Hàm show thông báo ra màn hình trong flutter

void showInSnackBar(String value) {
  _scaffoldKey.currentState.showSnackBar(new SnackBar(
    content: new Text(value),
    duration: new Duration(milliseconds: 700),
  ));
}

+ Bổ sung : 

@override
 Widget build(BuildContext context) {
  return new Scaffold(
    key: _scaffoldKey,
    body: new SafeArea(