webform 下拉列表联动

ublic partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DropDown();
        }
       
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string userName = TextBox1.Text;
        string userPass = TextBox2.Text;        
        //HttpCookie cookie = Request.Cookies["userName"];
        ////string value = cookie.Value;
        //if (cookie.Value == user)
        //{
        //    HttpCookie cookie2 = Request.Cookies["userPass"];
        //    TextBox2.Text = cookie2.Value;
        //}
        bool user = new UserdBF().Select(userName, userPass);
        if (user)
        {
            if (CheckBox1.Checked)
            {
                HttpCookie cookie1 = new HttpCookie("userName", userName);
                cookie1.Expires = DateTime.Now.AddHours(2);
                Response.SetCookie(cookie1);
                HttpCookie cookie2 = new HttpCookie("userPass", userPass);
                cookie2.Expires = DateTime.Now.AddHours(2);
                Response.SetCookie(cookie1);
            }
            Response.Write("<script>alert('登录成功');</script>");
        }
        else
        {
            Response.Write("<script>alert('用户名或密码错误');</script>");
        }
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        Response.Redirect("Default2.aspx");
    }
    public void DropDown()
    {
        List<AreaFull> list = new AreaBF().Select(0);
        DropDownList1.DataSource = list;
        DropDownList1.DataTextField = "AreaName";
        DropDownList1.DataValueField = "AreaId";
        DropDownList1.DataBind();
        int a = Convert.ToInt32(DropDownList1.SelectedItem.Value);
        List<AreaFull> listS = new AreaBF().Select(a);
        DropDownList2.DataSource = listS;
        DropDownList2.DataTextField = "AreaName";
        DropDownList2.DataValueField = "AreaId";
        DropDownList2.DataBind();
        int b = Convert.ToInt32(DropDownList2.SelectedItem.Value);
        List<AreaFull> listQ = new AreaBF().Select(b);
        DropDownList3.DataSource = listQ;
        DropDownList3.DataTextField = "AreaName";
        DropDownList3.DataValueField = "AreaId";
        DropDownList3.DataBind();
        TextBox3.Text = DropDownList1.SelectedItem.Text + DropDownList2.SelectedItem.Text + DropDownList3.SelectedItem.Text;
       
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        int a = Convert.ToInt32(DropDownList1.SelectedItem.Value);
        List<AreaFull> listS = new AreaBF().Select(a);
        DropDownList2.DataSource = listS;
        DropDownList2.DataTextField = "AreaName";
        DropDownList2.DataValueField = "AreaId";
        DropDownList2.DataBind();
        int b = Convert.ToInt32(DropDownList2.SelectedItem.Value);
        List<AreaFull> listQ = new AreaBF().Select(b);
        DropDownList3.DataSource = listQ;
        DropDownList3.DataTextField = "AreaName";
        DropDownList3.DataValueField = "AreaId";
        DropDownList3.DataBind();
        TextBox3.Text = DropDownList1.SelectedItem.Text + DropDownList2.SelectedItem.Text + DropDownList3.SelectedItem.Text;
    }
    protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
    {
        int b = Convert.ToInt32(DropDownList2.SelectedItem.Value);
        List<AreaFull> listQ = new AreaBF().Select(b);
        DropDownList3.DataSource = listQ;
        DropDownList3.DataTextField = "AreaName";
        DropDownList3.DataValueField = "AreaId";
        DropDownList3.DataBind();
        TextBox3.Text = DropDownList1.SelectedItem.Text + DropDownList2.SelectedItem.Text + DropDownList3.SelectedItem.Text;
    }
    protected void DropDownList3_SelectedIndexChanged(object sender, EventArgs e)
    {
        TextBox3.Text = DropDownList1.SelectedItem.Text + DropDownList2.SelectedItem.Text + DropDownList3.SelectedItem.Text;
    }
}