how to open snackbar as function in flutter code example

Example 1: flutter snackbar showing error

You can show material design snackbars using the following code:

Scaffold.of(context).showSnackBar(SnackBar(
      content: Text("New Notification"),
    ));
 
In some cases, this will throw an error and it can be resolved using a workaround:

//Declare a GlobalKey
GlobalKey _scaffoldKey = GlobalKey();

//Assing this key to the scaffold
Scaffold(
  key: _scaffoldKey,
  body: ...
)

//finally in the topmost code use this key in the following way
_scaffoldKey.showSnackBar(SnackBar(
      content: Text("New Notification"),
    ));

Example 2: flutter snackbar

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State {

  final GlobalKey _scaffoldKey = new GlobalKey();

  @override
  void initState() {
    super.initState();
    showInSnackBar("Some text");
  }

  @override
  Widget build(BuildContext context) {
    return new Padding(
            key: _scaffoldKey,
            padding: const EdgeInsets.all(16.0),
            child: new Text("Simple Text")
    );
  }

  void showInSnackBar(String value) {
    _scaffoldKey.currentState.showSnackBar(new SnackBar(
        content: new Text(value)
    ));
  }
}