C#. How to parse the response from the server into classes?

Question

C++ / C#

Good afternoon!
I'm making a web handler.
The server sends a POST request to it with the following test content:

CONTENT

Content:
{
  "subscriptionId": "00000000-0000-0000-0000-000000000000",
  "notificationId": 52,
  "id": "d2d46fb1-dba5-403c-9373-427583f19e8c",
  "eventType": "workitem.created",
  "publisherId": "tfs",
  "message": {
    "text": "Bug #5 (Some great new idea!) created by Jamal Hartnett.\r\n(http://fabrikam-fiber-inc.visualstudio.com/web/wi.aspx?pcguid=74e918bf-3376-436d-bd20-8e8c1287f465&id=5)",
    "html": "<a href=\"http://fabrikam-fiber-inc.visualstudio.com/web/wi.aspx?pcguid=74e918bf-3376-436d-bd20-8e8c1287f465&amp;id=5\">Bug #5</a> (Some great new idea!) created by Jamal Hartnett.",
    "markdown": "[Bug #5](http://fabrikam-fiber-inc.visualstudio.com/web/wi.aspx?pcguid=74e918bf-3376-436d-bd20-8e8c1287f465&id=5) (Some great new idea!) created by Jamal Hartnett."
  },
  "detailedMessage": {
    "text": "Bug #5 (Some great new idea!) created by Jamal Hartnett.\r\n(http://fabrikam-fiber-inc.visualstudio.com/web/wi.aspx?pcguid=74e918bf-3376-436d-bd20-8e8c1287f465&id=5)\r\n\r\n- Area: FabrikamCloud\r\n- Iteration: FabrikamCloud\\Release 1\\Sprint 1\r\n- State: New\r\n- Assigned to: \r\n- Comment: \r\n- Severity: 3 - Medium\r\n",
    "html": "<a href=\"http://fabrikam-fiber-inc.visualstudio.com/web/wi.aspx?pcguid=74e918bf-3376-436d-bd20-8e8c1287f465&amp;id=5\">Bug #5</a> (Some great new idea!) created by Jamal Hartnett.<ul>\r\n<li>Area: FabrikamCloud</li>\r\n<li>Iteration: FabrikamCloud\\Release 1\\Sprint 1</li>\r\n<li>State: New</li>\r\n<li>Assigned to: </li>\r\n<li>Comment: </li>\r\n<li>Severity: 3 - Medium</li></ul>",
    "markdown": "[Bug #5](http://fabrikam-fiber-inc.visualstudio.com/web/wi.aspx?pcguid=74e918bf-3376-436d-bd20-8e8c1287f465&id=5) (Some great new idea!) created by Jamal Hartnett.\r\n\r\n* Area: FabrikamCloud\r\n* Iteration: FabrikamCloud\\Release 1\\Sprint 1\r\n* State: New\r\n* Assigned to: \r\n* Comment: \r\n* Severity: 3 - Medium\r\n"
  },
  "resource": {
    "id": 5,
    "rev": 1,
    "fields": {
      "System.AreaPath": "FabrikamCloud",
      "System.TeamProject": "FabrikamCloud",
      "System.IterationPath": "FabrikamCloud\\Release 1\\Sprint 1",
      "System.WorkItemType": "Bug",
      "System.State": "New",
      "System.Reason": "New defect reported",
      "System.CreatedDate": "2014-07-15T17:42:44.663Z",
      "System.CreatedBy": "Jamal Hartnett",
      "System.ChangedDate": "2014-07-15T17:42:44.663Z",
      "System.ChangedBy": "Jamal Hartnett",
      "System.Title": "Some great new idea!",
      "Microsoft.VSTS.Common.Severity": "3 - Medium",
      "WEF_EB329F44FE5F4A94ACB1DA153FDF38BA_Kanban.Column": "New"
    },
    "_links": {
      "self": {
        "href": "http://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/workItems/5"
      },
      "workItemUpdates": {
        "href": "http://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/workItems/5/updates"
      },
      "workItemRevisions": {
        "href": "http://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/workItems/5/revisions"
      },
      "workItemType": {
        "href": "http://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/ea830882-2a3c-4095-a53f-972f9a376f6e/workItemTypes/Bug"
      },
      "fields": {
        "href": "http://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/fields"
      }
    },
    "url": "http://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/workItems/5"
  },
  "resourceVersion": "1.0",
  "resourceContainers": {
    "collection": {
      "id": "c12d0eb8-e382-443b-9f9c-c52cba5014c2"
    },
    "account": {
      "id": "f844ec47-a9db-4511-8281-8b63f4eaf94e"
    },
    "project": {
      "id": "be9b3917-87e6-42a4-a549-2bc06a7a878f"
    }
  },
  "createdDate": "2018-12-12T11:05:32.7964707Z"
}

For my part, I want to parse this content into classes and then deal with event processing.
But from my side, and when sending a POST from the server, I get an error:
System.NullReferenceException: "Object reference not set to an instance of an object."
WebApplication8.Controllers.Content.Resource.get returned null.
Code below.

THE CODE

namespace WebApplication8.Controllers
{
    [Route("api/[controller]")]
    public class ServiceHookEventController : Controller
    {
        // POST: /ServiceHookEvent/workitemcreated
        [HttpPost]
        public HttpResponseMessage WorkItemCreated(Content workItemEvent)
        {

            //Grabbing the title for the new workitem
            var value = RetrieveFieldValue("System.Title", workItemEvent.Resource.Fields);
            //Acknowledge event receipt
            return new HttpResponseMessage(HttpStatusCode.OK);
        }


        public String RetrieveFieldValue(String key, IList<FieldInfo> fields)
        {
            if (String.IsNullOrEmpty(key))
                return String.Empty;

            var result = fields.Single(s => s.Field.RefName == key);

            if (result == null)
                return String.Empty;

            return result.Value;
        }

    }

    public class Content
    {
        public String SubscriptionId { get; set; }

        public int NotificationId { get; set; }

        public String EventType { get; set; }

        public WorkItemResource Resource { get; set; }

    }

    public class WorkItemResource
    {
        public IList<FieldInfo> Fields { get; set; }

        public int Id { get; set; }

        public int Rev { get; set; }

        public String Url { get; set; }
    }

    public class FieldInfo
    {
        public FieldDetailedInfo Field { get; set; }

        public String Value { get; set; }

    }

    public class FieldDetailedInfo
    {
        public int Id { get; set; }

        public String Name { get; set; }

        public String RefName { get; set; }
    }

}

How to parse the response from the server into classes? Any ideas comrades? thanks in advance

Answer 1

Use https://www.newtonsoft.com/json
How to use I gave an answer here in this question: How to correctly describe the class for the Newtonsoft.Json C# library?