我正在开发一个应用程序的推送通知使用FCM，当应用程序在后台或终止，并收到新的通知，我需要保存此通知本地的数据（SQLITE），没有点击通知或重新打开应用程序再次，通知不会在应用程序中读取，除非点击。
这是我的通知处理程序. dart

import 'dart:async';
import 'dart:io';
import 'package:eshaar/model/message.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:intl/intl.dart';
import 'package:eshaar/model/database_helper.dart';

FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
new FlutterLocalNotificationsPlugin();

Future<dynamic> myBackgroundMessageHandler(Map<String, dynamic> message) async {
  print("onBackgroundMessage: $message");
  //_showBigPictureNotification(message);
  return Future<void>.value();
}

Future onSelectNotification(String payload) async {

}

class NotificationHandler {
  FirebaseMessaging _fcm = FirebaseMessaging();
  StreamSubscription iosSubscription;
  DatabaseHelper db = new DatabaseHelper();
  static final NotificationHandler _singleton =
  new NotificationHandler._internal();

  factory NotificationHandler() {
    return _singleton;
  }
  NotificationHandler._internal();

  initializeFcmNotification() async {
    var initializationSettingsAndroid =
    new AndroidInitializationSettings('mipmap/ic_launcher');
    var initializationSettingsIOS = new IOSInitializationSettings(
        onDidReceiveLocalNotification: onDidReceiveLocalNotification);
    var initializationSettings = new InitializationSettings(
        initializationSettingsAndroid, initializationSettingsIOS);
    flutterLocalNotificationsPlugin.initialize(initializationSettings,
        onSelectNotification: onSelectNotification);

    if (Platform.isIOS) {
      iosSubscription = _fcm.onIosSettingsRegistered.listen((data) {
        // save the token  OR subscribe to a topic here
      });

      _fcm.requestNotificationPermissions(IosNotificationSettings());
    } else {
      _saveDeviceToken();
    }

    _fcm.configure(
      onMessage: (Map<String, dynamic> message) async {
        print("---------------------On Message--------------------");
        displayNotification(message['data']['title'],message['data']['body']);
        _saveNotificationToLocal(message);
      },
      onBackgroundMessage: Platform.isIOS ? null : myBackgroundMessageHandler ,
      onLaunch: (Map<String, dynamic> message) async {
        print("---------------------On Lunch--------------------");
        _saveNotificationToLocal(message);
      },
      onResume: (Map<String, dynamic> message) async {
        print("---------------------On Resume--------------------");
        _saveNotificationToLocal(message);
      },
    );
  }

  _saveNotificationToLocal(Map<String, dynamic> message){
    String sender_id = message['data']['sender_id'];
    String message_id = message['data']['message_id'];
    String title = message['data']['title'];
    String body = message['data']['body'];
    String del_time  = getCurrentDateTime();
    Messages msg = new Messages(sender_id,message_id,title,body,del_time);
    db.saveMessages(msg);

  }

 String getCurrentDateTime(){
   var now = new DateTime.now();
   var formatter = new DateFormat('MMM d yy h:mm a');
   String formatted = formatter.format(now);
   return formatted;
  }

  /// Get the token, save it to the database for current user
  _saveDeviceToken() async {
    String fcmToken = await _fcm.getToken();
  }

  Future<void> onDidReceiveLocalNotification(
      int id, String title, String body, String payload) async {
    // display a dialog with the notification details, tap ok to go to another page
  }

  void displayNotification(String title,String body) async{
    var androidPlatformChannelSpecifics = AndroidNotificationDetails(
        'your channel id', 'your channel name', 'your channel description',
        importance: Importance.Max, priority: Priority.High, ticker: 'ticker');
    var iOSPlatformChannelSpecifics = IOSNotificationDetails();
    var platformChannelSpecifics = NotificationDetails(
        androidPlatformChannelSpecifics, iOSPlatformChannelSpecifics);
    await flutterLocalNotificationsPlugin.show(
        0, '$title', '$body', platformChannelSpecifics,
        payload: 'item x');
  }
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="ot.eshaar.eshaar">
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
    <uses-permission android:name="android.permission.VIBRATE" />


    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
         calls FlutterMain.startInitialization(this); in its onCreate method.
         In most cases you can leave this as-is, but you if you want to provide
         additional functionality it is fine to subclass or reimplement
         FlutterApplication and put your custom class here. -->
    <application
        android:name=".Application"
        android:label="eshaar"
        android:icon="@mipmap/ic_launcher">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">
            <!-- This keeps the window background of the activity showing
                 until Flutter renders its first frame. It can be removed if
                 there is no splash screen (such as the default splash screen
                 defined in @style/LaunchTheme). -->
            <meta-data
                android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
                android:value="true" />

            <meta-data
                    android:name="com.google.firebase.messaging.android.channel_id"
                    android:value="mmne" />

            <meta-data android:name="com.google.firebase.messaging.default_notification_channel_id" android:value="@string/default_notification_channel_id"/>

            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>

            <intent-filter>
                <action android:name="FLUTTER_NOTIFICATION_CLICK" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <receiver android:name="com.dexterous.flutterlocalnotifications.ScheduledNotificationBootReceiver">
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED"></action>
            </intent-filter>
        </receiver>
        <receiver android:name="com.dexterous.flutterlocalnotifications.ScheduledNotificationReceiver" />

    </application>
</manifest>

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