Question

I always get an access violation when I try to use the DocumentElement of the XMLDocument. I create XMLDocument based on the existence of some file.

Error message

Project project1.exe raised exception class EAccessViolation with
message ‘Access violation at address 0047B152 in module
‘project1.exe’.Read of Address B1D59357′

My code

unit XMLBase;

interface
uses
  SysUtils, xmldom, XMLIntf, XMLDoc, Forms;

type
  TXMLbase = class
  private
    { Private declarations }
  public
    XMLDocument1: TXMLDocument;
    root: IXMLNode;    
    constructor Create;
  end;

var
  fn: string;

implementation

constructor TXMLbase.Create;
begin   
  fn := ChangeFileExt(Application.ExeName, '.xml');
  XMLDocument1 := TXMLDocument.Create(nil);
  XMLDocument1.Options := [doNodeAutoIndent];
  XMLDocument1.Active := False;
  //optional, is used to indent the Xml document
  if FileExists(fn) then
  begin
  XMLDocument1.LoadFromFile(fn);
  XMLDocument1.Active:= True;
  root := XMLDocument1.DocumentElement;  //<<--- Access Voilation
  end
  else
  begin
    XMLDocument1.Active := False;
    XMLDocument1.XML.Text := '';
    XMLDocument1.Active := True;
    root := XMLDocument1.AddChild('Settings');    
  end;
XMLDocument1.SaveToFile(fn);
end;

end.

Access violations arise due to improper initialization of object or pointers, does that mean that the XMLDocument is not being initialized?

Answer 1

As indicated by David just changing your XMLDocument1 declaration from XMLDocument1: TXMLDocument to XMLDocument1: IXMLDocument solves the problem. Your issue is related to Using TXmlDocument