WPApi.h

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

@interface WPApi : AFHTTPClient
+ (WPApi *)sharedApi;

- (void)getPostsWithSuccess:(void (^)(NSArray *))successBlock
                    failure:(void (^)(NSError *))failureBlock;
@end

WPApi.m

#import "WPApi.h"

#define WP_ATOM_BASE_URL @"http://en.blog.wordpress.com"

@implementation WPApi
+(WPApi *)sharedApi
{
    static WPApi *__sharedInstance;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        __sharedInstance = [[WPApi alloc] initWithBaseURL:[NSURL URLWithString:WP_ATOM_BASE_URL]];
    });
    return __sharedInstance;
}

- (void)getPostsWithSuccess:(void (^)(NSArray *))successBlock
                    failure:(void (^)(NSError *))failureBlock
{
    [self getPath:@"feed/atom/" parameters:nil
          success:^(AFHTTPRequestOperation *operation, id responseObject) {
              if (successBlock) {
                  // parse Atom XML Response
              }
          }
          failure:^(AFHTTPRequestOperation *operation, NSError *error) {
              if (failureBlock) {
                  failureBlock(error);
              }
          }];
}
@end