Json.NET, Unable to de-serialize nullable type.

Question

I'm trying to convert JSON to C# object using Json.NET. The object looks like this in C#:

public class MyObject 
{
   public int? integerValue {get;set;}
   public DateTime? dateTimeValue {get;set;}
}

But when I run JsonConvert.DeserializeObject() on the incoming JSON, I get the following Exception:

Unable to find a constructor to use for type System.Nullable`1[System.Int32]. A class should either have a default constructor or only one constructor with arguments.

--- EDIT ----

Well it turns out that after doing many tests, the problem boils down to that my input for my JSON was like this:

{integerValue:{}, dateTimeValue: {} }

instead of:

{integerValue: null, dateTimeValue: null}

It turns out that the {} is a valid way of representing a null object in JSON but the JSON.Net parser did not know to treat {} tokens the same way as 'null' when de-serializing.

Thanks everyone for your input!

Answer 1

I dont know is it right answer or not, but at least You can create custom converter for Nullable<>, it helps me a lot with DataRow serializing/deserializing it also does not have default constructor. Here is sample

Answer 2

Hi Roberto,

The error is telling you that it cant find a a constructor that it can use for the deserialization.

Try adding a default constructor to the class:

public class MyObject
    {
        public int? integerValue { get; set; }
        public DateTime? dateTimeValue { get; set; }

        public MyObject(){}
    } 

Patrick.

--EDIT--

So I've just created a simple console app using your MyObject, with and without a default constructor and I'm getting no errors. Here is my example:

   class Program
    {
        static void Main(string[] args)
        {
            var mo = new MyObject { integerValue = null, dateTimeValue = null };
            var ser = Newtonsoft.Json.JsonConvert.SerializeObject(mo);
            var deser = Newtonsoft.Json.JsonConvert.DeserializeObject(ser, typeof(MyObject));
        }
    }

    public class MyObject
    {
        public int? integerValue { get; set; }
        public DateTime? dateTimeValue { get; set; }        
    }  

I get no exceptions...

Can you show an example of the JSON that you are trying to deserialize?