把text/html這種json序列化(serializer)成二進(jìn)制格式(NSData)失息，然后再解析出來(lái)譬淳，就是用NSData當(dāng)中間層。
AFHTTPSessionManager *client = [[AFHTTPSessionManager alloc] init];
client.requestSerializer = [AFHTTPRequestSerializer serializer];
client.responseSerializer = [AFHTTPResponseSerializer serializer];
拿到responseObject后盹兢，如果外層是字典：
NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:responseObject options:NSJSONReadingMutableContainers error:nil];
