JensKrumsieck/ChemSharp

using System.Collections;
using System.Collections.Specialized;
using System.Windows;
using System.Windows.Media.Media3D;

namespace ChemSharp.Molecules.HelixToolkit.Controls;

public class ItemsVisual3D : ModelVisual3D
{
    public static readonly DependencyProperty ItemsSourceProperty = DependencyProperty.Register(
     "ItemsSource",
     typeof(IEnumerable),
     typeof(ItemsVisual3D),
     new PropertyMetadata(null, (s, e) => ((ItemsVisual3D)s).ItemsSourceChanged(e)));

    public IEnumerable ItemsSource
    {
        get => (IEnumerable)GetValue(ItemsSourceProperty);
        set => SetValue(ItemsSourceProperty, value);
    }

    private void ItemsSourceChanged(DependencyPropertyChangedEventArgs e)
    {
        if (e.OldValue is INotifyCollectionChanged oldObservableCollection)
            oldObservableCollection.CollectionChanged -= OnCollectionChanged;

        if (e.NewValue is INotifyCollectionChanged observableCollection)
            observableCollection.CollectionChanged += OnCollectionChanged;

        if (ItemsSource == null) return;

        Children.Clear();
        AddItems(ItemsSource);
    }

    private void OnCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
    {
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                AddItems(e.NewItems);
                break;
            case NotifyCollectionChangedAction.Remove:
                RemoveItems(e.OldItems);
                break;
            case NotifyCollectionChangedAction.Replace:
                RemoveItems(e.OldItems);
                AddItems(e.NewItems);
                break;
            case NotifyCollectionChangedAction.Reset:
                Children.Clear();
                AddItems(ItemsSource);
                break;
        }
    }

    private void RemoveItems(IEnumerable items)
    {
        if (items == null) return;

        foreach (var item in items.Cast<Visual3D>()) Children.Remove(item);
    }

    private void AddItems(IEnumerable items)
    {
        if (items == null) return;

        foreach (var item in items.Cast<Visual3D>()) Children.Add(item);
    }
}