ios - 由于防止变量为@(null)，我如何避免崩溃？

Question

当应用程序执行时，我正在获取用户位置，如果位置变量为@(null)，我会阻止该 if 语句。在我的 FirstViewController.h 中：

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self;
    locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;
    [locationManager startUpdatingLocation];

}

CLLocationManager *locationManager;

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    CLLocation *currentLocation = newLocation;
    if (currentLocation != NULL) {
        [(AppDelegate *)[[UIApplication sharedApplication] delegate] setLatitude:[NSString stringWithFormat:@"%.8f", currentLocation.coordinate.latitude]];

        [(AppDelegate *)[[UIApplication sharedApplication] delegate] setLongitude:[NSString stringWithFormat:@"%.8f", currentLocation.coordinate.longitude]];
    }
}

在我的 SecondViewController：

-(void) GettingGlobalVariables{
    NSString *UsersCurrentLatitude = [(AppDelegate *)[[UIApplication sharedApplication] delegate] latitude];
    NSString *UsersCurrentLongitude = [(AppDelegate *)[[UIApplication sharedApplication] delegate] longitude];

    NSNumberFormatter * singsingsing = [[NSNumberFormatter alloc] init];
    [singsingsing setNumberStyle:NSNumberFormatterDecimalStyle];
    NSNumber * myNumberLatitude = [singsingsing numberFromString:UsersCurrentLatitude];


    NSNumberFormatter * sheCameToMeOneMorning = [[NSNumberFormatter alloc] init];
    [sheCameToMeOneMorning setNumberStyle:NSNumberFormatterDecimalStyle];
    NSNumber * myNumberLongitude = [sheCameToMeOneMorning numberFromString:UsersCurrentLongitude];
        NSLog(@"mynumberlatitude:%@,mynumberlongitude:%@",myNumberLongitude,myNumberLatitude);
    if (!myNumberLatitude) {
        NSLog(@"location variables are null");
        TabBar *TB =[[TabBar alloc]init];
        [TB performSelector:@selector(viewDidLoad)];
        [TB performSelector:@selector(locationManager:didUpdateToLocation:fromLocation:)];
        [self performSelector:@selector(GettingGlobalVariables)];

    }
}

使用这个 if 语句，当变量为空时应用程序崩溃。有什么建议吗？

Answer 1

像这样使用，

    if (currentLocation != [NSNull null] | currentLocation !=nil) {
         //write your code here.
    }