function OpenFileDialogCallBack(Wnd: HWND; uMsg: UINT; wParam: WPARAM;
  lParam: LPARAM): UINT; stdcall;
var
  OpenFileNotify: LPOFNOTIFY;
  OpenFileName: Windows.POPENFILENAME;
  DialogRec: POpenFileDialogRec;

  procedure Reposition(ADialogWnd: Handle);
  var
    Left, Top: Integer;
    ABounds, DialogRect: TRect;
  begin
    // Btw, setting width and height of dialog doesnot reposition child controls :(
    // So no way to set another height and width at least here

    if (GetParent(ADialogWnd) = Win32WidgetSet.AppHandle) then
    begin
      if Screen.ActiveCustomForm <> nil then
        ABounds := Screen.ActiveCustomForm.Monitor.BoundsRect
      else
      if Application.MainForm <> nil then
        ABounds := Application.MainForm.Monitor.BoundsRect
      else
        ABounds := Screen.PrimaryMonitor.BoundsRect;
    end
    else
      ABounds := Screen.MonitorFromWindow(GetParent(ADialogWnd)).BoundsRect;
    GetWindowRect(ADialogWnd, @DialogRect);
    Left := (ABounds.Right - DialogRect.Right + DialogRect.Left) div 2;
    Top := (ABounds.Bottom - DialogRect.Bottom + DialogRect.Top) div 2;
    SetWindowPos(ADialogWnd, HWND_TOP, Left, Top, 0, 0, SWP_NOSIZE);
  end;

  procedure ExtractDataFromNotify();
  begin
    OpenFileName := OpenFileNotify^.lpOFN;
    DialogRec := POpenFileDialogRec(OpenFileName^.lCustData);
    UpdateStorage(Wnd, OpenFileName);
    UpdateFileProperties(OpenFileName);
  end;
begin
  if uMsg = WM_INITDIALOG then
  begin
    // Windows asks us to initialize dialog. At this moment controls are not
    // arranged and this is that moment when we should set bounds of our dialog
    Reposition(GetParent(Wnd));
  end
  else
  if uMsg = WM_NOTIFY then
  begin
    OpenFileNotify := LPOFNOTIFY(lParam);
    if OpenFileNotify = nil then
      Exit;

    case OpenFileNotify^.hdr.code of
      CDN_INITDONE:
      begin
        ExtractDataFromNotify();
        TOpenDialog(DialogRec^.Dialog).DoShow;
      end;
      CDN_SELCHANGE:
      begin
        ExtractDataFromNotify();
        TOpenDialog(DialogRec^.Dialog).DoSelectionChange;
      end;
      CDN_FOLDERCHANGE:
      begin
        ExtractDataFromNotify();
        TOpenDialog(DialogRec^.Dialog).DoFolderChange;
      end;
      CDN_TYPECHANGE:
      begin
        ExtractDataFromNotify();
        DialogRec^.Dialog.IntfFileTypeChanged(OpenFileNotify^.lpOFN^.nFilterIndex);
      end;
    end;
  end;
  Result := 0;
end;