a transação não está aparecendo na minha lista de transferências

import 'package:flutter/material.dart';

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

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

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: '0000',
          ),
          Editor(
            controlador: _controladorCampoValor,
            rotulo: 'Valor',
            dica: '100.0',
            icone: Icons.monetization_on,
          ),
          RaisedButton(
            child: Text('Confirmar'),
            onPressed: () => _criaTransferencia(context),
          ),
        ],
      ),
    );
  }

  void _criaTransferencia(BuildContext context) {
    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('Criando transferência');
      debugPrint('$transferenciaCriada');
      Navigator.pop(context, 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 StatefulWidget {
  final List<Transferencia> _transferencias = List();

  @override
  State<StatefulWidget> createState() {
    return ListaTransferenciasState();
  }
}

class ListaTransferenciasState extends State<ListaTransferencias> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Transferências'),
      ),
      body: ListView.builder(
        itemCount: widget._transferencias.length,
        itemBuilder: (context, indice) {
          final transferencia = widget._transferencias[indice];
          return ItemTransferencia(transferencia);
        },
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () {
          final Future<Transferencia> future =
              Navigator.push(context, MaterialPageRoute(builder: (context) {
            return FormularioTransferencia();
          }));
          future.then((transferenciaRecebida) {
            debugPrint('Chegou no then do future');
            debugPrint('$transferenciaRecebida');
            widget._transferencias.add(transferenciaRecebida);
          });
        },
      ),
    );
  }
}

class ItemTransferencia extends StatelessWidget {
  final Transferencia _transferencia;

  ItemTransferencia(this._transferencia);

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Card(
      child: ListTile(
        leading: Icon(Icons.monetization_on),
        title: Text(_transferencia.valor.toString()),
        subtitle: Text(_transferencia.numeroConta.toString()),
      ),
    );
  }
}

class Transferencia {
  final double valor;
  final int numeroConta;

  Transferencia(this.valor, this.numeroConta);

  @override
  String toString() {
    return 'Transferencia{valor: $valor, numeroConta: $numeroConta}';
  }
}