extracting_widget.dart

RoundedButton(Colors.cyan,
                () => Navigator.pushNamed(context, LoginScreen.id), 'Login'),
            RoundedButton(
                Colors.blueAccent,
                () => Navigator.pushNamed(context, RegistrationScreen.id),
                'Register')
          ],
        ),
      ),
    );
  }
}

class RoundedButton extends StatelessWidget {
  RoundedButton(this.colour, @required this.onPressed, this.text);

  final Color colour;
  final String text;
  final Function onPressed;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.symmetric(vertical: 16.0),
      child: Material(
        elevation: 5.0,
        color: colour,
        borderRadius: BorderRadius.circular(30.0),
        child: MaterialButton(
            onPressed: () {
              //Go to login screen.
              // Navigator.pushNamed(context, LoginScreen.id);
              onPressed();
            },
            minWidth: 200.0,
            height: 42.0,
            child: Text(text)),
      ),
    );
  }
}