private void newIndividualBtn_Click(object sender, RoutedEventArgs e) { UserSingleton user = UserSingleton.Instance; DataHandlingSingleton export = DataHandlingSingleton.Instance; int result = 0; // Input Validation. Standard UK phone number length is 11 digits bool validation = int.TryParse(phoneNumberTxt.Text, out result); if (phoneNumberTxt.Text.Length == 11 && validation == false) { user.NewUser(phoneNumberTxt.Text); // Output data to CSV export.GenerateCSVUser(user.CurrentUser); } else { // Display error message MessageBox.Show("Invalid UK Phone Number. Try again."); } // Adding User IDs to all user combo boxes, unless they already exist foreach (UserSingleton aUser in user.Users) { if (!userList.Items.Contains(aUser.UserId)) { userList.Items.Add(aUser.UserId); individualList1.Items.Add(aUser.UserId); individualList2.Items.Add(aUser.UserId); } } // Reset text field phoneNumberTxt.Text = ""; }