title: How do i implement delegate for flutter plugin
body: <p>I am doing test the iOS Backgroud service to get the location update. did successfully on native swift, but when I try with flutter plugin was failed, it looks like the delegated service doesn't work, following is my sample code in flutter plugin </p>
  
  <pre><code>import Flutter
  import CoreLocation
  import UIKit
  
  @available(iOS 9.0, *)
  public class SwiftSimpleBackgroundGeolocationPlugin: NSObject, FlutterPlugin, CLLocationManagerDelegate {
  
      static var channel: FlutterMethodChannel?
  
      public static func register(with registrar: FlutterPluginRegistrar) {
          let instance = SwiftSimpleBackgroundGeolocationPlugin()
  
          SwiftSimpleBackgroundGeolocationPlugin.channel = FlutterMethodChannel(name: "simple_background_geolocation", binaryMessenger: registrar.messenger())
          registrar.addMethodCallDelegate(instance, channel: SwiftSimpleBackgroundGeolocationPlugin.channel!)
          SwiftSimpleBackgroundGeolocationPlugin.channel?.setMethodCallHandler(instance.handle)
      }
  
      public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
  
          let   locationManager  = CLLocationManager()
          locationManager.delegate = self
  
          locationManager.desiredAccuracy = kCLLocationAccuracyBest
          locationManager.allowsBackgroundLocationUpdates = true
          locationManager.pausesLocationUpdatesAutomatically = false
          locationManager.requestAlwaysAuthorization()
  
          locationManager.startUpdatingLocation();
      }
  </code></pre>