In this article I will explain how to build Country State City Cascading DropDownList in ASP.Net i.e. Country State City Cascading DropDownList populated from Database and dependent on each other.
Database
For this example I have created a SQL Server database named Cascading_ddl, the script of which is attached along with the sample code.
In this database I have created tables for storing Country, State and City named as Countries, States and Cities respectively with schema shown below
Countries Table
States Table
Cities Table
Creating the Database
You will have to simply execute the script named CreateCascadingDatabase.sql stored in the SQL Folder of the attached sample and it will create the complete database with data.
HTML Markup
Below is the HTML Markup which contains three ASP.Net DropDownList controls each for Country, State and City. I have placed all the three DropDownLists inside ASP.Net UpdatePanel control to avoid full PostBack and make use of AJAX.
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<table>
<tr>
<td>Country:</td>
<td><asp:DropDownList ID="ddlCountries" runat="server" AutoPostBack = "true" OnSelectedIndexChanged = "Country_Changed">
</asp:DropDownList>
</td>
</tr>
<tr>
<td>State:</td>
<td>
<asp:DropDownList ID="ddlStates" runat="server" AutoPostBack = "true" OnSelectedIndexChanged = "State_Changed">
</asp:DropDownList>
</td>
</tr>
<tr>
<td>City:</td>
<td>
<asp:DropDownList ID="ddlCities" runat="server">
</asp:DropDownList>
</td>
</tr>
</table>
</ContentTemplate>
</asp:UpdatePanel>
Generic function to Bind and populate the ASP.Net DropDownList
Below is the generic function that will be used to populate and bind the ASP.Net DropDownList with data from the SQL Server Database
C#
private void BindDropDownList(DropDownList ddl, string query, string text, string value, string defaultText)
{
string conString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
SqlCommand cmd = new SqlCommand(query);
using (SqlConnection con = new SqlConnection(conString))
{
using (SqlDataAdapter sda = new SqlDataAdapter())
{
cmd.Connection = con;
con.Open();
ddl.DataSource = cmd.ExecuteReader();
ddl.DataTextField = text;
ddl.DataValueField = value;
ddl.DataBind();
con.Close();
}
}
ddl.Items.Insert(0, new ListItem(defaultText, "0"));
}
VB.Net
Private Sub BindDropDownList(ddl As DropDownList, query As String, text As String, value As String, defaultText As String)
Dim conString As String = ConfigurationManager.ConnectionStrings("ConString").ConnectionString
Dim cmd As New SqlCommand(query)
Using con As New SqlConnection(conString)
Using sda As New SqlDataAdapter()
cmd.Connection = con
con.Open()
ddl.DataSource = cmd.ExecuteReader()
ddl.DataTextField = text
ddl.DataValueField = value
ddl.DataBind()
con.Close()
End Using
End Using
ddl.Items.Insert(0, New ListItem(defaultText, "0"))
End Sub
Populating the Country DropDownList
The Country DropDownList is populated on Page_Load event of the page as shown below
C#
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
string query = "select CountryId, CountryName from Countries";
BindDropDownList(ddlCountries, query, "CountryName", "CountryId", "Select Country");
ddlStates.Enabled = false;
ddlCities.Enabled = false;
ddlStates.Items.Insert(0, new ListItem("Select State", "0"));
ddlCities.Items.Insert(0, new ListItem("Select City", "0"));
}
}
VB.Net
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
If Not IsPostBack Then
Dim query As String = "select CountryId, CountryName from Countries"
BindDropDownList(ddlCountries, query, "CountryName", "CountryId", "Select Country")
ddlStates.Enabled = False
ddlCities.Enabled = False
ddlStates.Items.Insert(0, New ListItem("Select State", "0"))
ddlCities.Items.Insert(0, New ListItem("Select City", "0"))
End If
End Sub
Populating the State DropDownList
The State DropDownList is populated on OnSelectedIndexChanged event of the Country DropDownList as shown below
C#
protected void Country_Changed(object sender, EventArgs e)
{
ddlStates.Enabled = false;
ddlCities.Enabled = false;
ddlStates.Items.Clear();
ddlCities.Items.Clear();
ddlStates.Items.Insert(0, new ListItem("Select State", "0"));
ddlCities.Items.Insert(0, new ListItem("Select City", "0"));
int countryId = int.Parse(ddlCountries.SelectedItem.Value);
if (countryId > 0)
{
string query = string.Format("select StateId, StateName from States where CountryId = {0}", countryId);
BindDropDownList(ddlStates, query, "StateName", "StateId", "Select State");
ddlStates.Enabled = true;
}
}
VB.Net
Protected Sub Country_Changed(sender As Object, e As EventArgs)
ddlStates.Enabled = False
ddlCities.Enabled = False
ddlStates.Items.Clear()
ddlCities.Items.Clear()
ddlStates.Items.Insert(0, New ListItem("Select State", "0"))
ddlCities.Items.Insert(0, New ListItem("Select City", "0"))
Dim countryId As Integer = Integer.Parse(ddlCountries.SelectedItem.Value)
If countryId > 0 Then
Dim query As String = String.Format("select StateId, StateName from States where CountryId = {0}", countryId)
BindDropDownList(ddlStates, query, "StateName", "StateId", "Select State")
ddlStates.Enabled = True
End If
End Sub
Populating the City DropDownList
The City DropDownList is populated on OnSelectedIndexChanged event of the State DropDownList as shown below
C#
protected void State_Changed(object sender, EventArgs e)
{
ddlCities.Enabled = false;
ddlCities.Items.Clear();
ddlCities.Items.Insert(0, new ListItem("Select City", "0"));
int stateId = int.Parse(ddlStates.SelectedItem.Value);
if (stateId > 0)
{
string query = string.Format("select CityId, CityName from Cities where StateId = {0}", stateId);
BindDropDownList(ddlCities, query, "CityName", "CityId", "Select City");
ddlCities.Enabled = true;
}
}
VB.Net
Protected Sub State_Changed(sender As Object, e As EventArgs)
ddlCities.Enabled = False
ddlCities.Items.Clear()
ddlCities.Items.Insert(0, New ListItem("Select City", "0"))
Dim stateId As Integer = Integer.Parse(ddlStates.SelectedItem.Value)
If stateId > 0 Then
Dim query As String = String.Format("select CityId, CityName from Cities where StateId = {0}", stateId)
BindDropDownList(ddlCities, query, "CityName", "CityId", "Select City")
ddlCities.Enabled = True
End If
End Sub
Demo
Downloads
You can download the complete source code in VB.Net and C# along with the script to create the database, tables and their contents using the download link provided below
