Question

guys: I got a problem about “how to get an IHTMLElementCollection obj which composed of several IHTMLElements” in object-pascal programming , my codes below:

function TExDomUtils.GetElementsByClassName(vDoc:IHTMLDocument3; strClassName:string):IHTMLElementCollection;
var
  vElementsAll : IHTMLElementCollection;
  vElementsRet : IHTMLElementCollection;
  vElement : IHTMLElement;
  docTmp : IHTMLDocument2;
  I ,J: Integer;
begin
  J := 0;
  vElementsAll := vDoc.getElementsByTagName('*');
  for I:=0 to vElementsAll.length - 1 do
  begin
    vElement := vElementsAll.item(I,0) as IHTMLElement;
    if vElement.getAttribute('class',0) = strClassName then
    begin
      // how to get an IHTMLElementCollection obj which composed of several IHTMLElements?
      J := J + 1;
    end;

  end;

  Result := vElementsRet;
end;

Answer 1

You could simply create your own container class, such as TList<IHTMLElement> or an array of IHTMLElements:

type
  THTMLElements = array of IHTMLElement;

function GetElementsByClassName(ADoc: IDispatch; const strClassName: string): THTMLElements;
var
  vDocument: IHTMLDocument2;
  vElementsAll: IHTMLElementCollection;
  vElement: IHTMLElement;
  I, ElementCount: Integer;
begin
  Result := nil;
  ElementCount := 0;
  if not Supports(ADoc, IHTMLDocument2, vDocument) then
    raise Exception.Create('Invalid HTML document');
  vElementsAll := vDocument.all;
  SetLength(Result, vElementsAll.length); // set length to max elements
  for I := 0 to vElementsAll.length - 1 do
    if Supports(vElementsAll.item(I, EmptyParam), IHTMLElement, vElement) then
      if SameText(vElement.className, strClassName) then
      begin
        Result[ElementCount] := vElement;
        Inc(ElementCount);
      end;
  SetLength(Result, ElementCount); // adjust Result length
end;

Usage:

procedure TForm1.FormCreate(Sender: TObject);
begin
  WebBrowser1.Navigate('http://stackoverflow.com/questions/14535755/how-to-get-an-ihtmlelementcollection-obj-which-composed-of-several-ihtmlelements');
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  Elements: THTMLElements;
  I: Integer;
begin
  // show Tags information for SO page:
  Elements := GetElementsByClassName(WebBrowser1.Document, 'post-tag');
  ShowMessage(IntToStr(Length(Elements)));
  for I := 0 to Length(Elements) - 1 do
    Memo1.Lines.Add(Elements[I].innerHTML + ':' + Elements[I].getAttribute('href', 0));
end;

---

The main problem with returning the result as IHTMLElementCollection, is that IHTMLElementCollection is created internally by IHTMLDocument, and I could not find any way of creating a new instance of IHTMLElementCollection and adding references of the elements to it e.g.:

vElementsRet := CoHTMLElementCollection.Create as IHTMLElementCollection

will result Class not registered exception.