I'm creating an instance of TXMLDocument at runtime, to load and parse a XML file. You can check the code below:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, xmldom, XMLIntf, msxmldom, XMLDoc, StdCtrls;
type
Txml = class(TForm)
// XMLDocument1: TXMLDocument;
Memo1: TMemo;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
xml: Txml;
implementation
{$R *.dfm}
procedure Txml.FormCreate(Sender: TObject);
var i,j:integer;
aNode:IXMLNode;
ws:String;
XMLDocument1:TXMLDocument;
begin
Memo1.Lines.Clear;
XMLDocument1 := TXMLDocument.Create(nil);
try
XMLDocument1.LoadFromFile('C:\a.xml');
XMLDocument1.Active := true;
aNode := XMLDocument1.ChildNodes.First;
while aNode<>nil do
begin
for i := 0 to aNode.ChildNodes.Count-1 do
begin
if aNode.ChildNodes[i].NodeName = 'Role' then
begin
Memo1.Lines.Add('Tag - '+aNode.ChildNodes[i].ChildNodes['Tag'].Text);
for j := 0 to aNode.ChildNodes[i].ChildNodes.Count-1 do
if aNode.ChildNodes[i].ChildNodes[j].HasChildNodes then
begin
ws := VarToStr(aNode.ChildNodes[i].ChildNodes[j].ChildValues['Tag']);
if trim(ws)<>'' then
Memo1.Lines.Add(ws);
ws := VarToStr(aNode.ChildNodes[i].ChildNodes[j].ChildValues['Value']);
if trim(ws)<>'' then
Memo1.Lines.Add(ws);
end;
end;
end;
aNode := aNode.NextSibling;
end;
XMLDocument1.Active := false;
finally
FreeAndNil(XMLDocument1);
end;
end;
end.
The problem is that this is generating an AV. As you probably have seen, before the component was on the form (// XMLDocument1: TXMLDocument;).
Why when the component was on the form the code was working, but when I'm creating it at run-time it generates AV?
LE: solution: based on the answers/comments and Delphi Help:
XMLDocument1 : IXMLDocument; //not TXMLDocument
XMLDocument1 := LoadXMLDocument(...);
FreeAndNil;// must be deleted
From what I know you should be using interface IDoc: IXMLDocument;
instead.
From docs:
When TXMLDocument is created without an Owner, it behaves like an interfaced object. That is, when all references to its interface are released, the TXMLDocument instance is automatically freed. When TXMLDocument is created with an Owner, however, it behaves like any other component, and is freed by its Owner.
In other words, when creating a TXMLDocument
instance with a nil
Owner, do not call Free()
or FreeAndNil()
on the instance, and you must assign the object to an IXMLDocument
variable so its now-active reference count is managed properly.