c# method won't add to list in class

Question

I am new to c# programming and I have a method as follows:

public void GuessTheHiddenDigits(List<int> list)
        {
            GuessingGame playerGuess = new GuessingGame();
            if(playerGuess.Guesses == null){
                playerGuess.Guesses = list;
            }
            playerGuess.Guesses = list;

        }

I wish to add my List list to the following:

public List<int> Guesses { get; set; }

Would someone be able to explain to me why it isnt adding my list accordingly?

Would someone also be able to point me in the right direction?

EDIT 1: GuessingGame class is as follows

public class GuessingGame
    {

        public List<int> Target { get; set; }
        public List<int> Guesses { get; set; } // I need this to be set during the GuessTheHiddenDigits

        public List<Guess> ShowGuessesMade()
        {
            var listRange = new List<Guess>();

            if (listRange != null)
            {
                return listRange;
            }
            return listRange;
        }

        public void NewGame()
        {
            throw new NotImplementedException();
        }


        public void GuessTheHiddenDigits(List<int> list)
        {
            GuessingGame playerGuess = new GuessingGame();
            playerGuess.Guesses = new List<int>();
            playerGuess.Guesses.AddRange(list);

        }
    }

Edit 2: unit test - my current public List Guesses is set to null, the list is getting passed in my method, debugging shows me that much. It just isn't setting the property.

 [TestMethod]
        public void GuessTheHiddenDigitsAddsTheSubmittedGuessToTheListOfGuesses()
        {
            var theGame = new GuessingGame();
            /* NOTE : The next line forces us to add a behaviour to the GuessingGame
             * class: the GuessTheHiddenDigits() method.  
             * */
            theGame.GuessTheHiddenDigits(new List<int>() { 1, 2, 3 });
            var theContext = new FakeHttpContext();
            var theKey = "GameState";
            theContext.Session.Add(theKey, theGame);
            var controller = new Exercise09Controller();
            var request = new System.Web.Routing.RequestContext(theContext, new System.Web.Routing.RouteData());
            controller.ControllerContext = new System.Web.Mvc.ControllerContext(request, controller);
            //Finally, set up the new guess
            var theGuess = new List<int>() { 2, 3, 4 };

            //Act
            controller.GuessTheDigits(theGuess);
            var result = controller.ShowPreviousGuesses();
            var lastGuess = ((List<Guess>)result.Model).LastOrDefault();    //Returns null if the list is empty

            //Assert
            /* NOTE : This line forces another implementation decision: to use a
             * C# property for Guess.Digits to represent the player's guess.
             * */
            CollectionAssert.AreEqual(theGuess, lastGuess.Digits);
        }

Controller:

using Prigmore2013_01.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace Prigmore2013_01.Tests
{
    public class Exercise09Controller : Controller
    {
        //
        // GET: /Exercise09/

        public ActionResult Index()
        {
            return View();
        }

        public ViewResult ShowPreviousGuesses()
        {

            var model = new List<Guess>();
            var m = new GuessingGame();



            if(HttpContext.Session["GameState"]  == null)
            {
                HttpContext.Session["GameState"] = new GuessingGame();
            }
            return View("Index", model);   


        }
        public ViewResult ShowGuessesMade()
        {
            return View();
        }

        public ActionResult GuessTheDigits(List<int> theGuess)
        {
            GuessingGame theGame = this.Session["GameState"] as GuessingGame;

            theGame.GuessTheHiddenDigits(theGuess);

            return RedirectToAction("Index");
        }


        public RedirectToRouteResult StartNewGame()
        {
            return RedirectToRoute(new
            {
                controller = "Index",
                action = "Index"
            });
        }
    }
}

Answer 1

Your issue is that you are creating a new instance of GuessingGame instead of altering the current this instance of it in your method:

Change this:

public void GuessTheHiddenDigits(List<int> list)
{
    GuessingGame playerGuess = new GuessingGame();
    playerGuess.Guesses = new List<int>();
    playerGuess.Guesses.AddRange(list);
}

Into this:

public void GuessTheHiddenDigits(List<int> list)
{
    this.Guesses = new List<int>();
    this.Guesses.AddRange(list);
}

Or more succinctly:

public void GuessTheHiddenDigits(IEnumerable<int> guesses)
{
    this.Guesses = new List<int>(guesses);
}

Answer 2

This might confuse you, but is this what you want?

public struct Guess
{
    public List<int> Digits { get; set; }
}
public class GuessingGame
{
    List<Guess> guesses;

    public GuessingGame()
    {
        guesses=new List<Guess>();
    }
    public void Guess(List<int> digits)
    {
        guesses.Add(new Guess() { Digits=digits });
    }
}

Answer 3

That would be

 playerGuess.Guesses.AddRange( list );