emby-toolbox/EmbyToolbox/Behaviors/ListBoxAutoScrollBehavior.cs

using System.Collections.Specialized;
using System.Windows;
using System.Windows.Controls;

namespace EmbyToolbox.Behaviors;

public static class ListBoxAutoScrollBehavior
{
    public static readonly DependencyProperty AutoScrollToEndProperty =
        DependencyProperty.RegisterAttached(
            "AutoScrollToEnd",
            typeof(bool),
            typeof(ListBoxAutoScrollBehavior),
            new PropertyMetadata(false, OnAutoScrollToEndChanged));

    public static bool GetAutoScrollToEnd(DependencyObject obj)
    {
        return (bool)obj.GetValue(AutoScrollToEndProperty);
    }

    public static void SetAutoScrollToEnd(DependencyObject obj, bool value)
    {
        obj.SetValue(AutoScrollToEndProperty, value);
    }

    private static void OnAutoScrollToEndChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is not ListBox listBox)
        {
            return;
        }

        if ((bool)e.NewValue)
        {
            listBox.Loaded += ListBoxOnLoaded;
        }
        else
        {
            listBox.Loaded -= ListBoxOnLoaded;
            UnhookCollection(listBox);
        }
    }

    private static void ListBoxOnLoaded(object sender, RoutedEventArgs e)
    {
        if (sender is not ListBox listBox)
        {
            return;
        }

        HookCollection(listBox);
        ScrollToLast(listBox);
    }

    private static void HookCollection(ListBox listBox)
    {
        if (listBox.ItemsSource is INotifyCollectionChanged collection)
        {
            collection.CollectionChanged -= OnCollectionChanged;
            collection.CollectionChanged += OnCollectionChanged;
        }
    }

    private static void UnhookCollection(ListBox listBox)
    {
        if (listBox.ItemsSource is INotifyCollectionChanged collection)
        {
            collection.CollectionChanged -= OnCollectionChanged;
        }
    }

    private static void OnCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
    {
        if (sender is not INotifyCollectionChanged collection)
        {
            return;
        }

        foreach (Window window in Application.Current.Windows)
        {
            var listBox = FindListBoxForCollection(window, collection);
            if (listBox is not null)
            {
                ScrollToLast(listBox);
                return;
            }
        }
    }

    private static ListBox? FindListBoxForCollection(DependencyObject root, INotifyCollectionChanged collection)
    {
        if (root is ListBox listBox && ReferenceEquals(listBox.ItemsSource, collection))
        {
            return listBox;
        }

        var childrenCount = System.Windows.Media.VisualTreeHelper.GetChildrenCount(root);
        for (var i = 0; i < childrenCount; i++)
        {
            var child = System.Windows.Media.VisualTreeHelper.GetChild(root, i);
            var found = FindListBoxForCollection(child, collection);
            if (found is not null)
            {
                return found;
            }
        }

        return null;
    }

    private static void ScrollToLast(ListBox listBox)
    {
        if (listBox.Items.Count <= 0)
        {
            return;
        }

        var last = listBox.Items[listBox.Items.Count - 1];
        listBox.ScrollIntoView(last);
    }
}