AJAX Combo box

[copypaste]

my problem is that i have two combo box in asp.net .
one combo box has keep information about country .
second combo box has keep information about city .
both combo box has populated from database .
when i select any country from country combo box the second combo box (city

) has populatd from database without refreshing the page through AJAX.


please give the solution .

thanks

[kitwest]

Here's my best guess at a solution.
1. Include the following general-purpose script. (It could be maintained as a separate file and included as follows:
<script src="declareAndSendXmlHttpRequest.js"></script>)

var _req // XmlHttpRequest

function sendReq(page, qry, handler)
{
if (window.XMLHttpRequest)
{
_req = new XMLHttpRequest()
}
else if (window.ActiveXObject)
{
_req = new ActiveXObject("Microsoft.XMLHTTP")
}
else
{
alert ("Browser does not support HTTP Request.")
return
}
_req.onReadyStateChange = handler
var url = page + "?q=" + str
_req.open("GET", url, true)
_req.send(null)
}
2. In the combo box for Country, include the following:
onChange="countryChanged(this.value)"

In the city combo box, include the following:
<option>Please select a country first.</option>

3. Add a javascript function to handle when the country is selected:

function countryChanged(country)
{
sendReq('myPage.aspx', country, 'cityListReturned')
}

4. In your server page, include capability to look up the list of cities based on the Country returned in the query string, e.g. ?q=UK. The returned text should be in the html format to fill the city combo box, e.g.
<option>London</option>
<option>Birmingham</option>
<option>Liverpool</option>

4a. Since the list of cities should be relatively static, you might want to save trips to the database by maintaining a self-populating object in the Application:

Private Shared _cityList As DataTable
Public Shared Function CityList(ByVal country As String) As String
If _cityList Is Nothing Then
Dim ds As DataSet = QueryForCompleteListOfCitiesAndCountries()
_cityList = ds.Tables(0)
End If
Dim htmlList As String = ""
Dim dv As New DataView(_cityList)
dv.Filter = "country='" & country & "'"
dv.Sort = "city"
For c = 0 To dv.Items.Count - 1
htmlList &= "<option>" & dv.Items(c)("city").ToString & "</option>" & vbCrLf
Next
Return htmlList
End Function

5. Add a javascript function to handle when the request returns the list of cities:

function cityListReturned
{
if (_req.readyState == 4 || _req.readyState == "complete")
{
document.getElementById("city").innerHTML = _req.responseText
}
}

(Caution: I've never done this -- just having fun trying to guess how to solve it.)
Good luck!

[copypaste]

your code is not working