Question

Consider the following tutorial: http://blogs.msdn.com/b/rakkimk/archive/2009/01/30/asp-net-json-serialization-and-deserialization.aspx

{
    "firstName" : "Rakki",
    "lastName" : "Muthukumar",
    "department" : "Microsoft PSS",
    "address" : {
        "addressline1" : "Microsoft India GTSC",
        "addressline2" : "PSS - DSI",
        "city" : "Bangalore",
        "state" : "Karnataka",
        "country" : "India",
        "pin" : 560028
    },
"technologies" : ["IIS", "ASP.NET", "JavaScript", "AJAX"]    
}

For the json code I have the following class:

    public class Address
{
public string addressline1 { get; set; }
public string addressline2 { get; set; }
public string city { get; set; }
public string state { get; set; }
public string country { get; set; }
public int pin { get; set; }
}

public class RootObject
{
public string firstName { get; set; }
public string lastName { get; set; }
public string department { get; set; }
public Address address { get; set; }
public List<string> technologies { get; set; }
}

The above properties give me error when I’m trying to set data like

RootObjectClsObject.address.addressline1 = "NO";

It throws me NullReferrenceException. If I modify the line

public List<string> technologies { get;set;}

by following line

public List<string> technologies = new List<string>();

Which I don’t want to use. Because I’ve complex types of JSON which can’t processed in this way.

Answer 1

You are not initialising your sub-objects. The address property has not been assigned an instance of the Address object yet, so when you are attempting to update the address1 property; the application does not know which object you are referring to – hence the error.

You simply need to assign a value to the address property or initialise it with a default value.

The simplest way to do this would be in the default constructor for you RootObject class.

public class RootObject
{
   public RootObject()
   {
      address = new Address();
      technologies = new List<string>();
   }

    public string firstName { get; set; }
    public string lastName { get; set; }
    public string department { get; set; }
    public Address address { get; set; }
    public List<string> technologies { get; set; }
}