Deserializing JSON array without a Root. How do you read the array values?

Question

I'm trying to deserialize an array using Newtonsoft so I can display the list of values but I keep getting this error no matter what I try: Exception thrown: 'System.NullReferenceException'

This is my JSON:

[
  {
    "M": {
      "ItemNo": {
        "S": "111803"
      },
      "Name": {
        "S": "Viper HD 10 x 50 RP Bi"
      },
      "Price": {
        "N": "549.99"
      },
      "Quantity": {
        "N": "1"
      }
    }
  },
  {
    "M": {
      "ItemNo": {
        "S": "111715"
      },
      "Name": {
        "S": "Cantilever / 2\" Of"
      },
      "Price": {
        "N": "89.99"
      },
      "Quantity": {
        "N": "1"
      }
    }
  }
]

This is my C# class:

public class ItemNo
{

    [JsonProperty("S")]
    public string S { get; set; }
}

public class Name
{

    [JsonProperty("S")]
    public string S { get; set; }
}

public class Price
{

    [JsonProperty("N")]
    public string N { get; set; }
}

public class Quantity
{

    [JsonProperty("N")]
    public string N { get; set; }
}

public class M
{

    [JsonProperty("ItemNo")]
    public ItemNo ItemNo { get; set; }

    [JsonProperty("Name")]
    public Name Name { get; set; }

    [JsonProperty("Price")]
    public Price Price { get; set; }

    [JsonProperty("Quantity")]
    public Quantity Quantity { get; set; }
}

public class Items
{

    [JsonProperty("M")]
    public M M { get; set; }
}

And my code to deserialize and display the first array item values but getting null reference error:

List<M> mItems = JsonConvert.DeserializeObject<List<M>>(itemsJson);
Console.WriteLine("Items Line Count: " + mItems.Count);
Console.WriteLine("Items#: " + mItems[0].ItemNo.S);
Console.WriteLine("ItemsNam: " + mItems[1].ItemName.S);
Console.WriteLine("ItemsPrc: " + mItems[3].Price.N);

Mohammed Sajid · Accepted Answer · 2020-07-03 16:53:04Z

1

You have two issues in the code :

1 - Json should be deserialized to List<Items> not List<M>
2 - mItems[3] will gives you an exception, because the collection contains just two elements.

Change the code to :

List<Items> mItems = JsonConvert.DeserializeObject<List<Items>>(json1);
Console.WriteLine("Items Line Count: " + mItems.Count);

foreach(Items item in mItems)
{
    Console.WriteLine($"No :{item.M.ItemNo.S}, Name :{item.M.Name.S}, Price :{item.M.Price.N}, Quantity :{item.M.Quantity.N}");
}

Result

Items Line Count: 2
No :111803, Name :Viper HD 10 x 50 RP Bi, Price :549.99, Quantity :1
No :111715, Name :Cantilever / 2" Of,     Price :89.99,  Quantity :1

edited Jul 3, 2020 at 16:53

answered Jul 3, 2020 at 16:47

Mohammed Sajid

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