firebase - Flutter FCM onBackgroundMessage 不适用于嵌套的非静态方法调用

Question

我正在使用 firebase_messaging 6.0.9与 flutter 1.12.13 .在 repo 的自述文件中:https://pub.dev/packages/firebase_messaging#-readme-tab-它说要声明 onBackgroudMessage回调作为静态或顶级方法。我做了，但是当这个回调调用非静态方法时它不起作用。以下示例使用单例类演示了这一点:

class NotificationService {

  static NotificationService _instance;

  final FirebaseMessaging _firebase;

  static NotificationService get instance => _instance;

  NotificationService._internal() : this._firebase = FirebaseMessaging();

  factory NotificationService() {
    if (_instance == null) {
      _instance = NotificationService._internal();
      _instance._firebase.configure(
          onBackgroundMessage: NotificationService.staticHandler
      );
    }

    return _instance;
  }

  static Future<dynamic> staticHandler(Map<String, dynamic> msg) {
    print("Static Func >>> $msg"); // Successfully prints
    return NotificationService.instance.instanceFunc(msg); // Fails here, complaining that it's being invoked on null.
  }

  Future<dynamic> instanceFunc(Map<String, dynamic> msg) {
    print("Instance Func >>> $msg");
  }

  void myVarFunc() {
    print("This is my var func");
  }
}

在 main.dart ，调用通知服务工厂构造函数:

import 'package:myProject/services/notification/notification_service.dart';

run(MyApp());

class MyApp extends StatelessWidget {
   final NotificationService _ns = NotificationService();
   NotificationService.instance.myVarFunc(); // Prints successfully.
   .......
   .......
   .......
}

instanceFunc 的调用失败，说它是在 null 上调用的。以下是日志:

I/flutter ( 6935): Static Func >>> {data: {title: Title_is_here, message: Message_is_here}}
I/flutter ( 6935): Unable to handle incoming background message.
I/flutter ( 6935): NoSuchMethodError: The method 'instanceFunc' was called on null.
I/flutter ( 6935): Receiver: null
I/flutter ( 6935): Tried calling: instanceFunc(_LinkedHashMap len:1)

我不确定这是否是处理这种情况的正确方法。由于我是 Dart 和 Flutter 的新手，我的知识非常有限。我不能声明一切都是静态的并且可以工作，这不是 IMO 的好设计。我可能在这里遗漏了一些东西。

Answer 1

有一些原因没有在 onBackgroundMessage 上获得回调:-

onBackgroundMessage 在 iOS 上不起作用，所以你必须实现平台检查

例如:-

    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> message) async {
        printDebug("onMessage foreground: $message");
      },
      onBackgroundMessage: Platform.isIOS ? null : _myBackgroundMessageHandler,
      onLaunch: (Map<String, dynamic> message) async {
        printDebug("onLaunch Kill: $message");
      },
      onResume: (Map<String, dynamic> message) async {
        print("onResume Background: $message");
      },
    );
    static Future<dynamic> _myBackgroundMessageHandler(
      Map<String, dynamic> message) async {
    print("onBackgroundMessage: $message");
    return Future<void>.value();
   }

并且您必须确保您的通知有效负载不包含通知 key ，因为如果有效负载中存在通知 key ，那么通知将由您的系统直接处理。因此，您必须从有效负载中删除通知键才能在 onBackgroundMessage 上获得回调。

注意:- 如果您删除通知键，则通知不会在系统通知托盘中呈现。为此，您可以在本地通知。