display countries,states,cities Using Combo Box.

hi firstly check for the event of state combobox it must be firing an event.
if if it firing an event then you can write your code in that event as follows

private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection("provide connection string here");
DataSet ds = new DataSet();
SqlDataAdapter da=new SqlDataAdapter("select " + state + " from " + country, conn);
da.Fill(ds);
ds.Tables[0]; this will have one column which has all the data of cities for the state and country you've selected
}
when you are done with this you can bind this ds.tables[0] with your comboBox.
Note:- state and country here are string variables,and they are selected values of respective dropdowns
Mark your answer as solved if you've got the answer
thanks.

This earlier question[^] may help you.

<ComboBox Grid.Column="8" Grid.Row="8" Height="23" HorizontalAlignment="Left" Name="comboBox2" VerticalAlignment="Center" Width="180">
                <ComboBoxItem Content="Days" />
                <ComboBoxItem Content="Weeks" />
                <ComboBoxItem Content="Months" />
                <ComboBoxItem Content="Years" />
            </ComboBox>

simple example

make 2 tables
first for countries
like this
CountryId CountryName
1 Palestine
2 Germany
3 .......

the second for states
CountryId StateId StateName CiteisName
1 1 Jerusalem abo dees-selawan-shoafat-bait hanena-...
1 2 Gazza gazza-khan yones-rafah-der albalh-...
1 3 Tulkarm Illar-Attil-alnazleh-....
*********************************************************************************
1- first fill the ComboCountries (by code or insert it manualy)
2- when you choose any contry search in the states table like this :
select StateName form states where CountryId = " & CountryId & " oeder by StateName
and fill the combo of states with result
3- when you choose any State search in the states table like this
select CiteisName form states where StateName = '" & compo3 & "' oeder by StateName
4-
CompoCiteis.clear
Dim CityArry() As String
CityArry() = Split(rs.Fields(0), "-")
For i = 0 To UBound(CityArry)
CompoCiteis.additem CityArry(i)
Next

i hope this help

Now run the applicationusing System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;

namespace CountryStateCity
{
public partialclass WebForm1 : System.Web.UI.Page
{
private SqlConnection conn = new SqlConnection("Data source=.; uid=sa; pwd=Password$2; database=CountryStateCity");

public void Bind_ddlCountry()
{
conn.Open();
SqlCommand cmd =new SqlCommand("select County,CountryId from Country", conn);
SqlDataReader dr = cmd.ExecuteReader();
ddlcountry.DataSource = dr;
ddlcountry.Items.Clear();
ddlcountry.Items.Add("--Please Select country--");
ddlcountry.DataTextField = "County";
ddlcountry.DataValueField = "CountryId";
ddlcountry.DataBind();
conn.Close();
}
public void Bind_ddlState()
{
conn.Open();

SqlCommand cmd =new SqlCommand("select State,StateID from countryState where CountryId='" + ddlcountry.SelectedValue +"'", conn);

SqlDataReader dr = cmd.ExecuteReader();
ddlstate.DataSource = dr;
ddlstate.Items.Clear();
ddlstate.Items.Add("--Please Select state--");
ddlstate.DataTextField = "State";
ddlstate.DataValueField = "StateID";
ddlstate.DataBind();
conn.Close();
}
public void Bind_ddlCity()
{
conn.Open();
SqlCommand cmd =new SqlCommand("select * from stateCity where StateId ='" + ddlstate.SelectedValue +"'", conn);

SqlDataReader dr = cmd.ExecuteReader();
ddlcity.DataSource = dr;
ddlcity.Items.Clear();
ddlcity.Items.Add("--Please Select city--");
ddlcity.DataTextField = "City";
ddlcity.DataValueField = "CityID";
ddlcity.DataBind();
conn.Close();
}
protectedvoid Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
Bind_ddlCountry();
}
}
protectedvoid ddlcountry_SelectedIndexChanged(object sender, EventArgs e)
{
Bind_ddlState();
}
protectedvoid ddlstate_SelectedIndexChanged(object sender, EventArgs e)
{
Bind_ddlCity();
}
}
}
Now run the application