TXMLDocument 'Invalid pointer operation' when freeing

Question

I'm using the TXMLDocument to write an XML string which is used in a web server. The component is created when the server receives the request, produces XML, passes it back to the client, then the component is free'd. However, when this component is free'd, I get Invalid pointer operation.

  XML:= TXMLDocument.Create(nil);
  try
    XML.Active:= True;
    nRoot:= XML.AddChild('topics');
    for X := 0 to FCHM.Topics.Count - 1 do begin
      nTopic:= nRoot.AddChild('topic');
      //Add more data...

    end;
    Response.ContentText:= XML.XML.Text;
    Response.ContentType:= 'text/xml';
    XML.Active:= False;
  finally
    XML.Free; //<-- Invalid pointer operation
  end;

Why am I getting this and how do I get rid of it?

Strangely, although I can confirm that Response.ContentText did in fact get the XML, for some reason the web server fails to return this data back to the client after this exception - but I'm assuming that's a different cause/effect issue.

PS - CoInitialize(nil) and CoUninitialize are called around this handler since the web server is multi-threaded and the TXMLDocument is COM.

Answer 1

It's stated in the constructor's reference:

TXMLDocument components that are created at runtime without an owner are freed automatically when all references to their IXMLDocument interface are released.

Since you've specified no Owner in your TXMLDocument constructor call, you should not release it by yourself.