有没有一种方法可以跟踪自对话消息在Flutter中消失以来的天数？

dependencies:
  shared_preferences: ^2.0.8

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

class MessageTracker {
  static const String _keyLastMessageDate = 'last_message_date';

  Future<int> getDaysSinceLastMessage() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    DateTime lastMessageDate = DateTime.parse(prefs.getString(_keyLastMessageDate) ?? '');
    DateTime currentDate = DateTime.now();
    int days = currentDate.difference(lastMessageDate).inDays;
    return days;
  }

  Future<void> updateLastMessageDate() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    DateTime currentDate = DateTime.now();
    prefs.setString(_keyLastMessageDate, currentDate.toString());
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  final MessageTracker messageTracker = MessageTracker();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Message Tracker'),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              ElevatedButton(
                child: Text('Update Last Message Date'),
                onPressed: () {
                  messageTracker.updateLastMessageDate();
                },
              ),
              FutureBuilder<int>(
                future: messageTracker.getDaysSinceLastMessage(),
                builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
                  if (snapshot.hasData) {
                    return Text('Days since last message: ${snapshot.data}');
                  } else {
                    return Text('Loading...');
                  }
                },
              ),
            ],
          ),
        ),
      ),
    );
  }
}