Pass and Retrieve the values of listbox in C#.net Windows Application

I want to insert multiple selected values into database in listbox.

I am using Windows application in C#.net.

I tried following code but did not work.

string ProductIDList;
SqlCommand com = new SqlCommand("Select ProductID from Product_Category where CategoryID=" + Catid +"" , con);
            dr = com.ExecuteReader();

            if (dr.HasRows)
            {
                while (dr.Read())


                    if (ProductIDList == "")
                    {
                        ProductIDList = dr["ProductID"].ToString();
                    }
                    else
                    {
                        ProductIDList = ProductIDList + "," + dr["ProductID"].ToString();
                    }

                ProductIDList = ProductIDList.Substring(1, ProductIDList.Length - 1开发者_StackOverflow社区);

            }
            dr.Close();

            var temparry = ProductIDList.Split(new string[] { "," }, StringSplitOptions.None);

          foreach (ListItem li in listBox1.Items)
            {

                foreach (string s in temparry)
                {
                    if (li.Value == s)
                        li.Selected = true;
                }
            }

In this code Foreach section ListItem not working in Windows application. I've done this thing before in asp.net application , But how can I do in Desktop(Windows) application?

Please help.

for (int i = 0; i < listBox1.Items.Count ; i++)
{
if (listbox1.Items[i].ToString() == s)
btw, I would also look at some refactoring. Arent there too many loops going on there?