public class CountriesViewModel : INotifyPropertyChanged
            {
                static String connectionString = @"connstr";
                SqlConnection con;
                SqlCommand cmd;
                SqlDataAdapter adapter;
                DataSet ds;
                public ObservableCollection<Country> Countries { get; set; }
                public String txtSelectedItem { get; set; }
                public CountriesViewModel()
                {
                    txtSelectedItem = "Please select a country";
                    FillList();
                }
        
                public void FillList()
                {
                    try
                    {
                        con = new SqlConnection(connectionString);
                        con.Open();
                        cmd = new SqlCommand("select * from [dbo].[Country]", con);
                        adapter = new SqlDataAdapter(cmd);
                        ds = new DataSet();
                        adapter.Fill(ds, "tblCountries");
        
                        if (Countries == null)
                            Countries = new ObservableCollection<Country>();
        
                        foreach (DataRow dr in ds.Tables[0].Rows)
                        {
                            Countries.Add(new Country
                            {
                                CountryId = Convert.ToInt32(dr[0].ToString()),
                                CountryName = dr[1].ToString(),
                               
                            });
                        }
                    }
                    catch (Exception ex)
                    {
        
                    }
                    finally
                    {
                        ds = null;
                        adapter.Dispose();
                        con.Close();
                        con.Dispose();
                    }
                }
                public event PropertyChangedEventHandler PropertyChanged;
        
                private void OnPropertyChanged(string propertyName)
                {
                    if (PropertyChanged != null)
                    {
                        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
                    }
                }
            }