Bind A DropDownList With Another DropDownList In ASP.NET Web Forms

 <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="BindingDropDownList.WebForm1" %>


<!DOCTYPE html>


<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

    <title></title>

    <style type="text/css">

        .auto-style1{

            width:100%;

        }

        .auto-style2 {

            width: 64px;

        }

    </style>

</head>

<body>

    <form id="form1" runat="server">

        <div>

            <table cellpadding="4" cellspacing="4" class="auto-style1">

                <tr>

                    <td class="auto-style2">Country</td>

                    <td>

                        <asp:DropDownList ID="CountryDropDownList" runat="server" Width="177px" OnSelectedIndexChanged="CountryDropDownList_SelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>

                        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="CountryDropDownList" Display="Dynamic" SetFocusOnError="true" ErrorMessage="Country is required" ForeColor="Red" InitialValue="Select Country"></asp:RequiredFieldValidator>

                    </td>

                </tr>

                <tr>

                    <td class="auto-style2">City</td>

                    <td>

                        <asp:DropDownList ID="CityDropDownList" runat="server" Width="177px"></asp:DropDownList>

                        <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="CityDropDownList" Display="Dynamic" SetFocusOnError="true" ErrorMessage="City is required" ForeColor="Red" InitialValue="Select City"></asp:RequiredFieldValidator>

                    </td>

                </tr>

                <tr>

                    <td class="auto-style2"></td>

                    <td>

                        <asp:Button ID="SubmitButton" runat="server" Text="Submit" OnClick="SubmitButton_Click"/>

                    </td>

                </tr>

            </table>

        </div>

    </form>

</body>

</html>

ABOVE FILE IS WebForm1.aspx
















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;
using System.Configuration;

namespace BindingDropDownList
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        string cs = ConfigurationManager.ConnectionStrings["dbcs"].ConnectionString;
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindCountryDDL();
            }
        }

        void BindCountryDDL()
        {
            try
            {
                using (SqlConnection con = new SqlConnection(cs))
                {
                    con.Open();
                    string query = "SELECT * FROM country";
                    SqlDataAdapter sda = new SqlDataAdapter(query,con);
                    DataTable data = new DataTable();
                    sda.Fill(data);
                    CountryDropDownList.DataSource = data;
                    CountryDropDownList.DataTextField = "country_name";
                    CountryDropDownList.DataValueField = "country_id";
                    CountryDropDownList.DataBind();

                    ListItem selectItem = new ListItem("Select Country", "Select Country");
                    selectItem.Selected = true;
                    CountryDropDownList.Items.Insert(0, selectItem);
                }
            }
            catch (SqlException ex)
            {
                Response.Write("SqlException: " + ex.Message);
            }
            catch (Exception ex)
            {
                Response.Write("Exception: " + ex.Message);
            }
        }

        void BindCityDDL(int country_id)
        {
            try
            {
                using (SqlConnection con = new SqlConnection(cs))
                {
                    string query = "SELECT * FROM city WHERE c_id=@country_id";
                    SqlDataAdapter sda = new SqlDataAdapter(query,con);
                    sda.SelectCommand.Parameters.AddWithValue("@country_id",country_id);
                    DataTable data = new DataTable();
                    sda.Fill(data);
                    CityDropDownList.DataSource = data;
                    CityDropDownList.DataTextField = "city_name";
                    CityDropDownList.DataValueField = "city_id";
                    CityDropDownList.DataBind();

                    ListItem selectItem = new ListItem("Select City","Select City");
                    selectItem.Selected = true;
                    CityDropDownList.Items.Insert(0,selectItem);
                }
            }
            catch (SqlException ex)
            {
                Response.Write("SqlException: " + ex.Message);
            }
            catch (Exception ex)
            {
                Response.Write("Exception: " + ex.Message);
            }
        }

        protected void CountryDropDownList_SelectedIndexChanged(object sender, EventArgs e)
        {
            try
            {
                int country_id = Convert.ToInt32(CountryDropDownList.SelectedValue);
                BindCityDDL(country_id);
            }
            catch (SqlException ex)
            {
                Response.Write("<script>alert('Country is Required')</script>");
            }
            catch (Exception ex)
            {
                Response.Write("<script>alert('Country is Required Field')</script>");
            }
        }

        protected void SubmitButton_Click(object sender, EventArgs e)
        {
            Response.Write("Selected Country is : " + CountryDropDownList.SelectedItem.ToString() + "<br>");
            Response.Write("Selected Country ID is : " + CountryDropDownList.SelectedValue.ToString() + "<br>");

            Response.Write("Selected City is : " + CityDropDownList.SelectedItem.ToString() + "<br>");
            Response.Write("Selected City ID is : " + CityDropDownList.SelectedValue.ToString() + "<br>");
        }
    }
}
ABOVE FILE IS WebForm1.aspx.cs


















<?xml version="1.0" encoding="utf-8"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  https://go.microsoft.com/fwlink/?LinkId=169433
  -->
<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.7.2" />
    <httpRuntime targetFramework="4.7.2" />
    <pages>
      <namespaces>
        <add namespace="System.Web.Optimization" />
      </namespaces>
      <controls>
        <add assembly="Microsoft.AspNet.Web.Optimization.WebForms" namespace="Microsoft.AspNet.Web.Optimization.WebForms" tagPrefix="webopt" />
      </controls>
    </pages>
  </system.web>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="Antlr3.Runtime" publicKeyToken="eb42632606e9261f" />
        <bindingRedirect oldVersion="0.0.0.0-3.5.0.2" newVersion="3.5.0.2" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.Web.Infrastructure" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="0.0.0.0-2.0.0.0" newVersion="2.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" />
        <bindingRedirect oldVersion="0.0.0.0-13.0.0.0" newVersion="13.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="WebGrease" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="0.0.0.0-1.6.5135.21930" newVersion="1.6.5135.21930" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
  <system.codedom>
    <compilers>
      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701" />
      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" />
    </compilers>
  </system.codedom>
<connectionStrings>
<add name="dbcs" connectionString="Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=D:\DotNet\BindingDropDownList\BindingDropDownList\App_Data\CountryCityDB.mdf;Integrated Security=True" providerName="System.Data.SqlClient"/>
</connectionStrings>
<appSettings>
<add key="ValidationSettings:UnobtrusiveValidationMode" value="None"/>
</appSettings>
</configuration>
ABOVE FILE IS Web.config
















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