如何为Flutter中的TextField，NumberFormat Exception提供默认值？

import 'package:flutter/material.dart';
import 'package:intl/intl.dart';

class MyTextField extends StatefulWidget {
  @override
  _MyTextFieldState createState() => _MyTextFieldState();
}

class _MyTextFieldState extends State<MyTextField> {
  TextEditingController _controller = TextEditingController();
  String _defaultValue = '0';

  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: _controller,
      decoration: InputDecoration(
        labelText: 'Enter a number',
      ),
      keyboardType: TextInputType.number,
      onChanged: (value) {
        setState(() {
          _defaultValue = value;
        });
      },
      onSubmitted: (value) {
        try {
          double number = NumberFormat.decimalPattern().parse(value);
          // 如果输入的值可以成功解析为数字，则更新默认值
          setState(() {
            _defaultValue = number.toString();
          });
        } catch (e) {
          // 如果出现NumberFormat Exception，则设置默认值为'0'
          setState(() {
            _defaultValue = '0';
          });
        }
      },
    );
  }
}