如何在Flutter中实现按日期重复的集市日通知功能

一、核心：集市日计算逻辑 #

首先需要确定一个基准集市日（首次打开APP时可让用户选择最近的一次集市日，或者预设小镇的固定起始日），之后每3天循环推算。核心代码逻辑如下：

// 计算下一个（或当前）集市日
DateTime calculateNextMarketDay(DateTime baseMarketDay, DateTime currentDate) {
  DateTime nextMarket = baseMarketDay;
  // 若基准日在当前日期之前，循环加3天直到找到最近的未来/当天日期
  while (nextMarket.isBefore(currentDate)) {
    nextMarket = nextMarket.add(const Duration(days: 3));
  }
  return nextMarket;
}

把基准日存在本地避免重复设置，用SharedPreferences实现：

// 保存基准日
void saveBaseMarketDay(DateTime date) async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  await prefs.setInt('base_market_day', date.millisecondsSinceEpoch);
}

// 获取基准日
Future<DateTime?> getBaseMarketDay() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  int? timestamp = prefs.getInt('base_market_day');
  return timestamp != null ? DateTime.fromMillisecondsSinceEpoch(timestamp) : null;
}

二、本地通知实现 #

用flutter_local_notifications库完成通知功能，步骤如下：

1. 初始化通知插件

final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
    FlutterLocalNotificationsPlugin();

// 初始化配置
Future<void> initNotifications() async {
  const AndroidInitializationSettings androidSettings =
      AndroidInitializationSettings('@mipmap/ic_launcher');
  const InitializationSettings initSettings =
      InitializationSettings(android: androidSettings);
  await flutterLocalNotificationsPlugin.initialize(initSettings);
}

2. 请求通知权限
   用户勾选checkbox时先申请权限：

Future<bool> requestNotificationPermission() async {
  if (Platform.isAndroid) {
    AndroidFlutterLocalNotificationsPlugin androidPlugin =
        flutterLocalNotificationsPlugin.resolvePlatformSpecificImplementation<AndroidFlutterLocalNotificationsPlugin>()!;
    return await androidPlugin.requestNotificationsPermission();
  }
  // iOS 权限请求逻辑可按需添加
  return true;
}

3. 设置定时通知
   开启通知后，计算触发时间（比如集市日当天早8点）并设置定时任务：

Future<void> scheduleMarketNotification(DateTime marketDay) async {
  // 设定通知触发时间为集市日当天8:00
  DateTime notifyTime = DateTime(
    marketDay.year,
    marketDay.month,
    marketDay.day,
    8,
    0,
  );

  const AndroidNotificationDetails androidDetails = AndroidNotificationDetails(
    'market_notify_channel',
    '集市日提醒',
    channelDescription: '提醒你即将到来的集市日',
    importance: Importance.high,
    priority: Priority.high,
  );
  const NotificationDetails notifyDetails =
      NotificationDetails(android: androidDetails);

  await flutterLocalNotificationsPlugin.schedule(
    0, // 唯一通知ID
    '集市日提醒',
    '今天是小镇集市日，别错过啦！',
    notifyTime,
    notifyDetails,
    androidAllowWhileIdle: true, // 后台也能触发通知
  );
}

4. 处理通知开关状态
   用SharedPreferences保存用户的通知开关状态，切换时同步开启/取消通知：

// 保存通知开关状态
void saveNotificationEnabled(bool enabled) async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  await prefs.setBool('notification_enabled', enabled);
}

// 获取通知开关状态
Future<bool> getNotificationEnabled() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  return prefs.getBool('notification_enabled') ?? false;
}

// 切换通知逻辑
void toggleNotification(bool value, DateTime nextMarketDay) async {
  await saveNotificationEnabled(value);
  if (value) {
    bool granted = await requestNotificationPermission();
    if (granted) await scheduleMarketNotification(nextMarketDay);
  } else {
    await flutterLocalNotificationsPlugin.cancel(0); // 取消已设置的通知
  }
}

三、UI与逻辑结合 #

页面初始化时加载数据并更新UI：

@override
void initState() {
  super.initState();
  _initPageData();
}

Future<void> _initPageData() async {
  DateTime? baseDay = await getBaseMarketDay();
  if (baseDay == null) {
    // 无基准日时引导用户选择，或默认当前日期
    baseDay = DateTime.now();
    await saveBaseMarketDay(baseDay);
  }
  DateTime nextMarket = calculateNextMarketDay(baseDay, DateTime.now());
  bool notifyEnabled = await getNotificationEnabled();
  
  setState(() {
    _nextMarketDay = nextMarket;
    _notificationEnabled = notifyEnabled;
  });
}

最后在checkbox的onChanged回调中调用toggleNotification方法即可。

内容的提问来源于stack exchange，提问作者thebigbrownBox