C＃中的ASP.Net复选框

Question

Ok so I am getting into programing in ASP.Net with C#. I am trying a very simple procedure but it is very buggy. So I have the following ASP code:

<asp:Button ID="Button1" runat="server" Text="Show Numbers" onclick="Button1_Click1" />
            <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            <asp:CheckBox ID="CheckBox1" runat="server" 
            oncheckedchanged="CheckBox1_CheckedChanged" />

I then have the following C# code behind it:

    int i = 0;
    List<int> Chosen = new List<int>();

    public void Page_Load(object sender, EventArgs e)
    {


    }
    public void Button1_Click1(object sender, EventArgs e)
    {
        if (i == 0)
        {
            TextBox1.Text = "Nothing here!";
        }
        else if (i == 1)
        {
            TextBox1.Text = Chosen[0].ToString();
        }
    }
    protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
    {
        if (CheckBox1.Checked == true)
        {
            Chosen.Add(1);
            i++;
            CheckBox1.Checked = true;
        }
        else if (CheckBox1.Checked == false)
        {
            Chosen.Remove(1);
            i--;
            CheckBox1.Checked = false;
        }
    }

The goal of the code is to have a checkbox on the screen. If it is checked I want to add the number 1 to my list (Chosen) also, when I push the button I want the textbox to display the number 1. If the checkbox becomes unchecked I want the number to get removed from the list and when I push the button I want it to display "Nothing here!".

The problem is, sometimes it works and sometimes it doesn't. For example if I click the box then the button it works. Then when I click the button again it says "Nothing Here!" it should stay as a 1.

Answer 1

You have to set AutoPostBack=true to the CheckBox control markup and also save that list into Session dictinary.

List<int> Chosen;

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