级联下拉列表在使用c＃的asp.net中不起作用。（不使用ajax） [英] Cascading dropdownlist does not work in asp.net using c#.(not using ajax)

问题描述

<asp:DropDownList ID="countrylist" runat="server" 

                    onselectedindexchanged="countrylist_SelectedIndexChanged" AutoPostBack="True">
               </asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td class="style5">
                    state</td>
                <td class="style6">
                            
                    <asp:DropDownList ID="statelist" runat="server"  

                        onselectedindexchanged="statelist_SelectedIndexChanged" AutoPostBack="True">
                    </asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td class="style2">
                    City</td>
                <td>
                            
                    <asp:DropDownList ID="city" runat="server" 

                        onselectedindexchanged="city_SelectedIndexChanged" AutoPostBack="True">
                    </asp:DropDownList>

namespace tables
{
    public partial class CompanyRegi : System.Web.UI.Page
    {
       protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
               
                Contrydropdown();
 
                
            }
        }
 

        protected void Contrydropdown()
        {
            //conenction path for database
            SqlConnection con = new SqlConnection("Data Source=jayraj-pc\\sqlexpress;Initial Catalog=Internship;Integrated Security=True;Pooling=False");
            con.Open();
            SqlCommand cmd = new SqlCommand("select * from Country", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
 

 
            countrylist.DataSource = ds;
            countrylist.DataTextField = "CountryName";
            countrylist.DataValueField = "CountryID";
            countrylist.DataBind();
            countrylist.Items.Insert(0, new ListItem("--Select--", "0"));
            statelist.Items.Insert(0, new ListItem("--Select--", "0"));
            city.Items.Insert(0, new ListItem("--Select--", "0"));
            con.Close();
 

        }
        /// Bind State Dropdown Based on CountryID

        protected void countrylist_SelectedIndexChanged(object sender, EventArgs e)
        {
            int CountryID = Convert.ToInt32(countrylist.SelectedValue);
            SqlConnection con = new SqlConnection("Data Source=jayraj-pc\\sqlexpress;Initial Catalog=Internship;Integrated Security=True;Pooling=False");
            con.Open();
            SqlCommand cmd = new SqlCommand("select * from State where CountryID=" + CountryID, con);
 
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
 

 
            statelist.DataSource = ds;
            statelist.DataTextField = "StateName";
            statelist.DataValueField = "StateID";
            statelist.DataBind();
            statelist.Items.Insert(0, new ListItem("--Select--", "0"));
            con.Close();
 
            if (statelist.SelectedValue == "0")
            {
                city.Items.Clear();
                city.Items.Insert(0, new ListItem("--Select--", "0"));
            }
 
        }
 
        protected void statelist_SelectedIndexChanged(object sender, EventArgs e)
        {
            int StateID = Convert.ToInt32(statelist.SelectedValue);
            SqlConnection con = new SqlConnection("Data Source=jayraj-pc\\sqlexpress;Initial Catalog=Internship;Integrated Security=True;Pooling=False");
            con.Open();
            SqlCommand cmd = new SqlCommand("select * from City where StateID=" + StateID, con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
            con.Close();
            city.DataSource = ds;
            city.DataTextField = "CityName";
            city.DataValueField = "CityID";
            city.DataBind();
            city.Items.Insert(0, new ListItem("--Select--", "0"));
        }
 
        protected void city_SelectedIndexChanged(object sender, EventArgs e)
        {
 
        }

推荐答案

这里是更新面板替代例示

Here's the update panel alternative examplified

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="SampleCascade.aspx.cs" Inherits="Lunch.SampleCascade" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:ScriptManager runat="server" ID="AjaxScriptManager" EnablePartialRendering="True"></asp:ScriptManager>
    <div>
        <asp:UpdatePanel runat="server" ID="UpdPnl" UpdateMode="Always">
            <ContentTemplate>
                <div>
                    <label>Country</label>
                    <asp:DropDownList runat="server" ID="CountryDropDown" AutoPostBack="True" OnSelectedIndexChanged="CountryDropDownSelectedIndexChanged">
                    <asp:ListItem Value="dk" Selected="True">Denmark</asp:ListItem>
                    <asp:ListItem Value="ca">Canada</asp:ListItem>
                </asp:DropDownList>
                </div>
                <div>
                    <label>City</label>
                    <asp:DropDownList runat="server" ID="CityDropDown" AutoPostBack="True" OnSelectedIndexChanged="CityDropDownSelectedIndexChanged">
                    </asp:DropDownList>
                </div>
                <asp:Label runat="server" ID="Feedback"></asp:Label>
            </ContentTemplate>
        </asp:UpdatePanel>

    </div>
    </form>
</body>
</html>

并且代码背后

and with code behind

using System;
using System.Collections.Generic;
using System.Web.UI.WebControls;

namespace Lunch
{
    public partial class SampleCascade : System.Web.UI.Page
    {
        private Dictionary<string, HashSet<string>> _cities = new Dictionary<string, HashSet<string>>();

        protected void Page_Init(object sender, EventArgs e)
        {
            _cities.Add("dk", new HashSet<string>(new []{ "Copenhagen", "Aalborg", "Odense" }));
            _cities.Add("ca", new HashSet<string>(new [] { "Ottawa", "Toronto", "Charlottetown" }));
        }

        protected void Page_Load(object sender, EventArgs e)
        {
            if(!IsPostBack)
                LoadCities(CountryDropDown.SelectedValue);
        }

        protected void CountryDropDownSelectedIndexChanged(object sender, EventArgs e)
        {
            var ctry = (DropDownList) sender;
            LoadCities(ctry.Items[ctry.SelectedIndex].Value);
            Feedback.Text = "Loaded cities for " + ctry.Items[ctry.SelectedIndex].Text;
        }

        protected void CityDropDownSelectedIndexChanged(object sender, EventArgs e)
        {
            var city = (DropDownList) sender;
            ListItem selected = city.Items[city.SelectedIndex];
            if (selected.Value == "0") return;
            Feedback.Text = "City selected: " + selected.Text;
        }

        private void LoadCities(string country)
        {
            CityDropDown.Items.Clear();
            foreach (var itm in _cities[country])
            {
                CityDropDown.Items.Add(new ListItem(itm, itm.ToLower()));
            }
            CityDropDown.Items.Insert(0, new ListItem("Select", "0"));
        }


    }
}

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