Rx 2.0 primitive sample

internal sealed partial class MainWindow
{
    //Image is an object of type System.Windows.Controls.Image from XAML: <Image x:Name="Image" ...
    //Canvas is an object of type System.Windows.Controls.Canvas from XAML: <Canvas x:Name="Canvas" ...

    private IDisposable _unsubscribe;

    public MainWindow()
    {
        InitializeComponent();

        var mouseDownEvents = from e in Observable.FromEventPattern<MouseButtonEventHandler, MouseEventArgs>
            (
                listener => listener.Invoke,
                listener => Image.MouseDown += listener,
                listener => Image.MouseDown -= listener
            )
            select e.EventArgs.GetPosition(Image);

        var mouseMoveEvents = from e in Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>
            (
                listener => listener.Invoke,
                listener => Image.MouseMove += listener,
                listener => Image.MouseMove -= listener
            )
            select e.EventArgs.GetPosition(Canvas);

        var mouseUpEvents = Observable.FromEventPattern<MouseButtonEventHandler, MouseEventArgs>
            (
                listener => listener.Invoke,
                listener => Image.MouseUp += listener,
                listener => Image.MouseUp -= listener
            );

        var mouseLeaveEvents = Observable.FromEventPattern<MouseEventHandler, MouseEventArgs>
            (
                listener => listener.Invoke,
                listener => Image.MouseLeave += listener,
                listener => Image.MouseLeave -= listener
            );

        var dragAndDrops =
            from clickPosition in mouseDownEvents
                from movePosition in mouseMoveEvents.TakeUntil(mouseUpEvents.Merge(mouseLeaveEvents))
                    select new
                    {
                        X = movePosition.X - clickPosition.X,
                        Y = movePosition.Y - clickPosition.Y
                    };

        _unsubscribe = dragAndDrops.ObserveOn(SynchronizationContext.Current).Subscribe(newImagePosition =>
        {
            Canvas.SetLeft(Image, newImagePosition.X);
            Canvas.SetTop(Image, newImagePosition.Y);
        });
    }

    private void StopTracking(object sender, RoutedEventArgs e)
    {
        if (null != _unsubscribe)
        {
            _unsubscribe.Dispose();
            _unsubscribe = null;
        }
    }
}