Question

Ok so I have a checkbox list with n checkboxes. Everytime I check a box I want that number to get added to a list (Chosen). When the box is unchecked I want to remove it from the list. Then when I hit a button I want to display the list in a textbox. Here is my code:

public partial class _Default : System.Web.UI.Page
{
    List<int> Chosen = new List<int>();

    protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["Chosen"] == null)
        {
            Session["Chosen"] = new List<int>();
        } 

        Chosen = (List<int>)Session["Chosen"];

        for (int i = 0; i < Numbers.Items.Count; i++)
        {
            if (Numbers.Items[i].Selected) { Chosen.Add(i + 1); }
            else { Chosen.Remove(i + 1); }
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        foreach (var i in Chosen)
        {
            TextBox1.Text = Chosen[i].ToString();
        }
    }
}

Needless to say it does not work the way I want it to. When I select 1 and hit the button it writes 1 into the box, but if I unselect it and hit the button it leaves 1 there. Also if I select any number other than 1 I get an error on this line:

TextBox1.Text = Chosen[i].ToString();

Saying index is out of range. Yet when I debug the numbers seem to be allocating to the list properly.

Answer 1

Is this what you need?

<asp:TextBox ID="textBox1" runat="server">
</asp:TextBox>
<asp:CheckBoxList ID="Numbers" runat="server" 
                   OnSelectedIndexChanged="UpdateCheckBoxex" AutoPostBack="true">
    <asp:ListItem Text="One" Value="One" />
    <asp:ListItem Text="Two" Value="Two" />
    <asp:ListItem Text="Three" Value="Three" />
    <asp:ListItem Text="Four" Value="Four" />
</asp:CheckBoxList>


protected void UpdateCheckBoxex(object sender, EventArgs e)
{
    string s = string.Empty;
    new List<ListItem>(Numbers.Items.Cast<ListItem>().Where(i => i.Selected)).ForEach(x => s += string.Format("{0}, ", x.Text));
    textBox1.Text = s;        
}

In this case you don’t need Chosen, but if you still need to populate it, you dont need foreach loop

List<int> Chosen = new List<int>();
Chosen.AddRange(Numbers.Items.Cast<ListItem>().Where(i => i.Selected).Select(x => Numbers.Items.IndexOf(x) + 1));