DropDown Dynamic loadDate

[hans]

I had a question about the Dropdown element, I saw how to search for it, but I couldn't find it for dynamic
    public SearchWarehouseNP()
    {
        InitializeComponent();
        dropdownSettlement.DropDownStyle = RadDropDownStyle.DropDown;
        dropdownSettlement.AutoCompleteMode = AutoCompleteMode.Suggest;

        dropdownSettlement.DropDownListElement.AutoCompleteSuggest = new CustomAutoCompleteSuggestHelperUpdate(
            dropdownSettlement.DropDownListElement,
            async query =>
            {
                if (string.IsNullOrWhiteSpace(query) || query.Length < 3)
                    return Enumerable.Empty<DescriptionTextListDataItem>();

                var response = await _searchSettlementService.GetCityData(query);
                if (response.success && response.data.Any())
                {
                    return response.data.First().Addresses.Select(a => new DescriptionTextListDataItem
                    {
                        Text = $"{a.MainDescription} ({a.Area})",
                        Value = a.MainDescription,
                        DescriptionText = a.Area
                    });
                }

                return Enumerable.Empty<DescriptionTextListDataItem>();
            }
        );

        dropdownSettlement.SelectedIndexChanged += (s, e) =>
        {
            if (dropdownSettlement.SelectedItem is DescriptionTextListDataItem selectedItem)
            {
                Console.WriteLine($"Выбрано: {selectedItem.Text} ({selectedItem.Value})");
            }
        };
    }
}
The problem is that the data is not stored in Items

Console.WriteLine empty

using Telerik.WinControls.UI;

namespace NovaPostOrderManager.Helpers;

public class CustomAutoCompleteSuggestHelperUpdate : AutoCompleteSuggestHelper
{
    private readonly Func<string, Task<IEnumerable<DescriptionTextListDataItem>>> _fetchDataAsync;
    private CancellationTokenSource _cts = new();

    public CustomAutoCompleteSuggestHelperUpdate(RadDropDownListElement owner, Func<string, Task<IEnumerable<DescriptionTextListDataItem>>> fetchDataAsync)
        : base(owner)
    {
        _fetchDataAsync = fetchDataAsync;
    }

    protected override async void SyncItemsCore()
    {
        // Текущий текст из поля ввода
        string currentInput = Filter;

        // Проверяем, нужно ли загружать данные
        if (string.IsNullOrWhiteSpace(currentInput) || currentInput.Length < 3)
        {
            DropDownList.ListElement.Items.Clear();
            DropDownList.ClosePopup();
            return;
        }

        // Отменяем предыдущий запрос
        _cts.Cancel();
        _cts = new CancellationTokenSource();

        try
        {
            // Задержка перед началом запроса
            await Task.Delay(300, _cts.Token);

            // Загружаем данные
            var items = await _fetchDataAsync(currentInput);

            _cts.Token.ThrowIfCancellationRequested();

            DropDownList.ListElement.BeginUpdate();
            DropDownList.ListElement.Items.Clear();

            // Добавляем элементы в выпадающий список
            foreach (var item in items)
            {
                DropDownList.ListElement.Items.Add(item);
            }

            DropDownList.ListElement.EndUpdate();

            if (DropDownList.ListElement.Items.Count > 0)
            {
                DropDownList.ShowPopup(); // Показываем список, если есть элементы
            }
            else
            {
                DropDownList.ClosePopup();
            }
        }
        catch (TaskCanceledException)
        {
            // Запрос был отменён — игнорируем
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Ошибка загрузки данных: {ex.Message}");
        }
    }

    protected override bool DefaultFilter(RadListDataItem item)
    {
        if (item is not DescriptionTextListDataItem descriptionItem)
            return base.DefaultFilter(item);

        return descriptionItem.Text.Contains(Filter, StringComparison.CurrentCultureIgnoreCase) ||
               descriptionItem.DescriptionText.Contains(Filter, StringComparison.CurrentCultureIgnoreCase);
    }
}

[Dinko | Tech Support Engineer]

Hi hans,

I appreciate your interest in our RadDropDownList control for WinForms. I have checked the code but it's still unclear to me what is your requirement here. May I ask you to elaborate more on your question. If you can isolate your approach in a sample project with dummy data, that would be great. This way I can debug the code and try to find a suitable solution for your scenario.

I am looking forward to your reply.

Regards,
Dinko | Tech Support Engineer
Progress Telerik

[hans]

https://drive.google.com/drive/folders/1xSnBc-VEk-9Wa1UH9CZPlGIrVXTF-h0t?usp=sharing

[Dinko | Tech Support Engineer]

Thank you for the project, however, I will need some guidance to reproduce this behavior. May I ask you to send steps that I will follow and observe what is the current behavior and what you are trying to implement in your application? When I run the project, I see some logic form with empty dropdown lists.

[hans]

1) after starting the project there is a DropDownList very first
2) it needs to write "Київ" in Ukrainian
3) after that a problem arises, items are not loaded correctly and SeelctedItem is not selected
4) and from the second query Items is selected but it is empty

[hans]

are you having any success?

[Dinko | Tech Support Engineer]

The provided steps are greatly appreciated. Upon debugging this behavior, the Filter property in the CustomAutoCompleteSuggestHelper3.SyncItemsCore is executed too early. You can observe that if you type "Київ" and then add an empty space, the dropdown will pop up and the data. 

What you can do is move the logic in the ApplyFilterToDropDown() method. Here is the whole class:

public class CustomAutoCompleteSuggestHelper3 : AutoCompleteSuggestHelper
{
    private readonly Func<string, Task<IEnumerable<DescriptionTextListDataItem>>> _fetchDataAsync;

    public CustomAutoCompleteSuggestHelper3(RadDropDownListElement owner, Func<string, Task<IEnumerable<DescriptionTextListDataItem>>> fetchDataAsync)
        : base(owner)
    {
        _fetchDataAsync = fetchDataAsync;
    }

    public override async void ApplyFilterToDropDown(string filter)
    {
        base.ApplyFilterToDropDown(filter);

        string currentInput = Filter;
        if (string.IsNullOrWhiteSpace(currentInput) || currentInput.Length < 3)
        {
            DropDownList.ListElement.Items.Clear();
            DropDownList.ClosePopup();
            return;
        }

        try
        {
            // Получаем данные
            var items = await _fetchDataAsync(currentInput);

            DropDownList.ListElement.BeginUpdate();
            DropDownList.ListElement.Items.Clear();

            foreach (var item in items)
            {
                DropDownList.ListElement.Items.Add(item);
            }

            DropDownList.ListElement.EndUpdate();

            if (DropDownList.ListElement.Items.Count > 0)
            {
                DropDownList.ShowPopup(); // Показываем выпадающий список
            }
            else
            {
                DropDownList.ClosePopup();
            }
        }
        catch (TaskCanceledException)
        {
            // Игнорируем отменённые запросы
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Ошибка загрузки данных: {ex.Message}");
        }
    }

    protected override bool DefaultFilter(RadListDataItem item)
    {
        if (item is not DescriptionTextListDataItem descriptionItem)
            return base.DefaultFilter(item);

        return descriptionItem.Text.Contains(Filter, StringComparison.CurrentCultureIgnoreCase) ||
               descriptionItem.DescriptionText.Contains(Filter, StringComparison.CurrentCultureIgnoreCase);
    }
}

I hope that this approach will work in your project.