private void Form4_Load(object sender, EventArgs e) { List <City> city = new List <City>(); city = CountryDB.GetAllCities(); foreach (City r in city) { comboBox1.Items.Add(new ComboBoxItem(r.Name, Convert.ToString(r.ID))); } List <Country> country = new List <Country>(); country = CountryDB.GetAllCountries(); foreach (Country r in country) { comboBox2.Items.Add(new ComboBoxItem(r.Name, r.Code)); } }