type
  TFileOpenDialog = class(Dialogs.TFileOpenDialog)
  protected
    function SelectionChange: HRESULT; override;
  end;

implementation

{ TFileOpenDialog }

function TFileOpenDialog.SelectionChange: HRESULT;
var
  Attrs: DWORD;
  ShellItem: IShellItem;
begin
  Result := inherited;
  if Succeeded(Dialog.GetCurrentSelection(ShellItem)) and
    Succeeded(ShellItem.GetAttributes(SFGAO_FOLDER, Attrs)) and (Attrs = SFGAO_FOLDER) then
  begin
    // folder is selected
  end
  else
  begin
    // file is selected
  end;
end;