Check out example codes for "how to show snackbar in flutter". It will help you in understanding the concepts better.

Code Example 1

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<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

//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"),
    ));

Code Example 2

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<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

//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"),
    ));

Code Example 3

final snackBar = SnackBar(
  content: Text('Yay! A SnackBar!'),
  action: SnackBarAction(
    label: 'Undo',
    onPressed: () {
      // Some code to undo the change.
    },
  ),
);

 // Find the Scaffold in the widget tree and use
 // it to show a SnackBar.
 Scaffold.of(context).showSnackBar(snackBar);

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