Object reference not set to an instance of an object

[MartinSmith]

I am trying to write a simple user control to hold a cached HTML "Select" Box

This works fine if I drag the control onto the page directly (in which case I can't work out how to access the control's properties) but errors if I try and programmatically load it into a placeholder


A cut down version of how I am trying to do this is below...

using ShoppingCart_Net.Controls;

namespace ShoppingCart_Net.productdb
{
	public class browser_home : System.Web.UI.Page
	{
		protected CachedListBox clbTypes = new CachedListBox();
	
		private void Page_Load(object sender, System.EventArgs e)
		{
			string ConnectionString = ConfigurationSettings.AppSettings["ConnectionString"].ToString();
			phTypes.Controls.Add(clbTypes);
			clbTypes.Query = "Select ProductTypes.ProductTypeID,ProductTypes.ProductTypeDescription From ProductTypes Order By ProductTypes.ProductTypeDescription";
			clbTypes.TextField = "ProductTypeDescription";
			clbTypes.ValueField = "ProductTypeID";
			clbTypes.ConnectionString = ConnectionString;
		}


	}
}

The CachedListBox.ascx page just contains one line (apart from the directives) as below.

<aspropDownList id="lbCached" runat="server"></aspropDownList>


The (cut down) code behind for the user control is...

namespace ShoppingCart_Net.Controls
{
	using System.Data.OleDb;

	public class CachedListBox : System.Web.UI.UserControl
	{
		protected System.Web.UI.WebControls.DropDownList lbCached;
		private string mQuery, mConnectionString, mTextField, mValueField;

		private void Page_Load(object sender, System.EventArgs e)
		{
			if (! this.IsPostBack) 
			{
				OleDbConnection objConn = new OleDbConnection(mConnectionString);
				OleDbCommand objComm = new OleDbCommand(mQuery, objConn);
				objConn.Open();
				try
				{
					lbCached.DataTextField = mTextField;
					lbCached.DataValueField = mValueField;
					lbCached.DataSource = objComm.ExecuteReader();
					lbCached.DataBind();
				}
				finally
				{
					objConn.Close();
				}
			}
		} 




		
		public string Query
		{
			get
			{
				return mQuery;
			}
			set
			{
				mQuery = value;
			}
		}

		
//Other Properties omitted for conciseness
	}
}

The Error occurs at the first use of lbCached in the Page_Load event above and is as follows...

"Exception Details: System.NullReferenceException: Object reference not set to an instance of an object."

Can anyone see what I am doing wrong?

Cheers!

Martin