Приложение MVVM. Быстрая "Нестрогая MVVM" реализация

        private string? inputText;
        private object selectedManufacturer = ViewsHelper.AllManufacturers;
        public string? SearchText
        {
            get => inputText;
            set { inputText = value; SearchChanged(); }
        }
        public object SearchManufacturer
        {
            get => selectedManufacturer;
            set { selectedManufacturer = value ?? ViewsHelper.AllManufacturers; SearchChanged(); }
        }
 
        private FilterEventHandler? filter;
        private void SearchChanged()
        {
            string searchText = inputText?.Trim() ?? string.Empty;
            Manufacturer? searchManufacturer = selectedManufacturer as Manufacturer;
            source.Filter -= filter;
 
            filter = (string.IsNullOrEmpty(searchText), searchManufacturer == null) switch
            {
                (false, false) => NameManufacturerSearch,
                (false, true) => NameSearch,
                (true, false) => ManufacturerSearch,
                _ => null,
            };
 
            source.Filter += filter;
 
            void NameSearch(object sender, FilterEventArgs e)
            {
                e.Accepted = ((Product)e.Item).Name.Contains(searchText);
            }
            void ManufacturerSearch(object sender, FilterEventArgs e)
            {
                e.Accepted = ((Product)e.Item).Manufacturer == searchManufacturer;
            }
            void NameManufacturerSearch(object sender, FilterEventArgs e)
            {
                Product product = (Product)e.Item;
                e.Accepted = product.Manufacturer == searchManufacturer &&
                             product.Name.Contains(searchText);
            }
        }

        private string? inputText;
        private object selectedManufacturer = ViewsHelper.AllManufacturers;
        public string? SearchText
        {
            get => inputText;
            set { inputText = value; SearchChanged(); }
        }
        public object SearchManufacturer
        {
            get => selectedManufacturer;
            set { selectedManufacturer = value ?? ViewsHelper.AllManufacturers; SearchChanged(); }
        }
 
        private FilterEventHandler? filter;
        private void SearchChanged()
        {
            string searchText = inputText?.Trim() ?? string.Empty;
            Manufacturer? searchManufacturer = selectedManufacturer as Manufacturer;
            source.Filter -= filter;
 
            filter = (string.IsNullOrEmpty(searchText), searchManufacturer == null) switch
            {
                (false, false) => (object sender, FilterEventArgs e) =>
                {
                    Product product = (Product)e.Item;
                    e.Accepted = product.Manufacturer == searchManufacturer &&
                                 product.Name.Contains(searchText);
                }
                ,
                (false, true) => (object sender, FilterEventArgs e) => e.Accepted = ((Product)e.Item).Name.Contains(searchText),
                (true, false) => (object sender, FilterEventArgs e) => e.Accepted = ((Product)e.Item).Manufacturer == searchManufacturer,
                _ => null,
            };
 
            source.Filter += filter;
        }