practice/practiceApplicaiton/ClientEditPage.xaml.cs

namespace practiceApplicaiton;

public partial class ClientEditPage : ContentPage
{
    private readonly Client? _client;
    private List<TourFirm> _firms = [];

    public ClientEditPage(Client? client)
    {
        InitializeComponent();
        _client = client;
        Title = client == null ? "Новый клиент" : "Редактировать клиента";
    }

    protected override async void OnAppearing()
    {
        base.OnAppearing();
        _firms = await Repository.GetFirmsAsync();
        FirmPicker.ItemsSource = _firms.Select(f => f.FirmName).ToList();

        if (_client != null)
        {
            LastNameEntry.Text   = _client.LastName;
            FirstNameEntry.Text  = _client.FirstName;
            PatronymicEntry.Text = _client.Patronymic;
            PhoneEntry.Text      = _client.PhoneNumber;
            FirmPicker.SelectedIndex = _firms.FindIndex(f => f.FirmId == _client.FirmId);
        }
    }

    private async void OnSaveClicked(object sender, EventArgs e)
    {
        if (string.IsNullOrWhiteSpace(LastNameEntry.Text) ||
            string.IsNullOrWhiteSpace(FirstNameEntry.Text) ||
            string.IsNullOrWhiteSpace(PhoneEntry.Text) ||
            FirmPicker.SelectedIndex < 0)
        {
            await DisplayAlert("Ошибка", "Заполните все обязательные поля", "OK");
            return;
        }
        var c = new Client
        {
            ClientId    = _client?.ClientId ?? 0,
            FirmId      = _firms[FirmPicker.SelectedIndex].FirmId,
            LastName    = LastNameEntry.Text.Trim(),
            FirstName   = FirstNameEntry.Text.Trim(),
            Patronymic  = PatronymicEntry.Text?.Trim() ?? "",
            PhoneNumber = PhoneEntry.Text.Trim(),
        };
        try
        {
            if (_client == null) await Repository.AddClientAsync(c);
            else                 await Repository.UpdateClientAsync(c);
            await Navigation.PopAsync();
        }
        catch (Exception ex) { await DisplayAlert("Ошибка", ex.Message, "OK"); }
    }
}