Flutter平台特定通知功能：实现iOS与Android的通知系统

一、Flutter通知概述

Flutter作为一款跨平台的移动应用开发框架，在通知功能的实现上为开发者提供了强大且灵活的解决方案。通知对于移动应用而言至关重要，它能在应用处于后台甚至关闭状态时，有效地向用户传达重要信息，提升用户的参与度和留存率。

Flutter本身提供了一些通用的通知插件，如flutter_local_notifications，它允许开发者创建本地通知，而无需过多关注底层平台的差异。然而，在实际开发中，针对iOS和Android平台的特性，开发者可能需要实现一些特定的通知功能，以提供更原生、更符合用户习惯的体验。

二、iOS通知系统的集成与定制

（一）iOS通知权限

在iOS上，应用需要请求用户授权才能发送通知。Flutter中，可以使用flutter_local_notifications插件来实现权限请求。首先，在pubspec.yaml文件中添加依赖：

dependencies:
  flutter_local_notifications: ^8.0.0+4

然后，在代码中初始化并请求权限：

import 'package:flutter_local_notifications/flutter_local_notifications.dart';

final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();

Future<void> requestIOSPermissions() async {
  final IOSFlutterLocalNotificationsSettings initializationSettingsIOS =
      IOSFlutterLocalNotificationsSettings(
    requestAlertPermission: true,
    requestBadgePermission: true,
    requestSoundPermission: true,
  );

  final InitializationSettings initializationSettings = InitializationSettings(
    iOS: initializationSettingsIOS,
  );
  await flutterLocalNotificationsPlugin.initialize(initializationSettings);

  final bool? granted = await flutterLocalNotificationsPlugin
     .resolvePlatformSpecificImplementation<
          IOSFlutterLocalNotificationsPlugin>()
     ?.requestPermissions(
        alert: true,
        badge: true,
        sound: true,
      );
  print('Notification permissions granted: $granted');
}

这段代码首先配置了iOS通知的初始化设置，包括请求提醒、徽章和声音权限。然后初始化flutter_local_notifications插件，并请求通知权限。

（二）iOS通知样式定制

基本通知样式 iOS上的基本通知样式相对简洁，开发者可以设置标题、正文、附件等。使用flutter_local_notifications插件发送基本通知：

Future<void> showIOSBasicNotification() async {
  const AndroidNotificationDetails androidPlatformChannelSpecifics =
      AndroidNotificationDetails(
    'your channel id',
    'your channel name',
    channelDescription: 'your channel description',
    importance: Importance.max,
    priority: Priority.high,
  );
  const IOSNotificationDetails iOSPlatformChannelSpecifics =
      IOSNotificationDetails();
  const NotificationDetails platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics,
    iOS: iOSPlatformChannelSpecifics,
  );
  await flutterLocalNotificationsPlugin.show(
    0,
    'iOS Basic Notification',
    'This is a basic iOS notification',
    platformChannelSpecifics,
  );
}

这里创建了AndroidNotificationDetails和IOSNotificationDetails，并将它们组合成NotificationDetails，然后使用show方法发送通知。

富文本通知样式 iOS支持富文本通知，允许在通知中展示图片、视频等附件。要实现富文本通知，需要先将附件下载到本地，然后在通知中引用。

import 'dart:io';
import 'package:http/http.dart' as http;
import 'package:path_provider/path_provider.dart';

Future<void> showIOSRichNotification() async {
  final String imageUrl = 'https://example.com/image.jpg';
  final Directory appDocDir = await getApplicationDocumentsDirectory();
  final String filePath = '${appDocDir.path}/image.jpg';
  final http.Response response = await http.get(Uri.parse(imageUrl));
  final File file = File(filePath);
  await file.writeAsBytes(response.bodyBytes);

  final IOSNotificationAttachment attachment =
      await IOSNotificationAttachment.fromPath(filePath);

  const AndroidNotificationDetails androidPlatformChannelSpecifics =
      AndroidNotificationDetails(
    'your channel id',
    'your channel name',
    channelDescription: 'your channel description',
    importance: Importance.max,
    priority: Priority.high,
  );
  const IOSNotificationDetails iOSPlatformChannelSpecifics =
      IOSNotificationDetails(attachments: [attachment]);
  const NotificationDetails platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics,
    iOS: iOSPlatformChannelSpecifics,
  );
  await flutterLocalNotificationsPlugin.show(
    1,
    'iOS Rich Notification',
    'This is a rich iOS notification with an image',
    platformChannelSpecifics,
  );
}

这段代码从网络下载一张图片，保存到本地，然后创建IOSNotificationAttachment并将其添加到通知中，从而实现富文本通知。

（三）处理iOS通知交互

iOS通知支持用户与通知进行交互，如点击按钮、回复等。以点击通知跳转到应用内特定页面为例：

注册通知处理回调 在main.dart中初始化时注册回调：

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
      FlutterLocalNotificationsPlugin();

  final IOSFlutterLocalNotificationsSettings initializationSettingsIOS =
      IOSFlutterLocalNotificationsSettings(
    requestAlertPermission: true,
    requestBadgePermission: true,
    requestSoundPermission: true,
  );

  final InitializationSettings initializationSettings = InitializationSettings(
    iOS: initializationSettingsIOS,
  );
  await flutterLocalNotificationsPlugin.initialize(initializationSettings,
      onSelectNotification: (String? payload) async {
    if (payload != null) {
      print('Notification payload: $payload');
      // 跳转到特定页面
      Navigator.push(
        context,
        MaterialPageRoute(builder: (context) => SpecificPage(payload: payload)),
      );
    }
  });

  runApp(MyApp());
}

发送带有payload的通知

Future<void> sendIOSNotificationWithPayload() async {
  const AndroidNotificationDetails androidPlatformChannelSpecifics =
      AndroidNotificationDetails(
    'your channel id',
    'your channel name',
    channelDescription: 'your channel description',
    importance: Importance.max,
    priority: Priority.high,
  );
  const IOSNotificationDetails iOSPlatformChannelSpecifics =
      IOSNotificationDetails();
  const NotificationDetails platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics,
    iOS: iOSPlatformChannelSpecifics,
  );
  await flutterLocalNotificationsPlugin.show(
    2,
    'iOS Notification with Payload',
    'This is a notification with a payload',
    platformChannelSpecifics,
    payload: 'page_1',
  );
}

这里在发送通知时添加了payload，当用户点击通知时，会触发onSelectNotification回调，根据payload跳转到相应的页面。

三、Android通知系统的集成与定制

（一）Android通知渠道

Android从Oreo（API 26）开始引入通知渠道的概念。每个通知都必须分配到一个渠道，不同渠道可以设置不同的通知行为，如声音、震动等。

创建通知渠道

import 'package:flutter_local_notifications/flutter_local_notifications.dart';

Future<void> createAndroidNotificationChannel() async {
  final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
      FlutterLocalNotificationsPlugin();

  const AndroidNotificationChannel channel = AndroidNotificationChannel(
    'high_importance_channel',
    'High Importance Notifications',
    description: 'This channel is used for important notifications.',
    importance: Importance.high,
  );

  await flutterLocalNotificationsPlugin
     .resolvePlatformSpecificImplementation<
          AndroidFlutterLocalNotificationsPlugin>()
     ?.createNotificationChannel(channel);
}

使用通知渠道发送通知

Future<void> showAndroidNotification() async {
  await createAndroidNotificationChannel();

  const AndroidNotificationDetails androidPlatformChannelSpecifics =
      AndroidNotificationDetails(
    'high_importance_channel',
    'High Importance Notifications',
    channelDescription: 'This channel is used for important notifications.',
    importance: Importance.high,
    priority: Priority.high,
  );
  const NotificationDetails platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics,
  );
  await flutterLocalNotificationsPlugin.show(
    3,
    'Android Notification',
    'This is an Android notification',
    platformChannelSpecifics,
  );
}

这段代码首先创建了一个高重要性的通知渠道，然后使用该渠道发送通知。

（二）Android通知样式定制

基本通知样式 Android的基本通知样式与iOS有所不同，开发者可以设置标题、正文、小图标等。

Future<void> showAndroidBasicNotification() async {
  const AndroidNotificationDetails androidPlatformChannelSpecifics =
      AndroidNotificationDetails(
    'your channel id',
    'your channel name',
    channelDescription: 'your channel description',
    importance: Importance.max,
    priority: Priority.high,
    icon: '@mipmap/ic_launcher',
    largeIcon: DrawableResourceAndroidBitmap('@mipmap/ic_launcher'),
  );
  const NotificationDetails platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics,
  );
  await flutterLocalNotificationsPlugin.show(
    4,
    'Android Basic Notification',
    'This is a basic Android notification',
    platformChannelSpecifics,
  );
}

这里设置了通知的小图标icon和大图标largeIcon，使通知更具辨识度。

扩展通知样式 Android支持扩展通知样式，如大文本样式、大图片样式等。以大图片样式为例：

import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:http/http.dart' as http;
import 'package:path_provider/path_provider.dart';
import 'dart:io';

Future<void> showAndroidBigPictureNotification() async {
  final String imageUrl = 'https://example.com/big_image.jpg';
  final Directory appDocDir = await getApplicationDocumentsDirectory();
  final String filePath = '${appDocDir.path}/big_image.jpg';
  final http.Response response = await http.get(Uri.parse(imageUrl));
  final File file = File(filePath);
  await file.writeAsBytes(response.bodyBytes);

  final AndroidNotificationDetails androidPlatformChannelSpecifics =
      AndroidNotificationDetails(
    'your channel id',
    'your channel name',
    channelDescription: 'your channel description',
    importance: Importance.max,
    priority: Priority.high,
    styleInformation: BigPictureStyleInformation(
      FilePathAndroidBitmap(filePath),
      hideExpandedLargeIcon: true,
      contentTitle: 'Big Picture Notification',
      summaryText: 'This is a big picture notification on Android',
    ),
  );
  const NotificationDetails platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics,
  );
  await flutterLocalNotificationsPlugin.show(
    5,
    'Android Big Picture Notification',
    'This is a big picture Android notification',
    platformChannelSpecifics,
  );
}

这段代码下载一张图片，然后使用BigPictureStyleInformation将其设置为通知的大图片样式。

（三）处理Android通知交互

Android通知同样支持用户交互，如点击通知跳转到应用内特定页面，或者添加自定义按钮。以添加自定义按钮为例：

创建通知并添加按钮

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

Future<void> showAndroidNotificationWithAction() async {
  const AndroidNotificationDetails androidPlatformChannelSpecifics =
      AndroidNotificationDetails(
    'your channel id',
    'your channel name',
    channelDescription: 'your channel description',
    importance: Importance.max,
    priority: Priority.high,
    actions: [
      AndroidNotificationAction(
        'action_id_1',
        'Button 1',
        showsUserInterface: true,
      ),
      AndroidNotificationAction(
        'action_id_2',
        'Button 2',
        showsUserInterface: true,
      ),
    ],
  );
  const NotificationDetails platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics,
  );
  await flutterLocalNotificationsPlugin.show(
    6,
    'Android Notification with Action',
    'This is a notification with action buttons',
    platformChannelSpecifics,
  );
}

处理按钮点击事件 在main.dart中注册回调处理按钮点击：

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
      FlutterLocalNotificationsPlugin();

  const AndroidNotificationChannel channel = AndroidNotificationChannel(
    'high_importance_channel',
    'High Importance Notifications',
    description: 'This channel is used for important notifications.',
    importance: Importance.high,
  );

  await flutterLocalNotificationsPlugin
     .resolvePlatformSpecificImplementation<
          AndroidFlutterLocalNotificationsPlugin>()
     ?.createNotificationChannel(channel);

  const InitializationSettings initializationSettings = InitializationSettings(
    android: AndroidInitializationSettings('@mipmap/ic_launcher'),
  );
  await flutterLocalNotificationsPlugin.initialize(initializationSettings,
      onSelectNotification: (String? payload) async {
    if (payload != null) {
      print('Notification payload: $payload');
    }
  }, onDidReceiveNotificationResponse: (NotificationResponse details) {
    final String? payload = details.payload;
    if (details.notificationResponseType ==
        NotificationResponseType.action) {
      if (details.actionId == 'action_id_1') {
        print('Button 1 clicked');
      } else if (details.actionId == 'action_id_2') {
        print('Button 2 clicked');
      }
    }
  });

  runApp(MyApp());
}

这里在发送通知时添加了两个按钮，然后通过onDidReceiveNotificationResponse回调来处理按钮的点击事件。

四、跨平台通知的统一管理

虽然iOS和Android有各自独特的通知系统，但在Flutter开发中，可以通过封装来实现跨平台的统一管理。

创建通知服务类

import 'package:flutter_local_notifications/flutter_local_notifications.dart';

class NotificationService {
  static final NotificationService _instance = NotificationService._internal();
  factory NotificationService() => _instance;
  final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
      FlutterLocalNotificationsPlugin();

  NotificationService._internal();

  Future<void> initialize() async {
    const AndroidNotificationChannel channel = AndroidNotificationChannel(
      'high_importance_channel',
      'High Importance Notifications',
      description: 'This channel is used for important notifications.',
      importance: Importance.high,
    );

    await flutterLocalNotificationsPlugin
       .resolvePlatformSpecificImplementation<
            AndroidFlutterLocalNotificationsPlugin>()
       ?.createNotificationChannel(channel);

    final IOSFlutterLocalNotificationsSettings initializationSettingsIOS =
        IOSFlutterLocalNotificationsSettings(
      requestAlertPermission: true,
      requestBadgePermission: true,
      requestSoundPermission: true,
    );

    final InitializationSettings initializationSettings = InitializationSettings(
      android: AndroidInitializationSettings('@mipmap/ic_launcher'),
      iOS: initializationSettingsIOS,
    );
    await flutterLocalNotificationsPlugin.initialize(initializationSettings,
        onSelectNotification: (String? payload) async {
      if (payload != null) {
        print('Notification payload: $payload');
      }
    }, onDidReceiveNotificationResponse: (NotificationResponse details) {
      final String? payload = details.payload;
      if (details.notificationResponseType ==
          NotificationResponseType.action) {
        if (details.actionId == 'action_id_1') {
          print('Button 1 clicked');
        } else if (details.actionId == 'action_id_2') {
          print('Button 2 clicked');
        }
      }
    });
  }

  Future<void> showNotification(
      {required int id,
      required String title,
      required String body,
      String? payload}) async {
    const AndroidNotificationDetails androidPlatformChannelSpecifics =
        AndroidNotificationDetails(
      'high_importance_channel',
      'High Importance Notifications',
      channelDescription: 'This channel is used for important notifications.',
      importance: Importance.high,
      priority: Priority.high,
    );
    const IOSNotificationDetails iOSPlatformChannelSpecifics =
        IOSNotificationDetails();
    const NotificationDetails platformChannelSpecifics = NotificationDetails(
      android: androidPlatformChannelSpecifics,
      iOS: iOSPlatformChannelSpecifics,
    );
    await flutterLocalNotificationsPlugin.show(
      id,
      title,
      body,
      platformChannelSpecifics,
      payload: payload,
    );
  }
}

使用通知服务类 在需要发送通知的地方，使用NotificationService类：

import 'package:flutter/material.dart';
import 'package:your_project/notification_service.dart';

class HomePage extends StatelessWidget {
  final NotificationService notificationService = NotificationService();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Notification Example'),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: () async {
            await notificationService.initialize();
            await notificationService.showNotification(
              id: 7,
              title: 'Cross - Platform Notification',
              body: 'This is a cross - platform notification',
              payload: 'home_page',
            );
          },
          child: Text('Send Notification'),
        ),
      ),
    );
  }
}

通过这种方式，开发者可以在不同平台上统一管理通知的初始化、发送以及交互处理，提高代码的可维护性和复用性。

五、常见问题与解决方法

（一）通知不显示

原因
- 权限问题：在iOS上未请求到通知权限，或者在Android上未创建正确的通知渠道。
- 配置错误：通知的参数设置不正确，如在Android上未设置正确的图标，或者在iOS上未配置合适的通知样式。
解决方法
- iOS权限：仔细检查权限请求代码，确保用户授予了通知权限。可以在设备的设置中手动检查应用的通知权限。
- Android渠道：确认通知渠道的创建代码正确无误，并且在发送通知时使用了正确的渠道ID。
- 参数配置：检查通知的图标、标题、正文等参数是否设置正确。在Android上，图标资源路径要确保正确，如@mipmap/ic_launcher等。

（二）通知点击无响应

原因
- 回调未注册：在Flutter中，没有正确注册通知点击的回调函数，导致无法处理用户的点击操作。
- 上下文问题：在回调函数中使用了不正确的上下文，导致无法进行页面跳转等操作。
解决方法
- 注册回调：在flutter_local_notifications插件初始化时，正确注册onSelectNotification或onDidReceiveNotificationResponse回调函数。
- 上下文处理：在需要进行页面跳转等操作时，确保使用了正确的上下文。可以将全局的NavigatorKey传递到回调函数中，以便进行页面导航。

（三）iOS和Android通知样式不一致

原因
- 平台特性：iOS和Android本身的通知样式存在差异，即使使用相同的插件，也可能因为平台默认样式的不同而看起来不一致。
- 定制不足：开发者没有针对不同平台进行足够的样式定制，导致通知在不同平台上未能达到预期的效果。
解决方法
- 了解平台特性：深入了解iOS和Android通知样式的差异，根据不同平台的特点进行定制。例如，iOS的富文本通知和Android的大图片样式等，要分别按照平台的规范进行实现。
- 精细定制：对iOS和Android的通知样式进行精细定制，通过设置不同的参数，如iOS的attachments和Android的styleInformation等，使通知在不同平台上都能提供良好的用户体验。

通过对以上内容的深入学习和实践，开发者能够在Flutter应用中有效地实现iOS和Android平台特定的通知功能，为用户提供更加丰富、个性化的通知体验。同时，通过跨平台的统一管理和对常见问题的解决，能够提升应用的稳定性和用户满意度。