private void SaveForm_Click(object sender, RoutedEventArgs e)
        {
            // input to an Customer object
            CustomerEntry customerEntry = new CustomerEntry();
            customerEntry.Id = CustomerRepository.Count() + 1;
            customerEntry.FirstName = FirstNameInput.Text;
            customerEntry.LastName = LastNameInput.Text;
            customerEntry.Telephone = PhoneInput.Text;
            customerEntry.Email = EmailInput.Text;

            // integer variable to pass Party Size integer in the if condition
            int partySize;
            // validate if an int was entered into the Party Size field
            // if not an integer was filled in...
            if (!int.TryParse(PartySizeInput.Text, out partySize))
            {
                //...then show error message...
                MessageBox.Show("Please enter a number for Party Size");
                //...and break out of the if statement
                return;
            }
            // otherwise parsed int is passed into the object customerEntry.PartySize
            customerEntry.PartySize = partySize;

            // Add above entry to grid
            CustomerRepository.Add(customerEntry);
            // Close current window
            Close();
        }
 private void customerDataGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
 {
     currentlySelectedCustomer = (CustomerEntry)customerDataGrid.SelectedItem;
 }