Passing C# String as SQL parameter for SELECT WHERE IN

Question

I am writing a function to take as many multiple selected items from a Listbox and pass the vaules to a SQL Query to INSERT values into a table after selecting the filtered values from another table. The code I have typed is below and it doesn't seem to work (the problem is with the way I'm passing the string to the query.

string lbSites = "";

protected void Button1_Click1(object sender, EventArgs e)
{
    string cns = "server=abc;database=testDB;Trusted_Connection=True";
    using (SqlConnection con = new SqlConnection(cns))
    {
        using (SqlCommand command = con.CreateCommand())
        {
            command.CommandText = "INSERT INTO Activity (Hostname,Site,Status,System_Dept,Business_Dept)"
                + "SELECT * FROM Inventory WHERE Site IN ("+lbSites+");"
                ; 
            con.Open();
            command.Parameters.AddWithValue("@lbSites", lbSites);
            command.ExecuteNonQuery();
            con.Close();
        }
    }
}

protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (ListBox1.Items.Count > 0)
    {
        for (int i = 0; i < ListBox1.Items.Count; i++)
        {
            if (ListBox1.Items[i].Selected)
            {
                lbSites += "'" + ListBox1.Items[i].Value + "', ";
            }
        }
    }
}

Answer 1

The value of lbSites is lost everytime you've posted back. Keep it in your ViewState.

Besides, you don't need command.Parameters.AddWithValue("@lbSites", lbSites); since there's no @lbSites parameter in your sql.