我在Flutter应用上使用SignalR推送通知，运行正常。我从后端收到消息，并使用flutter_local_notifications显示通知。问题是SignalR服务会在一段时间后关闭。我如何让我的应用在后台运行？甚至在重启时启动？
下面是我的代码：

import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:isolate_test/Model/UserMessageModel.dart';
import 'package:signalr_core/signalr_core.dart';
import 'EndPointService.dart';
import 'NotificationService.dart';

class SignalRProvider {
  static String appName = "NOTIFICATION";
  static String? userName = "";
  static String deviceName = "android_app";
  static List<UserMessageModel> messages = <UserMessageModel>[];

  HubConnection connection = HubConnectionBuilder()
      .withUrl(
          'my_url',
          HttpConnectionOptions(
            logging: (level, message) => print(message),
          ))
      .withAutomaticReconnect()
      .withHubProtocol(JsonHubProtocol())
      .build();
  Function(bool update)? onMessagesUpdateCallback;
  SignalRProvider({
    this.onMessagesUpdateCallback,
  });

  setUsername(String username) {
    userName = username;
  }

  Future initSignalR(BuildContext context) async {
    WidgetsFlutterBinding.ensureInitialized();
    await NotificationService().init();
    connection.on('SignalRUserReceiveMessage', (message) async {
      var data = message!.first;
      if (data != null) {
        UserMessageModel msg = UserMessageModel.fromJson(data);
        messages.add(msg);
        msg.showNotification();
      }
      if (onMessagesUpdateCallback != null) {
        onMessagesUpdateCallback!(true);
      }
    });

    connection.on('SignalRMonitoringMessage', (message) async {
      var data = message!.first;
      if (data != null) {
        UserMessageModel msg = UserMessageModel.fromJson(data);
        messages.add(msg);
        msg.showNotification();
      }
      if (onMessagesUpdateCallback != null) {
        onMessagesUpdateCallback!(true);
      }
    });

    connection.on("SignalRReceiveConnectedMessage", (message) async {
      await connection.send(methodName: 'SignalRInit', args: [
        userName,
        appName,
        connection.connectionId,
      ]);
    });
    connection.on("SignalRReceiveDisconnectedMessage", (message) async {
      if (connection.state == HubConnectionState.disconnected) {
        connection.start();
      }
    });
    await connection.start();
  }

  List<UserMessageModel> getMessages() {
    return messages;
  }

  Future deleteMessage(UserMessageModel _msg) async {
    if (_msg == null) return;
    var response =
        await EndPointService().SetupApi("Message", "", []).httpDelete(
      HeaderEnum.BasicHeaderEnum,
      ResponseEnum.ResponseModelEnum,
      jsonEncode(_msg),
    );
  }

  addOrUpdateMessage(UserMessageModel _msg) {
    if (_msg == null) return;
    if (messages != null) {
      var found =
          messages.firstWhere((e) => e.user == _msg.user && e.id == _msg.id);
      var index =
          messages.indexWhere((e) => e.user == _msg.user && e.id == _msg.id);
      if (found != null) {
        messages[index] = _msg;
      } else {
        messages.add(_msg);
      }
      if (onMessagesUpdateCallback != null) {
        onMessagesUpdateCallback!(true);
      }
    }
  }

  setMessagesUpdateCallback(Function(bool update) func) {
    onMessagesUpdateCallback = func;
  }
}