How do I keep data in a generic list after postback

Question

I am trying to populate a Nested Repeater by databinding it to a Generic List.

The user will be able to add / remove values from this Generic List at will.
All this is neatly wrapped in an Ajax Update Panel.

I am now having a problem that when the user tries to add values to the Generic List, it only adds ` initial value, then keeps updating that value when they click to add more.

I have a suspicion that its because the Generic List doesn't keel its initial data or something; but I'm really not too sure.

Please can someone help.

Chalenge.cs

public class challenge
{
    public class Team
    {
        public string TeamName { get; set; } 
    }
    public class Member:Team
    {
        public string Name { get; set; }
    }

    //This is just a test, but I cant get a list in a class file to work properly.
    public class ChallengeList
    {
        public List<Member> Member()
        {
            return null;
        }
    }
}

Page.cs

private List<challenge.Member> Members = new List<challenge.Member>();

protected void Page_Load(object sender, EventArgs e)
{
    if (Page.IsPostBack) return;

    lblCurrent.Text = SiteSession.Current.Nickname;
    lblChallenge.Text = Request.QueryString["Challenge"];

    //Add the initial teams
    PopulateTeamRepeater();
    AddData();
}

private List<challenge.Member> AddData()
{
    Members.Add(
        new challenge.Member
            {
                Name = SiteSession.Current.Nickname,
                TeamName = "Team One"
            });
    Members.Add(
            new challenge.Member
                {
                    Name = Request.QueryString["Challenge"],
                    TeamName = "Team Two"
                });

    return Members;
}

/// <summary>
/// Add the selected member to the team
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void drpTeams_SelectedIndexChanged(object sender, EventArgs e)
{
    Members.Add(
        new challenge.Member
        {
            Name = tbMemberAuto.Text,
            TeamName = drpTeams.SelectedItem.Value
        });


    PopulateTeamRepeater();
}

UPDATE: Binding of the repeaters (Same page)

 /// <summary>
    /// Populates the Team repeater control with the amount of teams the user has selected
    /// </summary>
    private void PopulateTeamRepeater()
    {


        ArrayList cArrayList = new ArrayList(); //Main holder
        StringBuilder sb = new StringBuilder(); //Temp holer

        try
        {

            //Get all team numbers
            foreach (challenge.Member Team in AddData())
            {
                //Add it to the string builder
                sb.Append(Team.TeamName + ";");
            }

            //Split the string to get the strings (As a temporary holder)
            string[] cs = sb.ToString().Split(';');

            //Add the groups (unique) to the next holder
            foreach (string s in cs.Where(s => !cArrayList.Contains(s)))
            {
                cArrayList.Add(s);
            }

            rptTeam.DataSource = cArrayList;
            rptTeam.DataBind();
        }
        catch (Exception es)
        {
            misc.ChangeInfo(Master.Page, "Error filling teams: " + es.Message, "ui-state-error");
        }
    }

/// <summary>
/// Populate the Member repeater based on the Team
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void rptTeam_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
    Repeater rptMembers = (Repeater)e.Item.FindControl("rptMembers");
    Label lblTeam = (Label)e.Item.FindControl("lblTeam");

    rptMembers.DataSource = AddData().Where(m => m.TeamName == lblTeam.Text);
    rptMembers.DataBind();
}

Answer 1

You can keep them on view state as:

const string cChalMemNameConst = "ChalMem_cnst";

public List<challenge.Member> Members
{
    get
    {
        if (!(ViewState[cChalMemNameConst] is List<challenge.Member>))
        {
            // need to fix the memory and added to viewstate
            ViewState[cChalMemNameConst] = new List<challenge.Member>();
        }

        return (List<challenge.Member>)ViewState[cChalMemNameConst];
    }
}

Also add the [Serializable] attributes on your class that you place on the List<> as:

[Serializable]
public class challenge
{
    [Serializable]
    public class Team
    {
        public string TeamName { get; set; } 
    }

    [Serializable]
    public class Member:Team
    {
        public string Name { get; set; }
    }

    [Serializable]
    public class ChallengeList
    {
        public List<Member> Member()
        {
            return null;
        }
    }
}

note: The line private List<challenge.Member> Members = new List<challenge.Member>(); must be change by the above statement of save it to viewstate.