C# Check if JSON response contains key

I think there are couple of ways to handle this, like:

• Do IndexOf inside the string and decide if the property is there or not?

For example:

if (response.IndexOf("\"code\":", StringComparison.CurrentCultureIgnoreCase) > 0) /*assumption properties are inside double quotes*/
{
    //Do things for error   
}
else
{
    //Do things for success
}

• Have a class which has properties for both success and failure case and now based on the property representing the value for Error decide whether it passed or not

For example:

var instance = JsonConvert.DeserializeObject<RootObject>(response);
if (instance.code != 0)
{
    //Do things for error
}
else
{
    //Do things for success
}

I have tried to do the second option with the below code so give this code a try. I have created mock classes based on your sample data using json2csharp. I hope I have understood your question.

using Newtonsoft.Json;
using System;
using System.Collections.Generic;

namespace Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            var responses = new string[] { @"{""reason"":""unlucky"",""message"":null,""code"":460}",
            @"{""errorState"":null,""credits"":6310,""itemInfo"":[{""tradeId"":717011415,""itemData"":{""id"":101619602325
            ,""timestamp"":1447170628,""formation"":""f3412"",""untradeable"":false,""assetId"":158023,""rating"":94,""itemType""
            :""player"",""resourceId"":-2147325625,""owners"":1,""discardValue"":752,""itemState"":""forSale"",""cardsubtypeid""
            :3,""lastSalePrice"":0,""morale"":50,""fitness"":99,""injuryType"":""none"",""injuryGames"":0,""preferredPosition""
            :""RW"",""statsList"":[{""value"":0,""index"":0},{""value"":0,""index"":1},{""value"":0,""index"":2},{""value"":0,""index""
            :3},{""value"":0,""index"":4}],""lifetimeStats"":[{""value"":0,""index"":0},{""value"":0,""index"":1},{""value"":0,""index""
            :2},{""value"":0,""index"":3},{""value"":0,""index"":4}],""training"":0,""contract"":7,""suspension"":0,""attributeList""
            :[{""value"":92,""index"":0},{""value"":88,""index"":1},{""value"":86,""index"":2},{""value"":95,""index"":3},{""value""
            :24,""index"":4},{""value"":62,""index"":5}],""teamid"":241,""rareflag"":1,""playStyle"":250,""leagueId"":53,""assists""
            :0,""lifetimeAssists"":0,""loyaltyBonus"":1,""pile"":5,""nation"":52},""tradeState"":""active"",""buyNowPrice"":1726000
            ,""currentBid"":0,""offers"":0,""watched"":null,""bidState"":""none"",""startingBid"":426000,""confidenceValue"":100
            ,""expires"":3212,""sellerName"":""FIFA UT"",""sellerEstablished"":0,""sellerId"":0,""tradeOwner"":false}],""duplicateItemIdList""
            :null,""bidTokens"":{},""currencies"":[{""name"":""COINS"",""funds"":6310,""finalFunds"":6310},{""name"":""POINTS""
            ,""funds"":0,""finalFunds"":0},{""name"":""DRAFT_TOKEN"",""funds"":0,""finalFunds"":0}]}" };

            foreach (var response in responses)
            {
                var instance = JsonConvert.DeserializeObject<RootObject>(response);
                if (instance.code != 0)
                {
                    //Do things for error
                }
                else
                {   
                    //Do things for success
                }
            }
        }
    }

    public class StatsList
    {
        public int value { get; set; }
        public int index { get; set; }
    }

    public class LifetimeStat
    {
        public int value { get; set; }
        public int index { get; set; }
    }

    public class AttributeList
    {
        public int value { get; set; }
        public int index { get; set; }
    }

    public class ItemData
    {
        public long id { get; set; }
        public int timestamp { get; set; }
        public string formation { get; set; }
        public bool untradeable { get; set; }
        public int assetId { get; set; }
        public int rating { get; set; }
        public string itemType { get; set; }
        public int resourceId { get; set; }
        public int owners { get; set; }
        public int discardValue { get; set; }
        public string itemState { get; set; }
        public int cardsubtypeid { get; set; }
        public int lastSalePrice { get; set; }
        public int morale { get; set; }
        public int fitness { get; set; }
        public string injuryType { get; set; }
        public int injuryGames { get; set; }
        public string preferredPosition { get; set; }
        public List<StatsList> statsList { get; set; }
        public List<LifetimeStat> lifetimeStats { get; set; }
        public int training { get; set; }
        public int contract { get; set; }
        public int suspension { get; set; }
        public List<AttributeList> attributeList { get; set; }
        public int teamid { get; set; }
        public int rareflag { get; set; }
        public int playStyle { get; set; }
        public int leagueId { get; set; }
        public int assists { get; set; }
        public int lifetimeAssists { get; set; }
        public int loyaltyBonus { get; set; }
        public int pile { get; set; }
        public int nation { get; set; }
    }

    public class ItemInfo
    {
        public int tradeId { get; set; }
        public ItemData itemData { get; set; }
        public string tradeState { get; set; }
        public int buyNowPrice { get; set; }
        public int currentBid { get; set; }
        public int offers { get; set; }
        public object watched { get; set; }
        public string bidState { get; set; }
        public int startingBid { get; set; }
        public int confidenceValue { get; set; }
        public int expires { get; set; }
        public string sellerName { get; set; }
        public int sellerEstablished { get; set; }
        public int sellerId { get; set; }
        public bool tradeOwner { get; set; }
    }

    public class BidTokens
    {
    }

    public class Currency
    {
        public string name { get; set; }
        public int funds { get; set; }
        public int finalFunds { get; set; }
    }

    public class RootObject
    {
        public string reason { get; set; }
        public object message { get; set; }
        public int code { get; set; }


        public object errorState { get; set; }
        public int credits { get; set; }
        public List<ItemInfo> itemInfo { get; set; }
        public object duplicateItemIdList { get; set; }
        public BidTokens bidTokens { get; set; }
        public List<Currency> currencies { get; set; }

        public override string ToString()
        {
            return $"Contains Error: {code != 0}";
        }
    }
}