我已经使用flutter_local_notification包创建了一个自定义通知，当我使用FCM发送通知时，两个通知在应用程序的前台和后台状态都可见。当我点击FCM生成的通知时，其工作正常，但当点击自定义后台通知时，我的应用程序启动，但无法运行我的逻辑，所以请帮助我处理后台自定义通知
点击后台自定义通知时，会显示以下信息
尝试启动重复的背景分离菌株。正在返回...

class NotificationService {
  static final NotificationService _notificationService =
      NotificationService._private();
  NotificationService._private();
  factory NotificationService() => _notificationService;

  final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
      FlutterLocalNotificationsPlugin();

  final AndroidNotificationChannel _androidChannel =
      const AndroidNotificationChannel(
          'high_importance_channel', // id
          'Notifications', // title
          description: 'important notification channel', // description
          importance: Importance.high,
          playSound: true);

  final AndroidInitializationSettings _initializationSettingsAndroid =
      const AndroidInitializationSettings(
    'app_icon',
  );

  ///This functions initializes Flutterlocalnotificationplugin with required settings and channels
  initialize() async {
    AndroidFlutterLocalNotificationsPlugin? resp =
        flutterLocalNotificationsPlugin.resolvePlatformSpecificImplementation<
            AndroidFlutterLocalNotificationsPlugin>();

    await resp!.createNotificationChannel(_androidChannel);
    resp.requestPermission();

    var initializationSettings =
        InitializationSettings(android: _initializationSettingsAndroid);

    await flutterLocalNotificationsPlugin.initialize(initializationSettings,
        onDidReceiveNotificationResponse: _handleForegroundNotification,
        onDidReceiveBackgroundNotificationResponse:
            _handleBackgroundNotification);
  }

  /// This function create the custom notifcation.
  /// before calling this function , firebaseLocalNotification instance should be initialized
  showNotification(RemoteMessage message) {
    var initializationSettings =
        InitializationSettings(android: _initializationSettingsAndroid);

    flutterLocalNotificationsPlugin.initialize(initializationSettings,
        onDidReceiveNotificationResponse: _handleForegroundNotification,
        onDidReceiveBackgroundNotificationResponse:
            _handleBackgroundNotification);
    flutterLocalNotificationsPlugin.show(
        1123,
        message.data['title'],
        message.data['body'],
        const NotificationDetails(
          android: AndroidNotificationDetails(
            '1123',
            'channel.name',
            channelDescription: 'channel.description',
            color: Colors.blue,
            playSound: true,
          ),
        ));
  }
}

///This functions handle background notification press and performs given instructions
@pragma('vm:entry-point')
_handleBackgroundNotification(NotificationResponse response) async {
  await Future.delayed(Duration(seconds: 3));
  Fluttertoast.showToast(
      msg: "backgrrrround call nice no",
      toastLength: Toast.LENGTH_SHORT,
      gravity: ToastGravity.CENTER,
      timeInSecForIosWeb: 1,
      backgroundColor: Colors.red,
      textColor: Colors.white,
      fontSize: 16.0);
}

///This functions handel foregroud notification press and performs given instruction
_handleForegroundNotification(NotificationResponse response) async {
  await Future.delayed(Duration(seconds: 3));
  Fluttertoast.showToast(
      msg: "Forerground call nice no",
      toastLength: Toast.LENGTH_SHORT,
      gravity: ToastGravity.CENTER,
      timeInSecForIosWeb: 1,
      backgroundColor: Colors.red,
      textColor: Colors.white,
      fontSize: 16.0);
}

另一类用于管理FCM

class FCMService {
  final FirebaseMessaging _firebaseMessaging = FirebaseMessaging.instance;
  String? fcmToken;

  ///This function initialized FCM and start stream of token,foregroundmessage,backgroundmessage
  initialize() async {
    fcmToken = await FirebaseMessaging.instance.getToken();
    await FirebaseMessaging.instance
        .setForegroundNotificationPresentationOptions(
      alert: true,
      badge: true,
      sound: true,
    );
    debugPrint(fcmToken);
    _listenToTokenStream();
    _listenToForegroundMessage();
  }

  // /Handle  background but not teminated app notification press
  _listenToOnMessageOpenedApp() {
    //when
    FirebaseMessaging.onMessageOpenedApp.listen((message) {
      print("FCM>>>>>>>> backgroud");
    });
  }

  /// Request permission for higher sdk version
  _requestNotificationPermission() async {
    NotificationSettings settings = await _firebaseMessaging.requestPermission(
      alert: true,
      sound: true,
    );
    debugPrint('User granted permission: ${settings.authorizationStatus}');
  }

  /// listen to foreground message recieved from FCM
  _listenToForegroundMessage() {
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      NotificationService().showNotification(message);
    });
  }

  ///Listen to streamm of token when token expires helps us to updat it
  _listenToTokenStream() {
    FirebaseMessaging.instance.onTokenRefresh.listen((token) {
      fcmToken = token;
      debugPrint(fcmToken);
    }).onError((e) {
      debugPrint("token refresh failed");
    });
  }
}

///listen background message recieve from FCM , DO NOT: perform heavy task in background
///otherwise your process may get killed

Future<void> fcmBackgroundMessageHandler(RemoteMessage message) async {
  await Firebase.initializeApp();
  // await NotificationService().initialize();
  NotificationService().showNotification(message);
}

主要方法：

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  FCMService().initialize();
  NotificationService().initialize();
  FirebaseMessaging.onBackgroundMessage(fcmBackgroundMessageHandler);
  runApp(const MyApp());
}