Drop down list not updated when data changed

Question

I have a drop down list of categories that is databound. The selection from this populates a gridview. When I delete a category, it is successfully updating my gridview of products (showing no entries), but not he dropdownlist of categories until I re-run the program.

My page load:

protected void Page_Load(object sender, EventArgs e)
    {
        // Check if loaded for first time.
        if (!IsPostBack)
        {
            // Bind the data displayed in the Dropdownlists.
            Login.SelectAllCat(DropListCat);

        }
    }

My code to delete a category:

protected void BtnDeleteCat_Click(object sender, EventArgs e)
    {
        try
        {
            // Get int id from selectioin in drop down list.
            int id = Convert.ToInt32(DropListCat.SelectedValue.ToString());
            // Call method to open data base, create command from stored procedure and delete item to database.
            Login.DeleteCategory(id);
            // Update the data displayed in the Dropdownlists.
            Login.SelectAllCat(DropListCat);


        }
        catch (NullReferenceException)
        {
            LblProdId.Text = "No Category Selected!";
        }
    }

My dropdownlist:

<asp:DropDownList ID="DropListCat" runat="server" BackColor="#66FFFF"
            Width="200px" AutoPostBack="True" AppendDataBoundItems="True">
</asp:DropDownList>

My connection and binding code. In Login class .

// Method to select all categories and display them in dropdown lists.
public static void SelectAllCat(DropDownList list)
{
    // SqlConnection.
    SqlConnection con = new SqlConnection(conString);
    // Create new command and parameterise.
    SqlCommand cmd = new SqlCommand();
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.CommandText = "SelectAllCat";
    //
    // Adapted from
    // Source link: http://www.c-sharpcorner.com/UploadFile/abhikumarvatsa/data-binding-to-dropdownlist-and-listbox-in-Asp-Net/
    //
    cmd.Connection = con;
    try
    {
        // Open connection and bind data to GUI.
        con.Open();

        list.DataSource = cmd.ExecuteReader();
        list.DataTextField = "CatName";
        list.DataValueField = "CatID";
        list.DataBind();

    }
    catch (Exception ex)
    {
        throw ex;
    }
    finally
    {
        con.Close();
        con.Dispose();
    }
}

My stored procedure:

CREATE PROCEDURE SelectAllProd
AS
    SELECT * FROM Prod;
GO

This is the result after I have attempted to delete a category.
When I re-run the project, the category will have been deleted.

Edit

Actually, it is deleting the category, but it's retaining the original data binding from page load. So I guess I need to work out how to wipe that.

Answer 1

Write

    DropListCat.DataBind(); 

in BtnDeleteCat_Click

Answer 2

I fixed it by clearing the drop down list items before re-binding the data, as so:

// Method to select all categories and display them in dropdown lists.
    public static void SelectAllCat(DropDownList list)
    {
        // Clear any previously bound items.
        list.Items.Clear(); 
        // etc.../