Scaffold.of() called with a context that does not contain a Scaffold

This exception happens because you are using the context of the widget that instantiated Scaffold. Not the context of a child of Scaffold.

You can solve this by just using a different context :

Scaffold(
    appBar: AppBar(
        title: Text('SnackBar Playground'),
    ),
    body: Builder(
        builder: (context) => 
            Center(
            child: RaisedButton(
            color: Colors.pink,
            textColor: Colors.white,
            onPressed: () => _displaySnackBar(context),
            child: Text('Display SnackBar'),
            ),
        ),
    ),
);

Note that while we’re using Builder here, this is not the only way to obtain a different BuildContext.

It is also possible to extract the subtree into a different Widget (usually using extract widget refactor)