Invalid attempt to call Read when reader is closed

Question

I'm running a DbDataReader on a query to remove items from a dropdownlist if they are already attached to a specific submission, and I keep getting an error telling me the reader is closed. Can't see why my reader is being seen as closed here. What am I missing?

 protected void Page_Load(object sender, EventArgs e)
{

    string x = Request.QueryString["SubId"];
    string connectionString = System.Configuration.ConfigurationManager.
        ConnectionStrings["MyConnectionString"].ConnectionString;
    string displayQuery = "SELECT CustName, CustAdd, CustCity, CustState, " +
        "CustZip FROM Customer WHERE SubId =" + x;
    string broQuery = "SELECT EntityType FROM Broker WHERE SubId =" + x;
    string ddlQuery = "SELECT ProductId FROM SubmissionProducts " +
        "WHERE SubmissionId =" + x;
    using (SqlConnection displayConn = new SqlConnection(connectionString))
    {
        displayConn.Open();
        SqlCommand DlistCmd = new SqlCommand(ddlQuery, displayConn);

        using (SqlDataReader Ddldr = DlistCmd.ExecuteReader())
        {
            while (Ddldr.Read())
            {

                switch (Ddldr.GetInt32(0))
                {
                    case 1:
                        DdlProductList.Items.RemoveAt(1);
                        break;
                    case 2:
                        DdlProductList.Items.RemoveAt(2);
                        break;
                    case 3:
                        DdlProductList.Items.RemoveAt(3);
                        break;
                    case 4:
                        DdlProductList.Items.RemoveAt(4);
                        break;
                    case 5:
                        DdlProductList.Items.RemoveAt(5);
                        break;
                    case 6:
                        DdlProductList.Items.RemoveAt(6);
                        break;
                    case 7:
                        DdlProductList.Items.RemoveAt(7);
                        break;
                    default:
                        break;
                }
                Ddldr.Close();
            }

        }

Answer 1

Remove this line:

Ddldr.Close();

Answer 2

Don't call Ddldr.Close();, especially inside the while. This way you are doing a first iteration, closing the reader and the second iteration will of course booom as the reader is closed. The using statement will take care of it. Simply remove this line from your code.

So:

using (SqlDataReader Ddldr = DlistCmd.ExecuteReader())
{
    while (Ddldr.Read())
    {
        switch (Ddldr.GetInt32(0))
        {
            ... your cases here
            default:
                break;
        }
    }
}

Also the following lines:

string x = Request.QueryString["SubId"];
string displayQuery = "SELECT CustName, CustAdd, CustCity, CustState, CustZip FROM Customer WHERE SubId =" + x;
string broQuery = "SELECT EntityType FROM Broker WHERE SubId =" + x;
string ddlQuery = "SELECT ProductId FROM SubmissionProducts WHERE SubmissionId =" + x;

stink like a pile of s..t. You should be using parametrized queries and absolutely never write any code like this or your application will be vulnerable to SQL injection. Everytime you use a string concatenation when writing a SQL query an alarm should ring telling you that you are doing it wrong.

So here comes the correct way of doing this:

protected void Page_Load(object sender, EventArgs e)
{
    string x = Request.QueryString["SubId"];
    string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
    using (var conn = new SqlConnection(connectionString))
    using (var cmd = conn.CreateCommand())
    {
        conn.Open();
        cmd.CommandText = "SELECT ProductId FROM SubmissionProducts WHERE SubmissionId = @SubmissionId";
        cmd.Parameters.AddWithValue("@SubmissionId", x)

        using (var reader = cmd.ExecuteReader())
        {
            while (Ddldr.Read())
            {
                switch (reader.GetInt32(reader.GetOrdinal("ProductId")))
                {
                    ... your cases here
                    default:
                        break;
                }
            }

        }
    }
}