Flutter:FCM 未处理异常:对空值使用空检查运算符 [英] Flutter: FCM Unhandled Exception: Null check operator used on a null value

问题描述

E/flutter (26872): [错误:flutter/lib/ui/ui_dart_state.cc(199)]未处理的异常:对空值使用空检查运算符E/颤振(26872):#0
MethodChannelFirebaseMessaging.registerBackgroundMessageHandler(包:firebase_messaging_platform_interface/src/method_channel/method_channel_messaging.dart:173:53)E/颤振(26872):#1
FirebaseMessagingPlatform.onBackgroundMessage=(包:firebase_messaging_platform_interface/src/platform_interface/platform_interface_messaging.dart:108:16)

E/flutter (26872): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Null check operator used on a null value E/flutter (26872): #0
MethodChannelFirebaseMessaging.registerBackgroundMessageHandler (package:firebase_messaging_platform_interface/src/method_channel/method_channel_messaging.dart:173:53) E/flutter (26872): #1
FirebaseMessagingPlatform.onBackgroundMessage= (package:firebase_messaging_platform_interface/src/platform_interface/platform_interface_messaging.dart:108:16)

// Background Messaging Set Up
    Future<void> _firebaseMessagingBackgroundHandler(
        RemoteMessage message) async {
      print('background message');
    }

    FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
    runApp(....)

我在 Android 系统上收到此代码的错误.一切正常，除非应用程序终止.

I am getting an error for this code on Android system. Everything works except when the app is terminated.

什么适用于 Android:

• 终止时的通知，onBackground 和 onForeground
• 仅在前台显示日期

什么在 Android 上不起作用:

• 仅在 Terminated 和 onBackground 时数据

适用于 iOS 的内容:

• 终止时的通知，onBackground 和 onForeground
• 仅在前台显示日期

什么在 iOS 上不起作用:

• 仅在终止时提供数据，

我不知道为什么在 Android 系统上出现空值错误，我该如何解决这个问题?另外，当应用程序终止时，我无法在 iOS 上收到 Data only 推送通知是真的吗?

I have no clue why I am getting that null value error on Android system and how can I fix this issue? Also, is it true that I can not receive the Data only push notification on iOS when the app is terminated?

推荐答案

我和你一样有同样的错误，在同一行.我查看了 docs，它说明了关于后台消息处理程序的两件事.

I had the same error as like you, on the same line. I checked out docs and it says 2 things about background message handler.

1. 它不能是匿名函数.
2. 它必须是顶级函数(例如，不是需要初始化的类方法).

就我而言，它不是顶级函数，它是在类中声明的.当您将处理程序移出任何类或函数时，使其成为顶级函数并且不需要任何类或方法初始化，那么错误就会消失.

In my case it was not a top-level function, it was declared inside a class. When you move your handler out of any class or function, so that it is a top-level function and doesn't require any class or method initialisation then the error will be gone.

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