How to get data in one combo at the SelectionChanged event of other combo in Silverlight

My application is in Silverlight(c#.Net)

I have a form with three combo boxes,Country,State,City.

My requirement is I want to populate my State Combo box at the Selectionchanged Event of Country combo box.

When the user select some country than the State of that Country should be populated in State combo.

Database Tables:

• Country Table-(CountryID,CountryName)
• State Table-(StateID,StateName,CountryId)
• City Table-(CityID,CityName,StateId)

To retrieve value from Database im coding in Service.svc.cs File

This is my Code. This code will get Country Record.

    public class GetCountry
            {
                public string CountryName { get; set; }
            }

     [OperationContract]
            public List<GetCountry> GetCountryRecord()
            {
                using (Entities context = new Entities())
                {
                    return (from c in context.CountryMasters
                            select new GetCountry
                       开发者_C百科     {
                                CountryName = c.CountryName,
                            }).ToList<GetCountry>();
                }
            }

  //Code to Get State from State_Master table


  public class GetState
    {
        public string StateName { get; set; }
    }



   [OperationContract]
    public List<GetState> GetStateRecord(int countryId)
    {
        using (Entities context = new Entities())
        {
            return (from c in context.StateMasters
                    select new GetState 
                    {
                        StateName = c.StateName,
                    }).ToList<GetState>();
        }
    }
   //End of State Code

This is my code in Form.xaml.cs. It will populate countries in Country combo box

     client = new ServiceReference1.AlumniServiceClient();
      client.GetCountryRecordCompleted += (s, ea) =>
                    {
                        cboCountry.ItemsSource = ea.Result.Select(b => b.CountryName).ToList();
                    };
                client.GetCountryRecordAsync();

Please Suggest me Changes in the query in my Service.svc.cs file to get my required result or any other way to get it.

    return (**from c in context.StateMasters
                            select new GetState**  

This is my code in Form.xaml.cs at selectionChanged Event of Country Combobox

    private void cboCountry_SelectionChanged(object sender, SelectionChangedEventArgs e)
            {
                var client = new ServiceReference1.AlumniServiceClient();

                client.GetStateRecordCompleted += (s, ea) =>
                {
                    cboState.ItemsSource = ea.Result.Select(b => b.StateName).ToList();                     };
                client.GetStateRecordAsync();
            }

But this will get me All the States present in the StatesMaster

This might not answer your direct question but I believe its a better solution to what you are trying to achieve
Let your Country data construct on the client side have a property of ObservableCollection<State>, then bind the State ComboBox's ItemsSource to the SelectedItem.States of the Countries ComboBox (using ElementName binding), then you don't need to worry about SelectionChanged events etc. The same will apply to State & City relationship.
As a non-US citizen I feel obliged to remind you that most other Countries do not have 'States' :)

This might not answer your direct question but I believe its a better solution to what you are trying to achieve Let your Country data construct on the client side have a property of ObservableCollection<State>, then bind the State ComboBox's ItemsSource to the SelectedItem.States of the Countries ComboBox (using ElementName binding), then you don't need to worry about SelectionChanged events etc. The same will apply to State & City relationship. As a non-US citizen I feel obliged to remind you that most other Countries do not have 'States' :)