如何在flutter iOS原生代码(Swift)中使用多个EventChannel

final eventChannelA = EventChannel('event_channel_a');
final eventChannelB = EventChannel('event_channel_b');

import Flutter

// ...

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // ...

    let controller : FlutterViewController = window?.rootViewController as! FlutterViewController

    let eventChannelA = FlutterEventChannel(name: "event_channel_a", binaryMessenger: controller.binaryMessenger)
    eventChannelA.setStreamHandler(EventChannelHandlerA())

    let eventChannelB = FlutterEventChannel(name: "event_channel_b", binaryMessenger: controller.binaryMessenger)
    eventChannelB.setStreamHandler(EventChannelHandlerB())

    // ...

    return true
}

import Flutter

class EventChannelHandlerA: NSObject, FlutterStreamHandler {
    private var eventSink: FlutterEventSink?

    func onListen(withArguments arguments: Any?, eventSink: @escaping FlutterEventSink) -> FlutterError? {
        self.eventSink = eventSink
        // 在此处添加处理事件A的逻辑
        return nil
    }

    func onCancel(withArguments arguments: Any?) -> FlutterError? {
        self.eventSink = nil
        // 在此处添加取消事件A的逻辑
        return nil
    }
}