ListBox などの項目のドラッグアンドドロップ移動のビヘイビア

DragDropBehavior.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using System.Windows;
using System.Windows.Controls.Primitives;
using System.Windows.Input;
using System.Windows.Interactivity;
using System.Windows.Media;

namespace Ignition.Presentation
{
	public class DragDropBehavior : Behavior<Selector>
	{
		readonly CompositeDisposable observer = new CompositeDisposable();

		protected override void OnAttached()
		{
			observer.Add(Observable.FromEvent<MouseButtonEventHandler, MouseButtonEventArgs>(_ => (sender, e) => _(e), _ => this.AssociatedObject.PreviewMouseDown += _, _ => this.AssociatedObject.PreviewMouseDown -= _)
								   .Where(_ => _.LeftButton == MouseButtonState.Pressed && this.AssociatedObject.ContainerFromElement((DependencyObject)_.OriginalSource) != null)
								   .Select(_ => _.GetPosition(this.AssociatedObject))
								   .SelectMany(pt => Observable.FromEvent<MouseEventHandler, MouseEventArgs>(_ => (sender, e) => _(e), _ => this.AssociatedObject.PreviewMouseMove += _, _ => this.AssociatedObject.PreviewMouseMove -= _)
															   .TakeUntil(Observable.FromEvent<MouseButtonEventHandler, MouseButtonEventArgs>(_ => (sender, e) => _(e), _ => this.AssociatedObject.PreviewMouseUp += _, _ => this.AssociatedObject.PreviewMouseUp -= _))
															   .Select(_ => new
															   {
																   Items = this.AssociatedObject.Items.Cast<object>().Select(i => new
																   {
																	   Container = this.AssociatedObject.ItemContainerGenerator.ContainerFromItem(i),
																	   Item = i
																   }).Where(i => Selector.GetIsSelected(i.Container)).Select(i => i.Item).ToArray(),
																   Vector = pt - _.GetPosition(this.AssociatedObject),
															   })
															   .Where(_ => Math.Abs(_.Vector.X) > SystemParameters.MinimumHorizontalDragDistance || Math.Abs(_.Vector.Y) > SystemParameters.MinimumVerticalDragDistance)
															   .Take(1))
								   .Subscribe(e =>
								   {
									   using (Observable.FromEvent<DragEventHandler, DragEventArgs>(_ => (sender, e2) => _(e2), _ => this.AssociatedObject.Drop += _, _ => this.AssociatedObject.Drop -= _)
														.Where(_ => _.Data.GetDataPresent(typeof(DragDropInfo)))
														.Select(_ => new
														{
															EventArgs = _,
															Data = (DragDropInfo)_.Data.GetData(typeof(DragDropInfo)),
														})
														.Subscribe(p =>
														{
															var list = this.AssociatedObject.ItemsSource as IList ?? this.AssociatedObject.Items;
															var item = list.Cast<object>().Select((_, i) => new
															{
																Container = _ as FrameworkElement ?? (FrameworkElement)this.AssociatedObject.ItemContainerGenerator.ContainerFromIndex(i),
																Item = _,
															})
															.Where(_ => _.Container != null)
															.LastOrDefault(_ => VisualTreeHelper.HitTest(_.Container, p.EventArgs.GetPosition(_.Container)) != null);

															if (item == null)
																foreach (var i in p.Data.Items)
																{
																	list.Remove(i);
																	list.Add(i);
																}
															else
																foreach (var i in p.Data.Items.Where(_ => _ != item.Item && !object.Equals(_, item.Item)))
																{
																	list.Remove(i);
																	list.Insert(list.IndexOf(item.Item), i);
																}
														}))
									   {
										   var ad = this.AssociatedObject.AllowDrop;

										   this.AssociatedObject.AllowDrop = true;
										   DragDrop.DoDragDrop(this.AssociatedObject, new DragDropInfo(e.Items), DragDropEffects.Move);
										   this.AssociatedObject.AllowDrop = ad;
									   }
								   }));
			base.OnAttached();
		}

		protected override void OnDetaching()
		{
			observer.Dispose();
			base.OnDetaching();
		}

		class DragDropInfo
		{
			public IEnumerable<object> Items
			{
				get;
				private set;
			}

			public DragDropInfo(IEnumerable<object> items)
			{
				this.Items = items;
			}
		}
	}
}