ASP.Net C＃和Microsoft SQL连接

我的项目在asp.net的webform1中，包括一个文本框和一个保存按钮，当用户在文本框中输入某个国家/地区名称时，应单击“保存”按钮，该名称应保存在名为country的数据库表中。然后在webform2中，保存的国家/地区应在页面加载时加载到dropdownlist中，然后应该有一些文本框，用户将在其中输入下拉列表中所选国家/地区的状态，在最后一个webform3国家中，当用户选择一个国家/地区时，它会在dropdownlist中加载在另一个下拉列表中加载该国家的州，并且当用户从第二个下拉列表中选择一个州并输入该州的城市时，应通过单击保存按钮将其保存在数据库中。我在运行webform2时遇到问题，将国家/地区加载到下拉列表1中，但是当我选择一个国家/地区时，它不会在dropdownlist2中加载该国家/地区的状态。有什么帮助吗？到目前为止，这是我的代码，

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;

namespace assign1 {
    public partial class city: System.Web.UI.Page {
        protected void Page_Load(object sender, EventArgs e) {
            if (IsPostBack == false) {
                SqlConnection conn = new SqlConnection("Data Source = HAFIZ_HARRON; Database = 7thSemester; Integrated Security = true");
                SqlDataAdapter da = new SqlDataAdapter();
                da.SelectCommand = new SqlCommand("SELECT CName,CID FROM country", conn);

                DataTable dt = new DataTable();
                da.Fill(dt);

                ddlCountry.DataSource = dt;
                ddlCountry.DataTextField = "CName";
                ddlCountry.DataValueField = "CID";
                ddlCountry.DataBind();
            }


        }

        protected void btnSave_Click(object sender, EventArgs e) {
            SqlConnection conn = new SqlConnection("Data Source = HAFIZ_HARRON; Database = 7thSemester; Integrated Security = true");

            SqlCommand cmd = new SqlCommand("INSERT INTO city(CIName,SID,CID) Values('" + txtCity.Text + "','" + ddlState.SelectedIndex + "','" + ddlCountry.SelectedIndex + "')", conn);




            conn.Open();
            cmd.ExecuteNonQuery();
            conn.Close();

        }

        protected void ddlState_SelectedIndexChanged(object sender, EventArgs e) {
            /* SqlConnection conn = new SqlConnection("Data Source = HAFIZ_HARRON; Database = 7thSemester; Integrated Security = true");
            SqlDataAdapter da = new SqlDataAdapter();
            da.SelectCommand = new SqlCommand("SELECT SName,SID FROM state", conn);

            DataTable dt = new DataTable();
            da.Fill(dt);

            ddlState.DataSource = dt;
            ddlState.DataTextField = "SName";
            ddlState.DataValueField = "SID";
            ddlState.DataBind(); */

        }

        protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e) {
            SqlConnection conn = new SqlConnection("Data Source = HAFIZ_HARRON; Database = 7thSemester; Integrated Security = true");
            SqlDataAdapter da = new SqlDataAdapter();
            da.SelectCommand = new SqlCommand("SELECT SName,SID FROM state", conn);

            DataTable dt = new DataTable();
            da.Fill(dt);

            ddlState.DataSource = dt;
            ddlState.DataTextField = "SName";
            ddlState.DataValueField = "SID";
            ddlState.DataBind();
        }
    }
}


----------