C#: JSON Serialization of List returns empty array?

Question

So, I have a custom class 'User' like this:

class User
    {
        string firstname;
        string lastname;
        string proposedname;
        public User(string firstname, string lastname)
        {
            this.firstname = firstname;
            this.lastname = lastname;
            this.proposedname = $"{firstname}.{lastname}".ToLower();
        }
}

And another Class "UserCreator that has a method "GenerateList" and a method "WriteList" as well as a field which is simply a List :

public class UserCreator
    {
        internal List<User> Users;
        public UserCreator(int n = 1000)
        {
            Users = new List<User>();
            this.GenerateList(n);
        }
       public  void WriteList(string outputPath)
        {
            string json = Newtonsoft.Json.JsonConvert.SerializeObject(this.Users, Newtonsoft.Json.Formatting.Indented);
            System.IO.File.WriteAllText(outputPath, json);

        }

        void GenerateList(int amount)
        {
            List<User> result = new List<User>();
            ///...
            this.Users = result;
        }
    }

Everything works just fine until it get's to the Serialization part in WriteList(). Instead of working as Intended I get something like this:

[
  {},
  {},
  {},
  {},
  {},
  {},
  {},
  {}
]

I'm guessing it has to do with the fact that I'm using a List of a custom Class. Is that a known limitation of Newtonsoft.Json? Or maybe due to Access modifiers?

Your properties should look like this `public string firstname { get; set; }` — Equalsk, Mar 08 '18 at 15:33
Possible duplicate of [Newtonsoft.Json serialization returns empty json object](https://stackoverflow.com/questions/29003215/newtonsoft-json-serialization-returns-empty-json-object) — Drag and Drop, Mar 08 '18 at 15:51

Yannick Meeus · Accepted Answer · 2021-12-30T13:06:42.163

How you have declared your class is completely encapsulating all of your User data.

Instead of properties, those are instance fields (or class members, if we're being picky), and by default these are private. Instead, take care of your access modifiers and at least expose a public getter for every property, like so:

public class User
{
    public string firstname { get; private set;}
    public string lastname { get; private set;}
    public string proposedname { get ; private set; }
    public User(string firstname, string lastname)
    {
        this.firstname = firstname;
        this.lastname = lastname;
        this.proposedname = $"{firstname}.{lastname}".ToLower();
    }
}

score 1 · Answer 2 · answered Mar 08 '18 at 15:50

1

by default access level is private, hence your firstName, lastName, proposedName are all private fields. You can either change this to public. Or you can also write your customcontractresolver for the jsonserialzation settings.

answered Mar 08 '18 at 15:50

Liju L

124
1
4

C#: JSON Serialization of List returns empty array?

2 Answers2