Get a list of strings from sharedpreferences

sharedpreferences().getnom.length;
//or
sharedpreferences().getnom[index];
//errors
//The getter 'length' isn't defined for the class 'Future<List<String>>'.
//Error: The operator '[]' isn't defined for the class 'Future<List<String>>'.

class sharedprefernces {
  List<String> _depto = [];
  List<String> _mun = [];
  List<String> _com = [];
  List<String> _nom = [];
  List<String> _peso = [];
  List<String> _qq = [];
  List<String> _varie = [];
  List<String> _date = [];
  List<String> _est = [];

  Future<List<String>> getnom() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  return prefs.getStringList('nom');
  }
}