Remote Scripting in ASP.NET

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

namespace JSRS
{
	public class Cars : System.Web.UI.Page
	{
		protected System.Web.UI.WebControls.DropDownList ddlMake;
		protected System.Web.UI.WebControls.DropDownList ddlModel;
		protected System.Web.UI.WebControls.DropDownList ddlType;
		protected System.Web.UI.WebControls.Button btnCheck;
		protected System.Web.UI.WebControls.Label lblMake;
		protected System.Web.UI.WebControls.Label lblModel;
		protected System.Web.UI.WebControls.Label lblType;

		private DataSet ds
		{
			get
			{
				if (Session["ds"] != null)
					return (DataSet)Session["ds"];
				else
				{
					ds = new DataSet();
					ds.ReadXml(MapPath("Cars.xml"));
					Session["ds"] = ds;
					return ds;
				}
			}
			set { Session["ds"] = value; }
		}

		private void Page_Load(object sender, System.EventArgs e)
		{
			if (AMS.Web.RemoteScripting.InvokeMethod(this))
				return;

			ddlMake.Attributes.Add("onchange","LoadModel()");
			ddlModel.Attributes.Add("onchange","LoadType()");

			if (!Page.IsPostBack) 
			{
				ddlMake.DataSource = ds.Tables["Make"];
				ddlMake.DataTextField = "MakeName";
				ddlMake.DataValueField = "MakeID";
				ddlMake.DataBind();
				ddlMake.Items.Insert(0,new ListItem("","-1"));
			}

			ddlModel.DataSource = new DataView(ds.Tables["Model"], "MakeID='" + ddlMake.SelectedValue + "'", null, DataViewRowState.CurrentRows);
			ddlModel.DataTextField = "ModelName";
			ddlModel.DataValueField = "ModelID";
			ddlModel.DataBind();
			ddlModel.Items.Insert(0, new ListItem("","-1"));
			ddlModel.SelectedValue = Request["ddlModel"];

			ddlType.DataSource = new DataView(ds.Tables["Type"], "ModelID='" + ddlModel.SelectedValue + "'", null, DataViewRowState.CurrentRows);
			ddlType.DataTextField = "TypeName";
			ddlType.DataValueField = "TypeID";
			ddlType.DataBind();
			ddlType.Items.Insert(0, new ListItem("","-1"));
			ddlType.SelectedValue = Request["ddlType"];

		}

		#region Vom Web Form-Designer generierter Code
		override protected void OnInit(EventArgs e)
		{
			InitializeComponent();
			base.OnInit(e);
		}
		
		private void InitializeComponent()
		{    
			this.btnCheck.Click += new System.EventHandler(this.btnCheck_Click);
			this.Load += new System.EventHandler(this.Page_Load);

		}
		#endregion

		private void btnCheck_Click(object sender, System.EventArgs e)
		{
			lblMake.Text = "Make ID: "+ddlMake.SelectedItem;
			lblModel.Text = "Model ID: "+ddlModel.SelectedItem;
			lblType.Text = "Type ID: "+ddlType.SelectedItem;
		}

		public string GetModel(string MakeID) 
		{
			string output = "<option value='-1'></option>";
			foreach (DataRow row in ds.Tables["Model"].Select("MakeID='" + MakeID + "'"))
				output += "<option value='" + row[0] + "'>" + row[2] + "</option>";
			return output;

		}

		public string GetType(string ModelID) 
		{
			string output = "<option value='-1'></option>";
			foreach (DataRow row in ds.Tables["Type"].Select("ModelID='" + ModelID + "'"))
				output += "<option value='" + row[0] + "'>" + row[2] + "</option>";
			return output;
		}
	}
}