GeofenceServiceInit.m

- (instancetype)init:(NSObject<FlutterPluginRegistrar> *)registrar {
  self = [super init];
  NSAssert(self, @"super init cannot be nil");
  
  // 1. Retrieve NSUserDefaults which will be used to store callback handles
  // between launches.
  _persistentState = [NSUserDefaults standardUserDefaults];
  
  // 2. Initialize the location manager, and register as its delegate.
  _locationManager = [[CLLocationManager alloc] init];
  [_locationManager setDelegate:self];
  [_locationManager requestAlwaysAuthorization];
  _locationManager.allowsBackgroundLocationUpdates = YES;
  
  // 3. Initialize the Dart runner which will be used to run the callback
  // dispatcher.
  _headlessRunner = [[FlutterEngine alloc] 
                        initWithName:@"GeofencingIsolate" 
                        project:nil 
                        allowHeadlessExecution:YES];
  _registrar = registrar;
  
  // 4. Create the method channel used by the Dart interface to invoke
  // methods and register to listen for method calls.
  _mainChannel = [FlutterMethodChannel 
                  methodChannelWithName:@"plugins.flutter.io/geofencing_plugin"
                  binaryMessenger:[registrar messenger]];
  [registrar addMethodCallDelegate:self channel:_mainChannel];
  
  // 5. Create a second method channel to be used to communicate with the
  // callback dispatcher. This channel will be registered to listen for
  // method calls once the callback dispatcher is started.
  _callbackChannel =
    [FlutterMethodChannel methodChannelWithName:@"plugins.flutter.io/geofencing_plugin_background"
      binaryMessenger:_headlessRunner];
  
  return self;
}