在Flutter中，可以使用flutter_local_notifications插件来实现AndroidAlarmManager无效日期的问题。以下是一个示例代码：

1. 首先，添加flutter_local_notifications插件到pubspec.yaml文件中：

dependencies:
  flutter:
    sdk: flutter
  flutter_local_notifications: ^6.0.0

2. 在Dart文件中，导入flutter_local_notifications和dart:io库：

import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';

3. 创建一个FlutterLocalNotificationsPlugin实例，并在初始化方法中配置通知设置：

FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
    FlutterLocalNotificationsPlugin();

Future initNotifications() async {
  var initializationSettingsAndroid =
      AndroidInitializationSettings('@mipmap/ic_launcher');
  var initializationSettingsIOS = IOSInitializationSettings();
  var initializationSettings = InitializationSettings(
      android: initializationSettingsAndroid, iOS: initializationSettingsIOS);
  await flutterLocalNotificationsPlugin.initialize(initializationSettings);
}

4. 在主函数中调用initNotifications方法来初始化通知设置：

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await initNotifications();
  runApp(MyApp());
}

5. 创建一个函数来设置定时通知。在该函数中，你可以使用flutter_local_notifications插件的方法来设置通知的标题、内容和触发时间：

Future scheduleNotification(int id, String title, String body,
    DateTime scheduledDateTime) async {
  var androidPlatformChannelSpecifics = AndroidNotificationDetails(
    'your channel id',
    'your channel name',
    'your channel description',
  );
  var iOSPlatformChannelSpecifics = IOSNotificationDetails();
  var platformChannelSpecifics = NotificationDetails(
      android: androidPlatformChannelSpecifics,
      iOS: iOSPlatformChannelSpecifics);
  await flutterLocalNotificationsPlugin.schedule(
      id, title, body, scheduledDateTime, platformChannelSpecifics);
}

6. 在需要调度通知的地方调用scheduleNotification函数，并传入通知的id、标题、内容和触发时间。例如，在一个按钮的回调函数中调用该函数：

RaisedButton(
  onPressed: () {
    scheduleNotification(
        0,
        'Notification title',
        'Notification body',
        DateTime.now().add(Duration(seconds: 5)));
  },
  child: Text('Schedule Notification'),
)

这样，当用户点击按钮时，将会在5秒后收到一个定时通知。

通过以上步骤，您可以在Flutter中使用flutter_local_notifications插件来解决AndroidAlarmManager无效日期的问题。