iOS平台MAUI Plugin.Firebase获取FCM Token时出现空引用异常求助

抛出的异常 #

System.NullReferenceException: Object reference not set to an instance of an object.
at Plugin.Firebase.CloudMessaging.FirebaseCloudMessagingImplementation.GetTokenAsync()

我的FCM Token代码： #

await CrossFirebaseCloudMessaging.Current.CheckIfValidAsync();
var token = await CrossFirebaseCloudMessaging.Current.GetTokenAsync();

可能遗漏的iOS配置项 #

• Firebase初始化验证
  确保在MauiProgram.cs中正确初始化Cloud Messaging模块：

  builder.AddFirebaseCloudMessaging();
  

  同时确认GoogleService-Info.plist已添加到iOS项目，且生成操作设置为BundleResource，文件内的GCM_SENDER_ID、PROJECT_ID与FCM控制台完全一致。

• AppDelegate补充FCM回调实现
  目前仅添加了DynamicLinks的处理代码，还需补充FCM相关的通知回调：

  using Plugin.Firebase.CloudMessaging;
  
  public override void RegisteredForRemoteNotifications(UIApplication application, NSData deviceToken)
  {
      FirebaseCloudMessagingImplementation.RegisteredForRemoteNotifications(application, deviceToken);
  }
  
  public override void FailedToRegisterForRemoteNotifications(UIApplication application, NSError error)
  {
      FirebaseCloudMessagingImplementation.FailedToRegisterForRemoteNotifications(application, error);
  }
  
  public override void DidReceiveRemoteNotification(UIApplication application, NSDictionary userInfo, Action<UIBackgroundFetchResult> completionHandler)
  {
      FirebaseCloudMessagingImplementation.DidReceiveRemoteNotification(application, userInfo, completionHandler);
  }
  

  另外需要在FinishedLaunching中主动请求通知权限：

  public override bool FinishedLaunching(UIApplication app, NSDictionary options)
  {
      UNUserNotificationCenter.Current.RequestAuthorization(UNAuthorizationOptions.Alert | UNAuthorizationOptions.Badge | UNAuthorizationOptions.Sound, (granted, error) => {
          if (granted)
          {
              UIApplication.SharedApplication.RegisterForRemoteNotifications();
          }
      });
      return base.FinishedLaunching(app, options);
  }
  

• 版本兼容性检查
  确认Plugin.Firebase使用最新稳定版，同时MAUI SDK版本与插件版本兼容，旧版本插件存在iOS平台初始化不完整导致空引用的问题。

是否为已知问题 #

该空引用异常是Plugin.Firebase在iOS平台上的常见问题，多数情况与Firebase Cloud Messaging实例未正确初始化、缺少必要的系统通知回调、或GoogleService-Info.plist配置错误有关，补充上述配置后通常可解决。

内容的提问来源于stack exchange，提问作者Matthew Pans