Clienty/Clienty/MainWindow.axaml.cs

using Avalonia.Controls;
using Clienty.Models;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Clienty
{
    public partial class MainWindow : Window
    {
        List<Client> filteredClientList = new List<Client>();
        public MainWindow()
        {
            InitializeComponent();
            Listbox.ItemsSource = Helper.ClientList;

            // Список для ComboBox "Пол"
            List<string> polList = new List<string>
            {
                "По умолчанию",
                "мужчины",
                "женщины"
            };
            FiltrPoPolu.ItemsSource = polList;

            // Список для ComboBox "Отсортировать по"
            List<string> sortList = new List<string>
            {
                "в алфавитном порядке",
                "по дате регистрации"
            };
            FiltVsyakoe.ItemsSource = sortList;
        }


        private void TextBox_TextChanged(object? sender, Avalonia.Controls.TextChangedEventArgs e)
        {
            Change();
        }

        private void ComboBox_SelectionChanged(object? sender, Avalonia.Controls.SelectionChangedEventArgs e)
        {
            Change();
        }

        private void ComboBox_SelectionChanged_1(object? sender, Avalonia.Controls.SelectionChangedEventArgs e)
        {
            Change();
        }

        public void Change()
        {
            try
            {
                filteredClientList = Helper.ClientList;
                // search
                if (!string.IsNullOrEmpty(SearchClient.Text) || !string.IsNullOrWhiteSpace(SearchClient.Text))
                {
                    var searchText = SearchClient.Text.ToLower().Trim();
                    filteredClientList = string.IsNullOrWhiteSpace(searchText)
                    ? Helper.ClientList.ToList() // Если нет текста, показываем всех клиентов
                    : Helper.ClientList.Where(c =>
                        c.Firstname.ToLower().Contains(searchText) ||
                        c.Lastname.ToLower().Contains(searchText) ||
                        (c.Patronymic != null && c.Patronymic.ToLower().Contains(searchText)) ||
                        (c.Email != null && c.Email.ToLower().Contains(searchText)) ||
                        c.Phone.Contains(searchText)
                    ).ToList();

                }

                // sort
                switch (FiltVsyakoe.SelectedIndex)
                {
                    case 0:
                        filteredClientList = filteredClientList.OrderBy(c => c.Lastname).ToList();
                        break;
                    case 1:
                        filteredClientList = filteredClientList.OrderBy(c => c.Registrationdate).ToList();
                        break;

                }

                // filter
                if (FiltrPoPolu.SelectedIndex > 0)
                {
                    var selectedGender = FiltrPoPolu.SelectedIndex > 0 && FiltrPoPolu.SelectedItem.ToString() == "мужчины" ? 1 : 2;
                    filteredClientList = filteredClientList.Where(c => c.Gendercode == selectedGender.ToString().ToCharArray()[0]).ToList();
                }
                Listbox.ItemsSource = filteredClientList;


            }
            catch
            {
                return;
            }
            //Kolich.Text = 
        }

        private async void Button_Click(object? sender, Avalonia.Interactivity.RoutedEventArgs e)
        {
            await new AddEdit().ShowDialog(this);
            Change();
        }

        private async void Border_DoubleTapped(object? sender, Avalonia.Input.TappedEventArgs e)
        {
            //var clientId = int.Parse(((sender as Border).Tag as string));
            //await new AddEdit(clientId).ShowDialog(this);
            //Change();
        }
    }
}