using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

namespace WebApplication3
{
    public partial class _Default : System.Web.UI.Page
    {   
        public class car
        {
            private string color;
            private int chelun = 4;

            public string Color
            {
                get
                {
                    return color;
                }
                set
                {
                    color = value;
                }
            }
            public int Chelun
            {
                get
                {
                    return chelun;
                }
            }
            public string Getinfo(string a, string  b)
            {
                string c = "";
                switch (a)
                {
                    case "#red":
                        c +="#你的车子是红颜色的,共有" + b + "轮子!";
                        break;
                    case "#black":
                        c += "你的车子是黑颜色的,共有" + b + "轮子!";
                        break;
                    case "#white":
                        c += "你的车子是白颜色的,共有" + b + "轮子!";
                        break;
                }
                return c;
            }
        }
        protected void Page_Load(object sender, EventArgs e)
        {
        }

        protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            car NewCar = new car();

            NewCar.Color = DropDownList1.SelectedValue.ToString();
            string bb = NewCar.Color.ToString();
            string  cc = NewCar.Chelun.ToString();

            string dd = NewCar.Getinfo(bb, cc);
            Response.Write(dd);
        }
    }
}



目的是:当点击下拉表的时,显示上面的车颜色的提示...
我找了好长时间,也没找出来,请高手指点!

像你这样那个颜色的属性不没有，把下拉框的点击事件改变颜色的属性，再给他写一个方法这个方法就说你这句话，这样就会清楚一点，

注意,要把DropDownList1的属性AutoPostBack设置为true
一下是代码:

using System;

public partial class _Default : System.Web.UI.Page 
{
    public enum color { 黑色, 红色, 白色 }

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            this.DropDownList1.Items.Add(color.黑色.ToString());
            this.DropDownList1.Items.Add(color.白色.ToString());
            this.DropDownList1.Items.Add(color.红色.ToString());
        }
        this.DropDownList1.SelectedIndexChanged += new EventHandler(DropDownList1_SelectedIndexChanged);
    }

    void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string choose = this.DropDownList1.SelectedItem.Text;
        car c = new car();
        switch (choose)
        {
            case "黑色": c.carColor = color.黑色; break;
            case "白色": c.carColor = color.白色; break;
            case "红色": c.carColor = color.红色; break;
        }
        this.Label1.Text = c.getCarInfo();
    }

    public class car
    {
        public color carColor { get; set; }
        public int cartwheel { get { return 4; } }

        public string getCarInfo()
        {
            return "你选择的是" + carColor.ToString() + "的轿车,它有" + this.cartwheel + "个轮子!";
        }
    }
}

楼上的代码写的真不错,学习!