如果处理后台消息，firebase_messaging flutter 插件会在启动时崩溃

Question

我将firebase_messaging v5.1.6与我的 flutter 应用程序集成，如自述文件中提到的“处理后台消息”选项。

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这是我的文件的外观。

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我的应用程序.kt

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class MyApplication : FlutterApplication(), PluginRegistrantCallback {\n    override fun onCreate() {\n        super.onCreate()\n        FlutterFirebaseMessagingService.setPluginRegistrant(this)\n    }\n\n    override fun registerWith(registry: PluginRegistry) {\n        GeneratedPluginRegistrant.registerWith(registry)\n    }\n}\n

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firebase_util.dart

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class MyApplication : FlutterApplication(), PluginRegistrantCallback {\n    override fun onCreate() {\n        super.onCreate()\n        FlutterFirebaseMessagingService.setPluginRegistrant(this)\n    }\n\n    override fun registerWith(registry: PluginRegistry) {\n        GeneratedPluginRegistrant.registerWith(registry)\n    }\n}\n

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我调用FirebaseUtil().messagingInit()根initState应用程序小部件。

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这是应用程序启动时收到的错误日志。

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E/MethodChannel#plugins.flutter.io/firebase_messaging( 6252): Failed to handle method call\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252): java.lang.NullPointerException: Attempt to invoke virtual method \'android.content.Context android.app.Activity.getApplicationContext()\' on a null object reference\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at com.alternadom.wifiiot.WifiIotPlugin.<init>(WifiIotPlugin.java:65)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at com.alternadom.wifiiot.WifiIotPlugin.registerWith(WifiIotPlugin.java:76)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at io.flutter.plugins.GeneratedPluginRegistrant.registerWith(GeneratedPluginRegistrant.java:40)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at <<package_name>>.MyApplication.registerWith(MyApplication.kt:18)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at io.flutter.plugins.firebasemessaging.FlutterFirebaseMessagingService.startBackgroundIsolate(FlutterFirebaseMessagingService.java:164)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at io.flutter.plugins.firebasemessaging.FirebaseMessagingPlugin.onMethodCall(FirebaseMessagingPlugin.java:134)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:222)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:96)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:656)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at android.os.MessageQueue.nativePollOnce(Native Method)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at android.os.MessageQueue.next(MessageQueue.java:326)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at android.os.Looper.loop(Looper.java:160)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at android.app.ActivityThread.main(ActivityThread.java:6669)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at java.lang.reflect.Method.invoke(Native Method)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)\nE/MethodChannel#plugins.flutter.io/firebase_messaging( 6252):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)\n...\nE/flutter ( 6252): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: PlatformException(error, Attempt to invoke virtual method \'android.content.Context android.app.Activity.getApplicationContext()\' on a null object reference, null)\nE/flutter ( 6252): #0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:569:7)\nE/flutter ( 6252): #1      MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:316:33)\nE/flutter ( 6252): <asynchronous suspension>\nE/flutter ( 6252): #2      FirebaseMessaging.configure (package:firebase_messaging/firebase_messaging.dart:118:16)\nE/flutter ( 6252): #3      FirebaseUtil.messagingInit (package:<<package_name>>/util/firebase_util.dart:37:15)\nE/flutter ( 6252): #4      _MainPageState.initState (package:<<package_name>>/pages/main.dart:29:20)\nE/flutter ( 6252): #5      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4068:58)\nE/flutter ( 6252): #6      ComponentElement.mount (package:flutter/src/widgets/framework.dart:3919:5)\nE/flutter ( 6252): #7      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3101:14)\nE/flutter ( 6252): #8      Element.updateChild (package:flutter/src/widgets/framework.dart:2904:12)\nE/flutter ( 6252): #9      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3961:16)\nE/flutter ( 6252): #10     Element.rebuild (package:flutter/src/widgets/framework.dart:3738:5)\nE/flutter ( 6252): #11     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2348:33)\nE/flutter ( 6252): #12     WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:760:20)\nE/flutter ( 6252): #13     RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:280:5)\nE/flutter ( 6252): #14     SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1033:15)\nE/flutter ( 6252): #15     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:975:9)\nE/flutter ( 6252): #16     SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:891:5)\nE/flutter ( 6252): #17     _rootRun (dart:async/zone.dart:1124:13)\nE/flutter ( 6252): #18     _CustomZone.run (dart:async/zone.dart:1021:19)\nE/flutter ( 6252): #19     _CustomZone.runGuarded (dart:async/zone.dart:923:7)\nE/flutter ( 6252): #20     _invoke (dart:ui/hooks.dart:249:10)\nE/flutter ( 6252): #21     _drawFrame (dart:ui/hooks.dart:207:3)\n

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$ 扑动医生 -v

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[\xe2\x9c\x93] Flutter (Channel stable, v1.9.1+hotfix.2, on Linux, locale en_IN)\n    \xe2\x80\xa2 Flutter version 1.9.1+hotfix.2 at /home/harsh/flutter\n    \xe2\x80\xa2 Framework revision 2d2a1ffec9 (3 weeks ago), 2019-09-06 18:39:49 -0700\n    \xe2\x80\xa2 Engine revision b863200c37\n    \xe2\x80\xa2 Dart version 2.5.0\n\n [\xe2\x9c\x93] Android toolchain - develop for Android devices (Android SDK version 28.0.3)\n    \xe2\x80\xa2 Android SDK at /home/harsh/Android/Sdk\n    \xe2\x80\xa2 Android NDK location not configured (optional; useful for native profiling support)\n    \xe2\x80\xa2 Platform android-28, build-tools 28.0.3\n    \xe2\x80\xa2 Java binary at: /home/harsh/android-studio/jre/bin/java\n    \xe2\x80\xa2 Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)\n    \xe2\x80\xa2 All Android licenses accepted.\n\n[\xe2\x9c\x93] Android Studio (version 3.5)\n    \xe2\x80\xa2 Android Studio at /home/harsh/android-studio\n    \xe2\x80\xa2 Flutter plugin version 39.0.3\n    \xe2\x80\xa2 Dart plugin version 191.8423\n    \xe2\x80\xa2 Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)\n\n[\xe2\x9c\x93] Connected device (1 available)\n    \xe2\x80\xa2 Android SDK built for x86 \xe2\x80\xa2 emulator-5554 \xe2\x80\xa2 android-x86 \xe2\x80\xa2 Android 9 (API 28) (emulator)\n\n\xe2\x80\xa2 No issues found!\n

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我仔细检查了README并检查了实现。我觉得不错。不知道出了什么问题？插件有什么bug吗？

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如果我不在方法onBackgroundMessage中传递参数，这个确切的代码就可以工作FirebaseMessaging.configure。

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Answer 1

您正在使用的插件之一（在本例中WifiIoTPlugin）抛出空异常。主要是因为该插件是为仅前台场景而设计的。firebase_messaging是一个也在后台工作的插件，因此这就是冲突。

当将和一起用作 时，也会引起类似的问题。android_alarm_managergoogle_maps_flutterandroid_alarm_manager

通过在没有活动时不注册插件可以快速解决此问题。检查用于解决上述问题的拉取请求。

导致问题的插件（仅前台插件）代码应如下所示：

public static void registerWith(Registrar registrar) {
        if (registrar.activity() == null) {
            // When a background flutter view tries to register the plugin, the registrar has no activity.
            // We stop the registration process as this plugin is foreground only.
            return;
        }
        final ForegroundPlugin foregroundPlugin = new ForegroundPlugin(registrar.activity()); 
        ...
}