Enumerating DOM nodes in TChromium - delphi

Question

I am trying to enumerate DOM nodes using the following code (under XE2).
I have borrowed most of this from answers given here in SO, but for some reason it's not doing anything.
IOW, ProcessDOM() is not ever getting called.
And, I am at my wits end.
Could someone show me what I am doing wrong here.
Thanks in advance.
procedure ProcessNode(ANode: ICefDomNode);
var
Node1: ICefDomNode;
begin
if Assigned(ANode) then begin
Node1 := ANode.FirstChild;
while Assigned(Node1) do begin
{Do stuff with node}
ProcessNode(Node1);
Node1 := Node1.NextSibling;
end;
end;
end;
procedure ProcessDOM(const ADocument: ICefDomDocument);
begin
ProcessNode(ADocument.Body);
end;
procedure TMainForm.Chrome1LoadEnd(Sender: TObject; const ABrowser: ICefABrowser; const AFrame: ICefAFrame; AStatus: Integer);
begin
if Assigned(AFrame) then AFrame.VisitDomProc(ProcessDOM);
end;

Answer 1

I had the same problem and I used the demo guiclient it comes with dcef3. With the following it works.
type TCustomRenderProcessHandler = class(TCefRenderProcessHandlerOwn)
protected
function OnProcessMessageReceived(const browser: ICefBrowser; sourceProcess: TCefProcessId; const message: ICefProcessMessage): Boolean; override;
end;
Chromium1.browser.SendProcessMessage(PID_RENDERER, TCefProcessMessageRef.New('visitdom'));
function TCustomRenderProcessHandler.OnProcessMessageReceived(browser: ICefBrowser; sourceProcess: TCefProcessId; message: ICefProcessMessage): Boolean;
begin
if (message.Name = 'visitdom') then begin
browser.MainFrame.VisitDomProc(
procedure(const doc: ICefDomDocument)
begin
ProcessNode(Doc.Body);
end);
Result := True;
end;
end;
initialization
CefRenderProcessHandler := TCustomRenderProcessHandler.Create;

Answer 2

You need to add a procedure to the handler.
procedure ProcessNode(ANode: ICefDomNode);
Read this: 1

Answer 3

As this blog point out, The main difficulty when accessing a rendered page's DOM is that you can only do so in the same process as the associated renderer for that page.
You can't access dom from browser thread, you have to do it in renderer thread.
First, Forward a message (like visitdom) from browser process to rendering process
procedure TMainForm.crmLoadEnd(Sender: TObject; const browser: ICefBrowser;
const frame: ICefFrame; httpStatusCode: Integer);
var
msg : ICefProcessMessage;
begin
if IsMain(browser, frame) then
FLoading := False;
msg := TCefProcessMessageRef.New('visitdom');
browser.SendProcessMessage(PID_RENDERER, msg);
end;
Second, create a TCustomRenderProcessHandler to handle the message, send the result back to the browser processs.
function TCustomRenderProcessHandler.OnProcessMessageReceived(
const browser: ICefBrowser; sourceProcess: TCefProcessId;
const message: ICefProcessMessage): Boolean;
begin
Result := False;
if (message.Name = 'visitdom') then
begin
browser.MainFrame.VisitDomProc(
procedure(const doc: ICefDomDocument)
function ProcessNode(ANode: ICefDomNode) : String;
var
Node: ICefDomNode;
begin
Result := 'Not Found';
if Assigned(ANode) then
begin
Node := ANode.FirstChild;
while Assigned(Node) do
begin
if Node.ElementTagName='DIV' then
begin
if Node.GetElementAttribute('class')='tv-panels' then
begin
Result := 'Found';
Exit;
end;
end;
ProcessNode(Node);
Node := Node.NextSibling;
end;
end;
end;
var msg : ICefProcessMessage;
begin
msg := TCefProcessMessageRef.New('visitdom');
msg.ArgumentList.SetString(0, processNode(doc.Body));
browser.SendProcessMessage(PID_BROWSER, msg);
end);
Result := True;
end;
end;
Third, On browser process, create an handler to process the messenage sent back from render process.
procedure TMainForm.crmProcessMessageReceived(Sender: TObject;
const browser: ICefBrowser; sourceProcess: TCefProcessId;
const message: ICefProcessMessage; out Result: Boolean);
begin
Result := False;
if (message.Name = 'visitdom') then
begin
StatusBar.SimpleText := message.ArgumentList.GetString(0);
Result := True;
end;
end;
Be careful, while debuging, placing a breakpoint in rendering process never work. It will never reached there.