MainWindowViewModel.cs

using System;
using System.Diagnostics;
using System.Linq;
using System.Windows;
using System.Windows.Threading;
using Livet;

namespace Karno.Xac.Sample
{
    public class MainWindowViewModel : ViewModel
    {
        private readonly DispatcherCollection<string> _collection =
            new DispatcherCollection<string>(DispatcherHelper.UIDispatcher);

        private readonly Stopwatch _stopwatch;

        private readonly DispatcherTimer _timer;

        private readonly DragAcceptDescription _description;

        public DispatcherCollection<string> Collection
        {
            get { return this._collection; }
        }

        public DragAcceptDescription Description
        {
            get { return this._description; }
        }

        public double CurrentTimeSec
        {
            get { return _stopwatch.ElapsedMilliseconds / 1000.0; }
        }

        public MainWindowViewModel()
        {
			// prepare drag accept description
            this._description = new DragAcceptDescription();
            this._description.DragOver += this.OnDragOver;
            this._description.DragDrop += this.OnDragDrop;

            // start tick count
            _stopwatch = new Stopwatch();
            _timer = new DispatcherTimer(DispatcherPriority.Render)
            {
                Interval = TimeSpan.FromMilliseconds(10)
            };
            _timer.Tick += (_, e) => RaisePropertyChanged(() => CurrentTimeSec);
            _timer.Start();

            // create list
            var rand = new Random(Environment.TickCount);
            "にゃんぱすー"
                .Select(c => c.ToString())
                .OrderBy(_ => rand.Next())
                .ForEach(_collection.Add);
        }

        public void Loaded()
        {
            _stopwatch.Start();
        }

        private void OnDragOver(DragEventArgs args)
        {
            if (args.AllowedEffects.HasFlag(DragDropEffects.Move) &&
                args.Data.GetDataPresent(typeof(String)))
            {
                args.Effects = DragDropEffects.Move;
            }
        }

        void OnDragDrop(DragEventArgs args)
        {
            // check and get data
            if (!args.Data.GetDataPresent(typeof(String))) return;
            var data = args.Data.GetData(typeof(String)) as string;
            if (data == null) return;
            var fe = args.OriginalSource as FrameworkElement;
            if (fe == null) return;
            var target = fe.DataContext as string;
            if (target == null) return;

            // move data
            var si = _collection.IndexOf(data);
            var di = _collection.IndexOf(target);
            if (si < 0 || di < 0 || si == di) return;
            _collection.Move(si, di);

            // check にゃんぱすー
            if (_collection.Select(s => s[0]).SequenceEqual("にゃんぱすー"))
            {
                Stop();
            }
        }

        private void Stop()
        {
            _stopwatch.Stop();
            _timer.Stop();
        }
    }
}