Asp.net return json response

Question

I am developing a web service , in which i need to return user type objects as json response. But i am unable to achieve it using this code.

public class BioMatricUsers : System.Web.Services.WebService {
    public BioMatricUsers()
    {
    }
    public class my_user
    {
        public my_user(string i, string b, string l)
        {
            id = i;
            badgeNumber = b;
            login = l;
        }

        public string id { get; set; }
        public string badgeNumber { get; set; }
        public string login { get; set; }
    }

    [WebMethod]
    [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
    public string GetUsers() 
    {
        OleDbConnection co = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\confiz\Desktop\att2000.mdb");
        co.Open();
        OleDbCommand cmd = new OleDbCommand("SELECT * FROM USERINFO", co);
        OleDbDataReader reader = cmd.ExecuteReader();
        string jsonString = "";
        int i = 1;
        MemoryStream ms = new MemoryStream();
        my_user user = null;

        Type type = user.GetType();


        while (reader.Read() && i <= 2)
        {
            DataContractJsonSerializer serializer = new DataContractJsonSerializer(user.GetType());
            user = new my_user(reader["USERID"].ToString(), reader["badgenumber"].ToString(), reader["SSN"].ToString());
            serializer.WriteObject(ms, user);
            jsonString = Encoding.Default.GetString(ms.ToArray());
            i++;
        }
        ms.Close();
        co.Close();
        return jsonString;  
     }
}

i am getting null reference error at this line. DataContractJsonSerializer serializer = new DataContractJsonSerializer(user.GetType())

Jude Fisher · Accepted Answer · 2012-10-01 11:44:57Z

It's because your user is null:

my_user user = null;

try:

    while (reader.Read() && i <= 2)
    {
        DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(my_user));
        user = new my_user(reader["USERID"].ToString(), reader["badgenumber"].ToString(), reader["SSN"].ToString());
        serializer.WriteObject(ms, user);
        jsonString = Encoding.Default.GetString(ms.ToArray());
        i++;
    }

Object.getType() requires a non-null object instance to work on.

typeof(Class) can be used with a class.

See here: http://msdn.microsoft.com/en-us/library/58918ffs%28v=vs.71%29.aspx

While there are other libraries which have additional features, it's perfectly acceptable to use DataContractJsonSerializer if that meets your needs

george.zakaryan · Accepted Answer · 2012-10-01 11:24:01Z

0

You need a library that serializes/deserializes objects to/from json. Here's a good one for .Net http://james.newtonking.com/projects/json-net.aspx

The samples on the web page will explain everything.

answered Oct 1, 2012 at 11:24

george.zakaryan

9801 gold badge6 silver badges18 bronze badges

1 Comment

Jude Fisher Over a year ago

But it's not necessary, and it won't solve user1673005's null reference error.

Collectives™ on Stack Overflow

Asp.net return json response

2 Answers 2

Comments

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Related