kev/Drawer/AI/Views/MainWindow.axaml.cs

using Avalonia.Controls;
using Avalonia.Interactivity;
using Avalonia.Platform.Storage;
using Avalonia.Threading;
using AI.ViewModels;

namespace AI.Views
{
    public partial class MainWindow : Window
    {
        private bool _isUserAtBottom = true; // 跟踪用户是否在底部
        private const double ScrollThreshold = 50.0; // 距离底部的阈值（像素）

        public MainWindow()
        {
            InitializeComponent();
            DataContextChanged += MainWindow_DataContextChanged;
        }

        private void MainWindow_DataContextChanged(object? sender, EventArgs e)
        {
            if (DataContext is MainWindowViewModel vm)
            {
                vm.RequestScrollToBottom += ViewModel_RequestScrollToBottom;

                // 订阅文件选择请求事件
                vm.RequestFileSelection += async () =>
                {
                    var files = await StorageProvider.OpenFilePickerAsync(new FilePickerOpenOptions
                    {
                        Title = "选择文件",
                        AllowMultiple = false,
                        FileTypeFilter = new[] { FilePickerFileTypes.All }
                    });
                    return files;
                };
            }

            // 初始化滚动视图的滚动事件监听
            if (ChatMessagesScrollViewer != null)
            {
                ChatMessagesScrollViewer.ScrollChanged += ChatMessagesScrollViewer_ScrollChanged;
            }
        }

        private void ChatMessagesScrollViewer_ScrollChanged(object? sender, ScrollChangedEventArgs e)
        {
            if (sender is ScrollViewer scrollViewer)
            {
                // 检查用户是否在底部（考虑一个小的阈值，避免浮点数精度问题）
                var offset = scrollViewer.Offset.Y;
                var extent = scrollViewer.Extent.Height;
                var viewport = scrollViewer.Viewport.Height;
                
                // 处理边界情况：如果内容高度小于视口高度，认为在底部
                if (extent <= viewport)
                {
                    _isUserAtBottom = true;
                    return;
                }
                
                var distanceFromBottom = extent - (offset + viewport);

                // 如果距离底部小于阈值，认为用户在底部
                _isUserAtBottom = distanceFromBottom <= ScrollThreshold;
            }
        }

        private void ViewModel_RequestScrollToBottom()
        {
            Dispatcher.UIThread.InvokeAsync(() =>
            {
                // 只在用户已经在底部时才自动滚动
                // 这样如果用户向上滚动查看历史消息，就不会被强制拉回底部
                if (_isUserAtBottom)
                {
                    ChatMessagesScrollViewer.ScrollToEnd();
                }
            });
        }

        private void OnDeleteSessionClick(object? sender, RoutedEventArgs e)
        {
            if (sender is Button button && button.Tag is string sessionId)
            {
                if (DataContext is MainWindowViewModel vm)
                {
                    vm.DeleteSessionCommand.Execute(sessionId);
                }
            }
        }
    }
}