Como acrescentar o snackBar e componentizar ele para ser usado em qualquer parte do código

import 'package:flutter/material.dart';

void main() => runApp(BytebankApp());

class BytebankApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: FormularioTransferencia(),
      ),
    );
  }
}

class FormularioTransferencia extends StatelessWidget {
  final TextEditingController _controladorCampoNumeroConta =
      TextEditingController();
  final TextEditingController _controladorCampoValor = TextEditingController();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Criando Transferência'),
      ),
      body: Column(
        children: <Widget>[
          Editor(
            controlador: _controladorCampoNumeroConta,
            rotulo: 'Número da Conta',
            dica: '000',
          ),
          Editor(
            controlador: _controladorCampoValor,
            rotulo: 'Valor',
            dica: '0.00',
            icone: Icons.monetization_on,
          ),
          RaisedButton(
              child: Text('Confirmar'), onPressed: () => _criaTransferencia())
        ],
      ),
    );
  }

  void _criaTransferencia() {
    debugPrint('Clicou no botão');

    final int numeroConta = int.tryParse(_controladorCampoNumeroConta.text);
    final double valor = double.tryParse(_controladorCampoValor.text);
    if (numeroConta != null && valor != null) {
      final transferenciaCriada = Transferencia(valor, numeroConta);
      debugPrint('$transferenciaCriada');
    }
  }
}

class Editor extends StatelessWidget {
  final TextEditingController controlador;
  final String rotulo;
  final String dica;
  final IconData icone;

  Editor({this.controlador, this.rotulo, this.dica, this.icone});
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(16.0),
      child: TextField(
        controller: controlador,
        style: TextStyle(fontSize: 24.0),
        decoration: InputDecoration(
          icon: icone != null ? Icon(icone) : null,
          labelText: rotulo,
          hintText: dica,
        ),
        keyboardType: TextInputType.number,
      ),
    );
  }
}

class ListaTransferencias extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Transferências'),
      ),
      body: Column(
        children: <Widget>[
          ItemTransferencia(Transferencia(100, 231080)),
          ItemTransferencia(Transferencia(200, 231180)),
        ],
      ),
    );
  }
}

class ItemTransferencia extends StatelessWidget {
  final Transferencia _transferencia;

  ItemTransferencia(this._transferencia);
  @override
  Widget build(Object context) {
    return Card(
        child: ListTile(
      leading: Icon(Icons.monetization_on),
      title: Text(_transferencia.valor.toString()),
      subtitle: Text(_transferencia.conta.toString()),
    ));
  }
}

class Transferencia {
  final double valor;
  final int conta;
  Transferencia(this.valor, this.conta);
  @override
  String toString() {
    return 'Transferencia{valor: $valor,conta: $conta}';
  }
}