Question : populating combobox asynchronasly

can any one tell me how u can populate 2nd combobox using first combobox selection in Silverlight3 but i need it asynchronasly like ajax.please give me code example
Thanks

Answer : populating combobox asynchronasly

In the code below, I have a list of states and once the user selects a state, all the cities of the state appear in the second combo box.

// xaml code:

   
       
       
   
   
       
       
   
   
                 SelectionChanged="StateComboBox_SelectionChanged" Width="75" />
                 Width="150" />
                  Text="Loading Cities..." FontSize="15" />


// code-behind
public partial class MainPage : UserControl
{
   // add Service Reference:
   // http://www.webservicex.net/uszip.asmx
   // to the SL project
   public MainPage()
   {
       InitializeComponent();
       Loaded += MainPage_Loaded;
   }

   void MainPage_Loaded(object sender, RoutedEventArgs e)
   {
       MessageBlock.Visibility = Visibility.Collapsed;
       StateComboBox.Items.Add("AZ");
       StateComboBox.Items.Add("CA");
       StateComboBox.Items.Add("FL");
       StateComboBox.Items.Add("HI");
   }

   private void StateComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
   {
       MessageBlock.Visibility = Visibility.Visible;
       CityComboBox.Items.Clear();
       USZipSoapClient zipSoapClient = new USZipSoapClient();
       zipSoapClient.GetInfoByStateCompleted += ZipSoapClient_GetInfoByStateCompleted;
       string stateCode = StateComboBox.SelectedItem.ToString();
       zipSoapClient.GetInfoByStateAsync(stateCode);
   }

   void ZipSoapClient_GetInfoByStateCompleted(object sender, GetInfoByStateCompletedEventArgs e)
   {
       string xmlResult = e.Result.ToString();
       XmlReader resultXml = XmlReader.Create(new StringReader(xmlResult));
       while (resultXml.Read())
       {
           if (resultXml.NodeType != XmlNodeType.Element) continue;
           switch (resultXml.LocalName.ToLower())
           {
               case "city":
                   string cityName = resultXml.ReadInnerXml();
                   if(!CityComboBox.Items.Contains(cityName))
                   {
                       CityComboBox.Items.Add(cityName);
                   }
                   break;
           }
       }
       MessageBlock.Visibility = Visibility.Collapsed;
   }
}