subscription_widget_mvvm_build.dart

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Expanded(
          child: StreamBuilder<String>(
            stream: _viewModel.outputErrorText,
            builder: (context, snapshot) {
              return MyTextField(
                  controller: controller,
                  hintText: "Email",
                  errorText: snapshot.data);
            },
          ),
        ),
        StreamBuilder(
            stream: _viewModel.outputIsButtonEnabled,
            builder: (context, snapshot) {
              return SubmitButton(enabled: snapshot.data ?? false);
            }),
      ],
    );
  }