Objective C flight controller singleton

FlightController.m

@import DJISDK;

@interface RCTBridgeDJIFlightController : RCTEventEmitter<DJIFlightControllerDelegate> {
    DJIFlightControllerState *flightControllerState;
    NSString *testString;
}


@property(nonatomic, readonly) DJIFlightControllerState *flightControllerState;
@property(nonatomic, readonly) NSString *testString;

+ (id)sharedFlightController;

@end


@implementation RCTBridgeDJIFlightController

DJIFlightControllerState *flightControllerState;
NSString *testString;

@synthesize flightControllerState;
@synthesize testString;

    + (id)sharedFlightController {
        static RCTBridgeDJIFlightController *sharedFlightControllerInstance = nil;
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            sharedFlightControllerInstance = [[self alloc] init];
        });
        return sharedFlightControllerInstance;
    }

    - (id)init {
    if (self = [super init]) {
        flightControllerState = nil;
        testString = @"TEST STRING";
    }
    return self;
    }


    -(void)flightController:(DJIFlightController *)fc didUpdateState:(DJIFlightControllerState *)state {
    flightControllerState = state;
    }
@end

class VirtualStickController {
  var flightControllerSharedInstance: RCTBridgeDJIFlightController

  override init() {
      self.flightControllerSharedInstance = RCTBridgeDJIFlightController. sharedFlightController()
  }

  func getFlightControllerState() {
     if let testString = flightControllerSharedInstance.testString {
         print("\(testString)")
     } else {
         print("NOT HERE")
     }

      if let state = flightControllerSharedInstance.flightControllerState {
      print("FLIGHT CONTROLLER STATE: \(state)")
    } else {
      print ("NULL")
    }
  }