C# JSON deserialize exception

Question

If I attempt to deserialize a series of classes with a root class that's derived from List or Dictionary, I get this exception:

"The value \"System.Collections.Generic.Dictionary`2[System.String,System.Object]\" is not of type \"JSONTesting.UserInformation\" and cannot be used in this generic collection.\r\nParameter name: value"

This is the code that I'm using to create the JSON file and to deserialize it. It's just a small sample project that demonstrates the issue:

    private void BuildUserInfo(object sender, EventArgs e)
    {
      Users users = new Users();
      UserInformation userInformation;

      //Item 1
      userInformation = new UserInformation();
      userInformation.Name = "John Doe";
      userInformation.Age = "50";
      userInformation.Addresses.Add(new Address("11234 Smith Pl.", "Orlando", "FL", "32789"));
      userInformation.Addresses.Add(new Address("553 Park St.", "Boston", "MA", "02115"));
      userInformation.PhoneNumbers.Add(new PhoneNumber("617", "111-2222", string.Empty));
      userInformation.PhoneNumbers.Add(new PhoneNumber("508", "236-0173", "22734"));
      users.Add(userInformation);

      //Serialize
      JavaScriptSerializer serializer = new JavaScriptSerializer();
      StreamWriter streamOut = null;
      string outString = string.Empty;

      outString = serializer.Serialize(users);
      streamOut = new StreamWriter("OUTFILE.JSON");
      streamOut.Write(outString);

      streamOut.Close();
    }

    private void ReadUserInfo(object sender, EventArgs e)
    {
      JavaScriptSerializer serializer;
      StreamReader streamIn = null;
      Users retrievedUsers = null;

      if (File.Exists("OUTFILE.JSON"))
      {
        streamIn = new StreamReader("OUTFILE.JSON");
        serializer = new JavaScriptSerializer();
        retrievedUsers = serializer.Deserialize<Users>(streamIn.ReadToEnd());

        streamIn.Close();
      }
    }
  }

  public class Users: List<UserInformation>
  {
    public UserInformation getUserByName(string name)
    {
      foreach (UserInformation user in this)
      {
        if (name == user.Name)
          return user;
      }

      return null;
    }
  }

  public class UserInformation
  {
    public string Name;
    public string Age;

    public List<Address> Addresses;
    public List<PhoneNumber> PhoneNumbers;

    public UserInformation()
    {
      Name = string.Empty;
      Age = string.Empty;
      Addresses = new List<Address>();
      PhoneNumbers = new List<PhoneNumber>();
    }

    public UserInformation(string Name, string Age)
    {
      this.Name = Name;
      this.Age = Age;
      Addresses = new List<Address>();
      PhoneNumbers = new List<PhoneNumber>();
    }
  }

  public class Address
  {
    public string Street;
    public string City;
    public string State;
    public string PostalCode;

    public Address()
    {
      Street = string.Empty;
      City = string.Empty;
      State = string.Empty;
      PostalCode = string.Empty;
    }

    public Address(string Street, string City, string State, string PostalCode)
    {
      this.Street = Street;
      this.City = City;
      this.State = State;
      this.PostalCode = PostalCode;
    }
  }

  public class PhoneNumber
  {
    public string AreaCode;
    public string Number;
    public string Extension;

    public PhoneNumber()
    {
      AreaCode = string.Empty;
      Number = string.Empty;
      Extension = string.Empty;
    }

    public PhoneNumber(string AreaCode, string Number, string Extension)
    {
      this.AreaCode = AreaCode;
      this.Number = Number;
      this.Extension = Extension;
    }
  }

This is the JSON that is generated by the BuildUserInfo function:

    [
      {
        "Name": "John Doe",
        "Age": "50",
        "Addresses": [
          {
            "Street": "11234 Smith Pl.",
            "City": "Orlando",
            "State": "FL",
            "PostalCode": "32789"
          },
          {
            "Street": "553 Park St.",
            "City": "Boston",
            "State": "MA",
            "PostalCode": "02115"
          }
        ],
        "PhoneNumbers": [
          {
            "AreaCode": "617",
            "Number": "111-2222",
            "Extension": ""
          },
          {
            "AreaCode": "508",
            "Number": "236-0173",
            "Extension": "22734"
          }
        ]
      }
    ]

If I change the Users class so that it is not derived from List and just make it a class with an internal List collection, it works fine. An example of this:

public class Users
{
  public List<UserInformation> UserItems = new List<UserInformation>();
}

What do I need to change to be able to deserialize this JSON?

Edit: Trying the link from the comment below, I changed to the following:

public class Users(IEnumerable<UserInformation> collection) : base (collection) {

}

I get build errors:

Error 1 Invalid token '(' in class, struct, or interface member declaration c:\Local .NET Projects\2010\JSONTesting1\Form1.cs 66 25 JSONTesting1 Error 2 { expected c:\Local .NET Projects\2010\JSONTesting1\Form1.cs 66 25 JSONTesting1 Error 3 ; expected c:\Local .NET Projects\2010\JSONTesting1\Form1.cs 66 69 JSONTesting1 Error 4 Invalid token ')' in class, struct, or interface member declaration c:\Local .NET Projects\2010\JSONTesting1\Form1.cs 66 93 JSONTesting1 Error 5 } expected c:\Local .NET Projects\2010\JSONTesting1\Form1.cs 153 2 JSONTesting1

Your trying to put a JSON array into a single object. Try changing the retrievedUsers to a list and then deserialize as a list List<Users> retrievedUsers = new List<Users>(); retrievedUsers = serializer.Deserialize<IList<Users>>streamIn.ReadToEnd()); — MikeS
– MikeS, Commented Feb 26, 2019 at 16:33

Anderson Pimentel · Accepted Answer · 2019-02-26 17:54:10Z

1

Do you have to use JavaScriptSerializer? If you do, there must some configuration detail we are missing, but Newtonsoft.Json handles the situation without any adjustments:

private static void BuildUserInfo()
{
    // ...

    //Serialize
    File.WriteAllText("OUTFILE.JSON", Newtonsoft.Json.JsonConvert.SerializeObject(users));
}

private static void ReadUserInfo()
{
    Users retrievedUsers = null;

    if (File.Exists("OUTFILE.JSON"))
    {
        var json = File.ReadAllText("OUTFILE.JSON");

        retrievedUsers = Newtonsoft.Json.JsonConvert.DeserializeObject<Users>(json);
    }
}

edited Feb 26, 2019 at 17:54

answered Feb 26, 2019 at 16:39

Anderson Pimentel

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2 Comments

Scott Over a year ago

I am serializing it exactly as I want it to be - the entire collection out to a JSON file. I want to deserialize it into a Users object, which is a collection of UserInformation objects. I want to bring the entire thing back into a Users object. If I change the Users class so that it is not derived from List<UserInformat>, it works fine.

Anderson Pimentel Over a year ago

Editted the answer, using Newtonsoft.Json

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