Flutter event channel: how to detect apple pencil double tap event in flutter

Question

I'm new in flutter. I'm now developing a drawing app in flutter, which uses apple pencil.

I want user can change to eraser mode when they double-tap the apple pencil. I have already developed specific drawing features, so I do not want to use plug-in such as pencil kit. Rather, I want to use event channel to directly communicate with IOS, but I'm not familiar with the feature.

I believe it is not working because the pencil interaction is a view interaction but I do not have view?

@ ios/Runner/AppDelegate.swift:

<i>
import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
  
 
    if #available(iOS 12.1, *) {
      GeneratedPluginRegistrant.register(with: self)
      FlutterEventChannel(name: "applePencilSideTouch", binaryMessenger: (window?.rootViewController as! FlutterViewController).binaryMessenger).setStreamHandler(PencilStreamHandler())

      }


    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}




@available(iOS 12.1, *)
 class PencilStreamHandler:FlutterViewController , FlutterStreamHandler, UIPencilInteractionDelegate {
     
     
     override func viewDidLoad() {
       super.viewDidLoad()
         let pencilInteraction = UIPencilInteraction()
         pencilInteraction.delegate = self
         view.addInteraction(pencilInteraction)

     }
     
    var events : FlutterEventSink?
    func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink) -> FlutterError? {
        self.events = events    
        let pencilInteraction = UIPencilInteraction()
        pencilInteraction.delegate = self
        view.addInteraction(pencilInteraction)
        print("interactionAdded")
      
        NotificationCenter.default.addObserver(self, selector: #selector(self.pencilDidDoubleTap),name: Notification.Name("PencilInteractionEvent"),object: nil)
        return nil
    }
    
    func onCancel(withArguments arguments: Any?) -> FlutterError? {
        self.events = nil
        return nil
    }
    
 func pencilInteractionDidTap(_ interaction: UIPencilInteraction) {
    NotificationCenter.default.post(name: Notification.Name("PencilInteractionEvent"), object: true)
}
}
</i>

in flutter,

  final EventChannel _stateChannel = const EventChannel("applePencilSideTouch");
 void initState() {
    super.initState();
    _stateChannel.receiveBroadcastStream().listen((event) {
       // apple pencil side double tap receiver (toggle eraser mode)
    });
</i>