我尝试在flutter应用程序中通过fcm显示后台通知。然而，我不知道为什么我创建的通知没有显示，但有另一个与消防商店数据库显示相同的值。我是这样创建通知的：

@pragma('vm:entry-point')
  Future<void> registerBackgroundMessage(RemoteMessage message) async {
    await Firebase.initializeApp();

    AppLogger.log("background", message.data);
    RemoteNotification? notification = message.notification;
    AndroidNotification? android = message.notification?.android;

    AppLogger.log(" --- bACKGROUND message received ---", "");
    AppLogger.log("Title", message.notification!.title);
    AppLogger.log("Body", message.notification!.body);
    final String payload = message.data['version'];

    String smallIcon = 'drawable/small_launcher_icon';
    if (notification != null && android != null) {
      flutterLocalNotificationsPlugin.show(
          notification.hashCode,
          notification.title,
          notification.body,
          NotificationDetails(
            android: AndroidNotificationDetails(
              'channel_id',
              'channel_name',
              importance: Importance.max,
              priority: Priority.high,
              ticker: 'New message received',
              icon: smallIcon,
              playSound: true,
              enableVibration: true,
              largeIcon:
                  const DrawableResourceAndroidBitmap('mipmap/launcher_icon'),
              color: const Color.fromARGB(255, 0, 123, 255),
              ledColor: const Color.fromARGB(255, 255, 0, 0),
              ledOnMs: 1000,
              ongoing: true,
              ledOffMs: 500,
            ),
          ));
    }
    return Future.value();
  }

这就是我在main（）中调用它的方式：

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await EasyLocalization.ensureInitialized();
  await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);
  MessagingService _msgService = MessagingService();

  await _msgService.init();
  FirebaseMessaging.onBackgroundMessage(_msgService.registerBackgroundMessage);

这是messagingService中的init方法：

Future<void> init() async {
    await _requestPermission();
    _deviceId = await getDeviceId();

    AppLogger.log("DeviceId", _deviceId);

    _firebaseMessaging.getToken().then((token) async {
      AppLogger.log("FCM TOKEN", token);

      saveTokens(token!);
    });
    await flutterLocalNotificationsPlugin
        .resolvePlatformSpecificImplementation<
            AndroidFlutterLocalNotificationsPlugin>()
        ?.createNotificationChannel(channel);
    FirebaseMessaging.instance.getInitialMessage().then((message) {
      print("FirebaseMessaging.getInitialMessage");
});

Ps：当我收到通知时，我在cosole中得到了这些错误：W/FLTFireMsgService（30433）：无法在Dart中处理后台消息，因为尚未注册onBackgroundMessage处理程序。W/FirebaseMessaging（30433）：应用尚未创建AndroidManifest.xml中设置的通知通道。将使用默认值。这是AndroidManifest.xml：

<meta-data
    android:name="com.google.firebase.messaging.default_notification_channel_id"

             android:value="@string/default_notification_channel_id" />

这是strings.xml：

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="default_notification_channel_id" translatable="false">fcm_default_channel</string>
</resources>

提前感谢您提出一些解决方案来解决我的问题。