DraggableList.cs

using System;

using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;
using System.Collections.Generic;

using System.Linq;

namespace DraggableList
{
	[Activity (Label = "DraggableList", MainLauncher = true, ScreenOrientation = Android.Content.PM.ScreenOrientation.Portrait)]
	public class MainActivity : Activity
	{
		private List<DataItem> data = new List<DataItem> ();

		public class DataItem 
		{
			public int SortOrder {get;set;}
			public string Name {get;set;}
		}

		protected override void OnCreate (Bundle bundle)
		{
			base.OnCreate (bundle);

			// Set our view from the "main" layout resource
			SetContentView (Resource.Layout.Main);

			int i = 0;
			data.Add (new DataItem { SortOrder = i++, Name = "AAA"});
			data.Add (new DataItem { SortOrder = i++, Name = "444"});
			data.Add (new DataItem { SortOrder = i++, Name = "111"});
			data.Add (new DataItem { SortOrder = i++, Name = "222"});
			data.Add (new DataItem { SortOrder = i++, Name = "999"});
			data.Add (new DataItem { SortOrder = i++, Name = "BBB"});
			data.Add (new DataItem { SortOrder = i++, Name = "333"});
			data.Add (new DataItem { SortOrder = i++, Name = "666"});
			data.Add (new DataItem { SortOrder = i++, Name = "777"});
			data.Add (new DataItem { SortOrder = i++, Name = "555"});
			data.Add (new DataItem { SortOrder = i++, Name = "FFF"});
			data.Add (new DataItem { SortOrder = i++, Name = "888"});
			data.Add (new DataItem { SortOrder = i++, Name = "CCC"});
			data.Add (new DataItem { SortOrder = i++, Name = "DDD"});
			data.Add (new DataItem { SortOrder = i++, Name = "EEE"});
	

			ListView listView = FindViewById<ListView> (Resource.Id.listView1);
			listView.Adapter = new ArrayAdapter (this, Resource.Layout.ListViewTemplate1, data.OrderBy(p => p.SortOrder).Select(p => p.Name).ToArray());

			listView.Touch += (object sender, View.TouchEventArgs e) => 
			{
				ListView view = ((ListView)sender);

				if (e.Event.Action == MotionEventActions.Down) 
				{
					var eventData = ClipData.NewPlainText ("drag", view.PointToPosition((int)e.Event.GetX(), (int)e.Event.GetY()).ToString());

					view.StartDrag (eventData, new NullShadowBuilder (view), null, 0);

					e.Handled = true;
				}
			};

			listView.Drag += (object sender, View.DragEventArgs e) => 
			{
				var evt = e.Event;
				ListView view = ((ListView)sender);

				switch (evt.Action) {
				case DragAction.Started:
					e.Handled = true;
					break;
				case DragAction.Entered:
				case DragAction.Exited:
					break;
				case DragAction.Drop:
					int oldPos = int.Parse(e.Event.ClipData.GetItemAt (0).Text);
					int newPos = view.PointToPosition((int)e.Event.GetX(), (int)e.Event.GetY());

					if (oldPos >= 0 && newPos >= 0)
					{
						var oldItem = data.FirstOrDefault(p => p.Name == view.GetItemAtPosition(oldPos).ToString());
						var newItem = data.FirstOrDefault(p => p.Name == view.GetItemAtPosition(newPos).ToString());

						Console.WriteLine("Handle ze Drag.  Move {0} -> {1}", oldItem.SortOrder, newItem.SortOrder);

						int oldSortOrder = oldItem.SortOrder;
						oldItem.SortOrder = newItem.SortOrder;
						newItem.SortOrder = oldSortOrder;

						listView.Adapter = new ArrayAdapter (this, Resource.Layout.ListViewTemplate1, data.OrderBy(p => p.SortOrder).Select(p => p.Name).ToArray());
					}
					else
						Console.WriteLine("Yeah, no.  Something messed up");

					e.Handled = true;
					break;
				case DragAction.Ended:
					e.Handled = true;
					break;
				}
			};
		}
	}
}