MonoTouch Swipe Event

ViewExtensions.cs

using System.Collections.Generic;
using MonoTouch.Foundation;
using MonoTouch.ObjCRuntime;
using MonoTouch.UIKit;

namespace iOSLib
{
    public static class ViewExtensions
    {
        static Dictionary<UIView, Dictionary<UISwipeGestureRecognizerDirection, SwipeClass>>
            views = new Dictionary<UIView, Dictionary<UISwipeGestureRecognizerDirection, SwipeClass>>();

        public class SwipeClass : NSObject
        {
            public class RecognizerDelegate : UIGestureRecognizerDelegate
            {
                public override bool ShouldReceiveTouch(UIGestureRecognizer recognizer, UITouch touch)
                {
                    return true;
                }
            }

            public readonly UIView View;
            Selector selector = new Selector("Swipe");

            public delegate void D(SwipeClass sender, UISwipeGestureRecognizer recognizer);
            public event D Event = delegate { };

            internal SwipeClass(UIView view)
            {
                View = view;
            }

            internal void InitSwipe(UISwipeGestureRecognizerDirection direction)
            {
                if (!View.RespondsToSelector(selector))
                {
                    var swipe = new UISwipeGestureRecognizer();
                    swipe.AddTarget(this, selector);
                    swipe.Direction = direction;
                    swipe.Delegate = new RecognizerDelegate();
                    View.AddGestureRecognizer(swipe);
                }
            }

            [Export("Swipe")]
            void SwipeAction(UISwipeGestureRecognizer recognizer)
            {
                var e = Event;
                e(this, recognizer);
            }
        }

        /// <summary>
        /// Add a swipe event to a View easily, 
        /// and pass the direction and then tack on .Event += ...
        /// </summary>
        /// <param name="view"></param>
        /// <param name="direction"></param>
        /// <returns></returns>
        public static SwipeClass Swipe(this UIView view, UISwipeGestureRecognizerDirection direction)
        {
            Dictionary<UISwipeGestureRecognizerDirection, SwipeClass> inner;
            SwipeClass swipe;
            if (!views.ContainsKey(view))
            {
                views.Add(view, inner = new Dictionary<UISwipeGestureRecognizerDirection, SwipeClass>());
                // need a way to know when view is disposed, so can remove from views so GC
                // can collect it.
            }
            else
                inner = views[view];
            if (!inner.ContainsKey(direction))
                inner.Add(direction, swipe = new SwipeClass(view));
            else
                swipe = inner[direction];
            swipe.InitSwipe(direction);
            return swipe;
        }
    }
}