Simple example of using NSURLSession - Objective-C

Network.m

#import "CCNetwork.h"

@implementation CCNetwork

+(void) retrieveJSONAtLocation: (NSString *) urlString completionHandler: (void (^)(NSData *data, NSURLResponse *response, NSError *error)) handler {
    NSURL *url = [[NSBundle mainBundle] URLForResource:urlString withExtension:@"json"];
    [CCNetwork retrieveJSONAtURL:url completionHandler:handler];
}

+(void) retrieveJSONAtURL: (NSURL *) url completionHandler: (void (^)(NSData *data, NSURLResponse *response, NSError *error)) handler {

    NSURLSessionConfiguration *conf = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *sessionWithoutADelegate = [NSURLSession sessionWithConfiguration:conf];
    
    NSURLSessionDataTask * task = [sessionWithoutADelegate dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

        // convert to an object
        NSError * jsonError;
        NSDictionary * jsonObject = (NSDictionary *)[NSJSONSerialization JSONObjectWithData:data
                                                                                    options:NSJSONReadingAllowFragments
                                                                                      error: &jsonError];
        // save to database
        [CCDatabase saveJSONObject:jsonObject];
      
        handler(data, response, error);
        [sessionWithoutADelegate finishTasksAndInvalidate];
        
    }];
    
    [task resume];
}

@end