未处理的异常：在空值上使用空检查运算符 (Flutter FCM)

Question

我正在尝试为我的应用程序实现通知，但是在初始化通知时 FirebaseMessaging.onBackgroundMessage((message) => myBackgroundMessageHandler(message)) 出现以下错误。我查看了 and 并采用了我在 class 之外用作参数的函数 myBackgroundMessageHandler 但错误仍然存​​在。

错误如下：

E/flutter (10115): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Null check operator used on a null value E/flutter (10115): #0
MethodChannelFirebaseMessaging.registerBackgroundMessageHandler (package:firebase_messaging_platform_interface/src/method_channel/method_channel_messaging.dart:179:53) E/flutter (10115): #1
FirebaseMessagingPlatform.onBackgroundMessage= (package:firebase_messaging_platform_interface/src/platform_interface/platform_interface_messaging.dart:101:16) E/flutter (10115): #2 FirebaseMessaging.onBackgroundMessage (package:firebase_messaging/src/messaging.dart:83:31) E/flutter (10115): #3 main (package:okepos/main.dart:130:21) E/flutter (10115):

下面是我的代码：

Future<dynamic> myBackgroundMessageHandler(RemoteMessage message) {
  print('backgroundMessage: message => ${message.toString()}');

}


void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  FirebaseMessaging.onBackgroundMessage((message) => myBackgroundMessageHandler(message));

  }

Answer 1

您可能想尝试按以下方式编写您的主要功能。如果您想 运行 您的函数在后台运行，您可能需要初始化 Firebase。

Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  // If you're going to use other Firebase services in the background, such as Firestore,
  // make sure you call `initializeApp` before using other Firebase services.
  await Firebase.initializeApp();
  print('Handling a background message ${message.messageId}');
  if (message.notification != null) {
    print(message.notification.title);
    print(message.notification.body);
  }

  // Create a notification for this
}

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  // Background Message Handler
  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
  runApp(MyApp());
}

如果您想查看我使用 Flutter 实现的 Firebase 消息传递，请查看 my github repo。