Cascading DropDown With AJAX

Step 1: Create a table in database

create table test

(

state1 varchar(50),

city varchar(50)

)

Step 2: In the .aspx Page

</select>

<asp:DropDownList ID="citylist" runat="server" Width="184px">

</asp:DropDownList>

Take statelist for State and citylist for City

When you select any item from statelist the citylist will automatically fill because of ajax

Step 3: Write this in the <head> Part

var xmlHttp

var arr;

function showCity() {

xmlHttp = GetXmlHttpObject()

var url = "Default.aspx"

url = url + "?name=" + document.getElementById('statelist').value

xmlHttp.onreadystatechange = stateChanged

xmlHttp.open("GET", url, true)

xmlHttp.send(null)

return false;

}

function stateChanged() {

if (xmlHttp.readyState == 4 || xmlHttp.readyState == "complete") {

var str;

str = xmlHttp.responseText;

arr = str.split(",");

var i;

for (i = 0; i < arr.length; i++) {

dd2 = document.getElementById("citylist")

var theOption = new Option;

theOption.text = arr[i];

theOption.value = arr[i];

dd2.options[i] = theOption;

}

function GetXmlHttpObject() {

var objXMLHttp = null

if (window.XMLHttpRequest) {

objXMLHttp = new XMLHttpRequest()

}

else if (window.ActiveXObject) {

objXMLHttp = new ActiveXObject("Microsoft.XMLHTTP")

}

return objXMLHttp

}

</script>

Step 4: In the .cs page

SqlConnection con = new SqlConnection("data source = MY\\SQLEXPRESS; initial catalog = try; integrated security=true");

protected void Page_Load(object sender, EventArgs e)

{

if (!Page.IsPostBack)

{

con.Open();

SqlCommand cmd = new SqlCommand("select * from test", con);

SqlDataReader dr;

dr = cmd.ExecuteReader();

statelist.DataSource = dr;

statelist.DataTextField = "state";

statelist.DataBind();

dr.Close();

con.Close();

}

if (Request.QueryString["name"] != null)

{

string name = Request.QueryString["name"];

Response.Clear();

con.Open();

SqlCommand cmd = new SqlCommand("select * from test where state=@state", con);

cmd.Parameters.AddWithValue("@state", name);

SqlDataReader dr;

dr = cmd.ExecuteReader();

string str = "";

int a = 0;

while (dr.Read())

{

if (a == 0)

str += dr["city"].ToString();

else

str += "," + dr["city"].ToString();

a++;

}

Response.Write(str);

Response.End();

con.Close();

}