How to post json data using AFNetworking

AFNetworking_post_json.m

NSURL *url = [NSURL URLWithString:@"http://someurl.com/"];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
// don't forget to set parameterEncoding!
httpClient.parameterEncoding = AFJSONParameterEncoding;
NSDictionary *params = @{@"key" : @"value"};
NSMutableURLRequest *request = [httpClient requestWithMethod:@"POST" path:@"" parameters:params];
AFHTTPRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:nil failure:nil];
[operation start];