nslog return null

ClassHelper.h
#import <Foundation/Foundation.h>

@interface ClassHelperModel : NSObject
+ (NSDictionary*)getData:(NSString*)serverURL;
@end
-----------------------------------------------------------------------------------------------------------------------------------

ClassHelper.m

#import "ClassHelperModel.h"
#import <AFNetworking/AFNetworking.h>

NSDictionary *dataDict;

@implementation ClassHelperModel
+ (NSDictionary*)getData:(NSString *)serverURL {
    NSString *dataAPILink = [[NSString alloc] initWithFormat:@"http://%@/data.php", serverURL];
    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    [manager GET:dataAPILink
      parameters:nil
         success:^(AFHTTPRequestOperation *operation, id responseObject) {
             dataDict = [[NSDictionary alloc] initWithDictionary:responseObject];
		// when i nslog here i can see the data
		NSLog("hello data : %@, dataDict");
         } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
             NSLog(@"data Error: %@", error);
             if (error) {
                 UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"System Down" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
                 [alert show];
             }
        }];

    // when i nslog here, i cannot see the data
    NSLog(@"hello world : %@", sebaranDict);
    return sebaranDict;
}
@end
-----------------------------------------------------------------------------------------------------------------------------------
MainVC.m

#import "MainVC.h"
#import "ClassHelperModel.h"

@interface SebaranVC ()
@property (strong, nonatomic) NSDictionary *dataDictionary;
@end

@implementation SebaranVC
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

//    dataDictionary = [[NSDictionary alloc] init];
    dataDictionary = [ClassHelperModel getData:@"127.0.0.1"];
	// I got null here, IDK why :(
    NSLog(@"Data Dictionary: %@", dataDictionary);
}