我无法显示来自json文件Flutter的数据

class User {
  final String name;
  final int age;
  final String email;

  User({required this.name, required this.age, required this.email});

  factory User.fromJson(Map<String, dynamic> json) {
    return User(
      name: json['name'],
      age: json['age'],
      email: json['email'],
    );
  }
}

import 'dart:convert';

import 'package:flutter/material.dart';

class MyPage extends StatefulWidget {
  @override
  _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
  late User user;

  @override
  void initState() {
    super.initState();
    // 这里假设你已经获取到了jsonString，可以从文件或网络中获取
    String jsonString = '{"name": "John Doe","age": 25,"email": "johndoe@example.com"}';
    final jsonMap = json.decode(jsonString);
    user = User.fromJson(jsonMap);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('JSON数据显示示例'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('Name: ${user.name}'),
            Text('Age: ${user.age.toString()}'),
            Text('Email: ${user.email}'),
          ],
        ),
      ),
    );
  }
}