MyAvaloniaDemo/AuroraDesk.Presentation/Views/Pages/UdpClientPageView.axaml.cs

using System;
using System.Collections.Specialized;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using Avalonia.Controls;
using Avalonia.Markup.Xaml;
using AuroraDesk.Presentation.ViewModels.Pages;
using ReactiveUI;
using ReactiveUI.Avalonia;

namespace AuroraDesk.Presentation.Views.Pages;

public partial class UdpClientPageView : ReactiveUserControl<UdpClientPageViewModel>
{
    private ListBox? _receivedMessagesListBox;

    public UdpClientPageView()
    {
        InitializeComponent();

        this.WhenActivated(disposables =>
        {
            _receivedMessagesListBox ??= this.FindControl<ListBox>("ReceivedMessagesListBox");

            if (_receivedMessagesListBox is null)
            {
                return;
            }

            _receivedMessagesListBox.SelectedIndex = -1;

            IDisposable? messagesSubscription = null;
            IDisposable? autoScrollSubscription = null;

            var viewModelSubscription = this.WhenAnyValue(x => x.ViewModel)
                .Subscribe(vm =>
                {
                    messagesSubscription?.Dispose();
                    autoScrollSubscription?.Dispose();

                    if (vm is null)
                    {
                        return;
                    }

                    var currentVm = vm;
                    NotifyCollectionChangedEventHandler handler = (_, __) =>
                    {
                        if (currentVm.IsAutoScrollToBottom)
                        {
                            ScrollToBottom();
                        }
                    };

                    currentVm.ReceivedMessages.CollectionChanged += handler;
                    messagesSubscription = Disposable.Create(() =>
                    {
                        currentVm.ReceivedMessages.CollectionChanged -= handler;
                    });

                    autoScrollSubscription = currentVm.WhenAnyValue(x => x.IsAutoScrollToBottom)
                        .Subscribe(isEnabled =>
                        {
                            if (isEnabled)
                            {
                                ScrollToBottom();
                            }
                        });

                    if (currentVm.IsAutoScrollToBottom)
                    {
                        ScrollToBottom();
                    }
                })
                ;
            disposables.Add(viewModelSubscription);

            disposables.Add(Disposable.Create(() =>
            {
                messagesSubscription?.Dispose();
                autoScrollSubscription?.Dispose();
            }));
        });
    }

    private void InitializeComponent()
    {
        AvaloniaXamlLoader.Load(this);
    }

    private void ScrollToBottom()
    {
        if (_receivedMessagesListBox is null)
        {
            return;
        }

        var messages = ViewModel?.ReceivedMessages;

        if (messages is null || messages.Count == 0)
        {
            return;
        }

        var lastItem = messages[messages.Count - 1];
        _receivedMessagesListBox.ScrollIntoView(lastItem);
        _receivedMessagesListBox.SelectedIndex = -1;
    }
}