
    Node := NodeList.Nodes[i];
    // Process node
  end;
end;