如何修复后台通知处理程序中的此错误？
How can i fix This error in background notification handler?
当我集成 firebase_messaging 以在后台接收通知时，应用程序出现问题
调试时出现此错误：
I/FLTFireBGExecutor(29060): Creating background FlutterEngine instance, with args: [--start-paused, --enable-dart-profiling] W/FlutterEngineCxnRegstry(29060): Attempted to register plugin (io.flutter.embedding.engine.plugins.shim.ShimPluginRegistry$ShimRegistrarAggregate@2549a44) but it was already registered with this FlutterEngine (io.flutter.embedding.engine.FlutterEngine@99e972d). E/MethodChannel#(29060): Parameter messenger must not be null. I/BlockMonitor(29060): dispatchingThrewException In MainThread D/AndroidRuntime(29060): Shutting down VM I/QarthLog(29060): [PatchStore] createDisableExceptionQarthFile I/QarthLog(29060): [PatchStore] create disable file for com.dgmsolutions.foolivery uid is 10523 E/AndroidRuntime(29060): FATAL EXCEPTION: main E/AndroidRuntime(29060): java.lang.NullPointerException: Attempt to invoke interface method 'void io.flutter.plugin.common.BinaryMessenger.setMessageHandler(java.lang.String, io.flutter.plugin.common.BinaryMessenger$BinaryMessageHandler)' on a null object reference E/AndroidRuntime(29060): at io.flutter.plugin.common.MethodChannel.setMethodCallHandler(MethodChannel.java:119) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingPlugin.initInstance(FlutterFirebaseMessagingPlugin.java:64) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingPlugin.registerWith(FlutterFirebaseMessagingPlugin.java:58) E/AndroidRuntime(29060): at com.dgmsolutions.foolivery.Application.registerWith(Application.kt:16) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingBackgroundExecutor.lambda$null[=10=]$FlutterFirebaseMessagingBackgroundExecutor(FlutterFirebaseMessagingBackgroundExecutor.java:206) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.-$$Lambda$FlutterFirebaseMessagingBackgroundExecutor$e4cdQ2b1x-adsVcO-hA2dn2VM8E.run(Unknown Source:6) E/AndroidRuntime(29060): at android.os.Handler.handleCallback(Handler.java:888) E/AndroidRuntime(29060): at android.os.Handler.dispatchMessage(Handler.java:100) E/AndroidRuntime(29060): at android.os.Looper.loop(Looper.java:213) E/AndroidRuntime(29060): at android.app.ActivityThread.main(ActivityThread.java:8178) E/AndroidRuntime(29060): at java.lang.reflect.Method.invoke(Native Method) E/AndroidRuntime(29060): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513) E/AndroidRuntime(29060): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101) I/Process (29060): Sending signal. PID: 29060 SIG: 9 Lost connection to device.
我的代码（图中）
main class
application.kt
manifest.xml
notification class
因为你是 运行 Flutter 2.0.1，你只需要配置 firebase 消息插件的 Flutter 部分，并添加你的 google-services.json 文件。
仔细阅读官方文档，你的问题就会得到解决:)
如果您需要展示如何实现 Firebase 通知的示例项目，可以查看 at this one
当我集成 firebase_messaging 以在后台接收通知时，应用程序出现问题 调试时出现此错误：
I/FLTFireBGExecutor(29060): Creating background FlutterEngine instance, with args: [--start-paused, --enable-dart-profiling] W/FlutterEngineCxnRegstry(29060): Attempted to register plugin (io.flutter.embedding.engine.plugins.shim.ShimPluginRegistry$ShimRegistrarAggregate@2549a44) but it was already registered with this FlutterEngine (io.flutter.embedding.engine.FlutterEngine@99e972d). E/MethodChannel#(29060): Parameter messenger must not be null. I/BlockMonitor(29060): dispatchingThrewException In MainThread D/AndroidRuntime(29060): Shutting down VM I/QarthLog(29060): [PatchStore] createDisableExceptionQarthFile I/QarthLog(29060): [PatchStore] create disable file for com.dgmsolutions.foolivery uid is 10523 E/AndroidRuntime(29060): FATAL EXCEPTION: main E/AndroidRuntime(29060): java.lang.NullPointerException: Attempt to invoke interface method 'void io.flutter.plugin.common.BinaryMessenger.setMessageHandler(java.lang.String, io.flutter.plugin.common.BinaryMessenger$BinaryMessageHandler)' on a null object reference E/AndroidRuntime(29060): at io.flutter.plugin.common.MethodChannel.setMethodCallHandler(MethodChannel.java:119) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingPlugin.initInstance(FlutterFirebaseMessagingPlugin.java:64) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingPlugin.registerWith(FlutterFirebaseMessagingPlugin.java:58) E/AndroidRuntime(29060): at com.dgmsolutions.foolivery.Application.registerWith(Application.kt:16) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingBackgroundExecutor.lambda$null[=10=]$FlutterFirebaseMessagingBackgroundExecutor(FlutterFirebaseMessagingBackgroundExecutor.java:206) E/AndroidRuntime(29060): at io.flutter.plugins.firebase.messaging.-$$Lambda$FlutterFirebaseMessagingBackgroundExecutor$e4cdQ2b1x-adsVcO-hA2dn2VM8E.run(Unknown Source:6) E/AndroidRuntime(29060): at android.os.Handler.handleCallback(Handler.java:888) E/AndroidRuntime(29060): at android.os.Handler.dispatchMessage(Handler.java:100) E/AndroidRuntime(29060): at android.os.Looper.loop(Looper.java:213) E/AndroidRuntime(29060): at android.app.ActivityThread.main(ActivityThread.java:8178) E/AndroidRuntime(29060): at java.lang.reflect.Method.invoke(Native Method) E/AndroidRuntime(29060): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513) E/AndroidRuntime(29060): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101) I/Process (29060): Sending signal. PID: 29060 SIG: 9 Lost connection to device.
我的代码（图中） main class
application.kt
manifest.xml
notification class
因为你是 运行 Flutter 2.0.1，你只需要配置 firebase 消息插件的 Flutter 部分，并添加你的 google-services.json 文件。
仔细阅读官方文档，你的问题就会得到解决:)
如果您需要展示如何实现 Firebase 通知的示例项目，可以查看 at this one