No visible @interface declares the selector error

I have a connection class in my project. I want to use this class in for a lot of works. When I tried to call this class's function getting following error : No visible @interface declares the selector error

coreConnection.h

@interface coreConnection:NSArray
{
    NSData *returnData;
}
      -(NSArray*)getData;
@end

coreConnection.m

#import "coreConnection.h"

@implementation coreConnection

-(NSArray*)getData:(NSString*)link
{
    NSOperationQueue *apiCallsQueue = [[NSOperationQueue alloc] init];
    NSURL *URL = [NSURL URLWithString:link];
    NSURLRequest *request = [NSURLRequest requestWithURL:URL];
    [NSURLConnection sendAsynchronousRequest:request queue:apiCallsQueue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
        dispatch_async(dispatch_get_main_queue(), ^{
            returnData = data;
        });
    }];
    return [NSJSONSerialization JSONObjectWithData:returnData options:nil error:nil];
}
@end

viewController.m

#import "coreConnection.h"

- (void)viewDidLoad
{
    [[self headlineCollectionView]setDelegate:self];
    [[self headlineCollectionView]setDataSource:self];
     [self.headlineCollectionView registerNib:[UINib nibWithNibName:@"HeadLineCell" bundle:nil] forCellWithReuseIdentifier:@"CELL"];
    coreConnection speed=[[coreConnection alloc] init];;
    headline = [speed getData:@"string"];
    [self.headlineCollectionView reloadData];
[super viewDidLoad];
}