gistfile1.m

- (MKNetworkOperation*) updateUser: (MDUser*) user
                            avatar: (UIImage*) avatar
                      onCompletion: (DictResponseBlock) completionBlock
                           onError: (MKNKErrorBlock) errorBlock
{
    MKNetworkOperation *op = [self operationWithPath:[NSString stringWithFormat:@"users/%@/avatar", user.uid]
                                              params:nil
                                          httpMethod:@"POST"];
    
    //    [op addData:UIImagePNGRepresentation(user.avatar) forKey:@"avatar" mimeType:@"image/png"];
    [op addData:UIImagePNGRepresentation(avatar) forKey:@"avatar" mimeType:@"image/png" fileName:@"avatar.png"];

    [op setUsername:ApplicationDelegate.user.email password:ApplicationDelegate.user.accessToken];
    [op onCompletion: [self responseBlock:completionBlock] onError: [self errorBlock]];
    
    
    [self enqueueOperation:op];
    
    return op;    
}