flutter snackbar duration

final snackBar = SnackBar(content: Text('Yay! A SnackBar!'));

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

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