搜索文档并尝试一些代码后，我以以下示例为例

 AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.requestSerializer = [AFJSONRequestSerializer serializer];


NSDictionary *params = @ {@"user" :txtUserName, @"pwd" :txtPwd };


[manager POST:URL_SIGNIN parameters:params
success:^(AFHTTPRequestOperation *operation, id responseObject)
{
    NSLog(@"JSON: %@", responseObject);
}
failure:
 ^(AFHTTPRequestOperation *operation, NSError *error) {
     NSLog(@"Error: %@", error);
 }];

同样不要忘记在服务器脚本中将响应头类型设置为Application / json。