Carousel clean (#135)

CarouselView moving to preview repo

1 files changed, 0 insertions, 1246 deletions

diff --git a/Xamarin.Forms.Platform.Android/Renderers/CarouselViewRenderer.cs b/Xamarin.Forms.Platform.Android/Renderers/CarouselViewRenderer.cs
deleted file mode 100644
index 7b0da7aa..00000000
--- a/Xamarin.Forms.Platform.Android/Renderers/CarouselViewRenderer.cs
+++ /dev/null
@@ -1,1246 +0,0 @@
-using System;
-using System.Collections.Specialized;
-using System.ComponentModel;
-using System.Collections.Generic;
-using System.Linq;
-using Android.Content;
-using Android.Graphics;
-using Android.Views;
-using Android.Support.V7.Widget;
-using static System.Diagnostics.Debug;
-using IntRectangle = System.Drawing.Rectangle;
-using IntSize = System.Drawing.Size;
-using IntPoint = System.Drawing.Point;
-using AndroidView = Android.Views.View;
-using Adapter = Android.Support.V7.Widget.RecyclerView.Adapter;
-using Recycler = Android.Support.V7.Widget.RecyclerView.Recycler;
-using State = Android.Support.V7.Widget.RecyclerView.State;
-using ViewHolder = Android.Support.V7.Widget.RecyclerView.ViewHolder;
-using Observer = Android.Support.V7.Widget.RecyclerView.AdapterDataObserver;
-using LayoutManager = Android.Support.V7.Widget.RecyclerView.LayoutManager;
-using LayoutParams = Android.Support.V7.Widget.RecyclerView.LayoutParams;
-
-namespace Xamarin.Forms.Platform.Android
-{
-	internal static class CarouselViewExtensions
-	{
-		internal static IntVector BoundTranslation(this IntRectangle viewport, IntVector delta, IntRectangle bound)
-		{
-			// TODO: generalize the math
-			Assert(delta.X == 0 || delta.Y == 0);
-
-			IntVector start = viewport.LeadingCorner(delta);
-			IntVector end = start + delta;
-			IntVector clampedEnd = end.Clamp(bound);
-			IntVector clampedDelta = clampedEnd - start;
-			return clampedDelta;
-		}
-		internal static IntVector Clamp(this IntVector position, IntRectangle bound)
-		{
-			return new IntVector(
-				x: position.X.Clamp(bound.Left, bound.Right),
-				y: position.Y.Clamp(bound.Top, bound.Bottom)
-			);
-		}
-		internal static IntVector LeadingCorner(this IntRectangle rectangle, IntVector delta)
-		{
-			return new IntVector(
-				x: delta.X < 0 ? rectangle.Left : rectangle.Right,
-				y: delta.Y < 0 ? rectangle.Top : rectangle.Bottom
-			);
-		}
-		internal static IntVector Center(this IntRectangle rectangle)
-		{
-			return (IntVector)rectangle.Location + (IntVector)rectangle.Size / 2;
-		}
-		internal static int Area(this IntRectangle rectangle)
-		{
-			return rectangle.Width * rectangle.Height;
-		}
-
-		internal static Rectangle ToFormsRectangle(this IntRectangle rectangle, Context context)
-		{
-			return new Rectangle(
-				x: context.FromPixels(rectangle.Left),
-				y: context.FromPixels(rectangle.Top),
-				width: context.FromPixels(rectangle.Width),
-				height: context.FromPixels(rectangle.Height)
-			);
-		}
-		internal static Rect ToAndroidRectangle(this IntRectangle rectangle)
-		{
-			return new Rect(
-				left: rectangle.Left,
-				right: rectangle.Right,
-				top: rectangle.Top,
-				bottom: rectangle.Bottom
-			);
-		}
-
-		internal static bool LexicographicallyLess(this IntPoint source, IntPoint target)
-		{
-			if (source.X < target.X)
-				return true;
-
-			if (source.X > target.X)
-				return false;
-
-			return source.Y < target.Y;
-		}
-		internal static int[] ToRange(this Tuple<int, int> startAndCount)
-		{
-			return Enumerable.Range(startAndCount.Item1, startAndCount.Item2).ToArray();
-		}
-	}
-
-	internal struct IntVector
-	{
-		public static explicit operator IntVector(IntSize size)
-		{
-			return new IntVector(size.Width, size.Height);
-		}
-		public static explicit operator IntVector(IntPoint point)
-		{
-			return new IntVector(point.X, point.Y);
-		}
-		public static implicit operator IntPoint(IntVector vector)
-		{
-			return new IntPoint(vector.X, vector.Y);
-		}
-		public static implicit operator IntSize(IntVector vector)
-		{
-			return new IntSize(vector.X, vector.Y);
-		}
-
-		public static bool operator ==(IntVector lhs, IntVector rhs)
-		{
-			return lhs.X == rhs.X && lhs.Y == rhs.Y;
-		}
-		public static bool operator !=(IntVector lhs, IntVector rhs)
-		{
-			return !(lhs == rhs);
-		}
-		public static IntRectangle operator -(IntRectangle source, IntVector vector) => source + -vector;
-		public static IntRectangle operator +(IntRectangle source, IntVector vector) =>
-			new IntRectangle(source.Location + vector, source.Size);
-
-		public static IntVector operator -(IntVector vector, IntVector other) => vector + -other;
-		public static IntVector operator +(IntVector vector, IntVector other) =>
-			new IntVector(
-				x: vector.X + other.X,
-				y: vector.Y + other.Y
-			);
-
-		public static IntPoint operator -(IntPoint point, IntVector delta) => point + -delta;
-		public static IntPoint operator +(IntPoint point, IntVector delta) =>
-			new IntPoint(
-				x: point.X + delta.X,
-				y: point.Y + delta.Y
-			);
-
-		public static IntVector operator -(IntVector vector) => vector * -1;
-		public static IntVector operator *(IntVector vector, int scaler) =>
-			new IntVector(
-				x: vector.X * scaler,
-				y: vector.Y * scaler
-			);
-		public static IntVector operator /(IntVector vector, int scaler) =>
-			new IntVector(
-				x: vector.X / scaler,
-				y: vector.Y / scaler
-			);
-
-		public static IntVector operator *(IntVector vector, double scaler) =>
-			new IntVector(
-				x: (int)(vector.X * scaler),
-				y: (int)(vector.Y * scaler)
-			);
-		public static IntVector operator /(IntVector vector, double scaler) => vector * (1 / scaler);
-
-		internal static IntVector Origin = new IntVector(0, 0);
-		internal static IntVector XUnit = new IntVector(1, 0);
-		internal static IntVector YUnit = new IntVector(0, 1);
-
-		#region Fields
-		readonly int _x;
-		readonly int _y;
-		#endregion
-
-		internal IntVector(int x, int y)
-		{
-			_x = x;
-			_y = y;
-		}
-
-		internal int X => _x;
-		internal int Y => _y;
-
-		public override bool Equals(object obj)
-		{
-			return base.Equals(obj);
-		}
-		public override int GetHashCode()
-		{
-			return base.GetHashCode();
-		}
-		public override string ToString()
-		{
-			return $"{X},{Y}";
-		}
-	}
-
-	[Flags]
-	internal enum MeasureSpecificationType
-	{
-		Unspecified = 0,
-		Exactly = 0x1 << 31,
-		AtMost = 0x1 << 32,
-		Mask = Exactly | AtMost
-	}
-	internal struct MeasureSpecification
-	{
-		public static explicit operator MeasureSpecification(int measureSpecification)
-		{
-			return new MeasureSpecification(measureSpecification);
-		}
-		public static implicit operator int(MeasureSpecification measureSpecification)
-		{
-			return measureSpecification.Encode();
-		}
-
-		#region Fields
-		readonly int _value;
-		readonly MeasureSpecificationType _type;
-		#endregion
-
-		internal MeasureSpecification(int measureSpecification)
-		{
-			_value = measureSpecification & (int)~MeasureSpecificationType.Mask;
-			_type = (MeasureSpecificationType)(measureSpecification & (int)MeasureSpecificationType.Mask);
-		}
-		internal MeasureSpecification(int value, MeasureSpecificationType measureSpecification)
-		{
-			_value = value;
-			_type = measureSpecification;
-		}
-
-		internal int Value => _value;
-		internal MeasureSpecificationType Type => _type;
-		internal int Encode() => Value | (int)Type;
-
-		public override string ToString()
-		{
-			return string.Format("{0} {1}", Value, Type);
-		}
-	}
-
-	public class CarouselViewRenderer : ViewRenderer<CarouselView, RecyclerView>
-	{
-		// http://developer.android.com/reference/android/support/v7/widget/RecyclerView.html
-		// http://developer.android.com/training/material/lists-cards.html
-		// http://wiresareobsolete.com/2014/09/building-a-recyclerview-layoutmanager-part-1/
-
-		internal class VirtualLayoutManager : PhysicalLayoutManager.VirtualLayoutManager
-		{
-			#region Fields
-			const int Columns = 1;
-			IntSize _itemSize;
-			#endregion
-
-			#region Private Members
-			int GetPosition(int itemCount, int positionOrigin, int x, bool exclusive = false)
-			{
-				int position = x / _itemSize.Width + positionOrigin;
-				bool hasRemainder = x % _itemSize.Width != 0;
-
-				if (hasRemainder && x < 0)
-					position--;
-
-				if (!hasRemainder && exclusive)
-					position--;
-
-				position = position.Clamp(0, itemCount - 1);
-				return position;
-			}
-			#endregion
-
-			internal override bool CanScrollHorizontally => true;
-			internal override bool CanScrollVertically => false;
-
-			internal override IntRectangle GetBounds(int originPosition, State state) =>
-				new IntRectangle(
-					LayoutItem(originPosition, 0).Location,
-					new IntSize(_itemSize.Width * state.ItemCount, _itemSize.Height)
-				);
-
-			internal override Tuple<int, int> GetPositions(
-				int positionOrigin,
-				int itemCount,
-				IntRectangle viewport,
-				bool includeBuffer)
-			{
-				// returns one item off-screen in either direction. 
-				int buffer = includeBuffer ? 1 : 0;
-				int left = GetPosition(itemCount, positionOrigin - buffer, viewport.Left);
-				int right = GetPosition(itemCount, positionOrigin + buffer, viewport.Right, exclusive: true);
-
-				int start = left;
-				int count = right - left + 1;
-				return new Tuple<int, int>(start, count);
-			}
-			internal override void Layout(int positionOffset, IntSize viewportSize, ref IntVector offset)
-			{
-				int width = viewportSize.Width / Columns;
-				int height = viewportSize.Height;
-
-				if (_itemSize.Width != 0)
-					offset *= (double)width / _itemSize.Width;
-
-				_itemSize = new IntSize(width, height);
-			}
-			internal override IntRectangle LayoutItem(int positionOffset, int position)
-			{
-				// measure
-				IntSize size = _itemSize;
-
-				// layout
-				var location = new IntVector((position - positionOffset) * size.Width, 0);
-
-				// allocate
-				return new IntRectangle(location, size);
-			}
-
-			public override string ToString()
-			{
-				return $"itemSize={_itemSize}";
-			}
-		}
-
-		#region Private Definitions
-		class OnScrollListener : RecyclerView.OnScrollListener
-		{
-			enum ScrollState
-			{
-				Idle,
-				Dragging,
-				Settling
-			}
-
-			readonly Action _onDragEnd;
-			readonly Action _onDragStart;
-			ScrollState _lastScrollState;
-
-			internal OnScrollListener(
-				Action onDragEnd,
-				Action onDragStart)
-			{
-				_onDragEnd = onDragEnd;
-				_onDragStart = onDragStart;
-			}
-
-			public override void OnScrollStateChanged(RecyclerView recyclerView, int newState)
-			{
-				var state = (ScrollState)newState;
-				if (_lastScrollState != ScrollState.Dragging && state == ScrollState.Dragging)
-					_onDragStart();
-
-				if (_lastScrollState == ScrollState.Dragging && state != ScrollState.Dragging)
-					_onDragEnd();
-
-				_lastScrollState = state;
-				base.OnScrollStateChanged(recyclerView, newState);
-			}
-		}
-		class PositionUpdater : Observer
-		{
-			#region Fields
-			readonly CarouselViewRenderer _carouselView;
-			#endregion
-
-			internal PositionUpdater(CarouselViewRenderer carouselView)
-			{
-				_carouselView = carouselView;
-			}
-
-			public override void OnItemRangeInserted(int positionStart, int itemCount)
-			{
-				if (positionStart > _carouselView._position)
-				{
-					// removal after the current position won't change current position
-				}
-				else
-				{
-					// raise position changed
-					_carouselView._position += itemCount;
-					_carouselView.OnPositionChanged();
-				}
-
-				base.OnItemRangeInserted(positionStart, itemCount);
-			}
-			public override void OnItemRangeRemoved(int positionStart, int itemCount)
-			{
-				Assert(itemCount == 1);
-
-				if (positionStart > _carouselView._position)
-				{
-					// removal after the current position won't change current position
-				}
-				else if (positionStart == _carouselView._position &&
-					positionStart != _carouselView.Adapter.ItemCount)
-				{
-					// raise item changed
-					_carouselView.OnItemChanged();
-					return;
-				}
-				else
-				{
-					// raise position changed
-					_carouselView._position -= itemCount;
-					_carouselView.OnPositionChanged();
-				}
-
-				base.OnItemRangeRemoved(positionStart, itemCount);
-			}
-		}
-		#endregion
-
-		#region Fields
-		PhysicalLayoutManager _physicalLayout;
-		int _position;
-		bool _disposed;
-		#endregion
-
-		public CarouselViewRenderer()
-		{
-			AutoPackage = false;
-		}
-
-		protected override void Dispose(bool disposing)
-		{
-			if (disposing && !_disposed)
-			{
-				_disposed = true;
-				if (Element != null)
-					Element.CollectionChanged -= OnCollectionChanged;
-			}
-
-			base.Dispose(disposing);
-		}
-
-		#region Private Members
-		void Initialize()
-		{
-			// cache hit? Check if the view page is already created
-			RecyclerView recyclerView = Control;
-			if (recyclerView != null)
-				return;
-
-			// cache miss
-			recyclerView = new RecyclerView(Context);
-			SetNativeControl(recyclerView);
-
-			// layoutManager
-			recyclerView.SetLayoutManager(
-				layout: _physicalLayout = new PhysicalLayoutManager(
-					context: Context,
-					virtualLayout: new VirtualLayoutManager(),
-					positionOrigin: Element.Position
-				)
-			);
-
-			// swiping
-			var dragging = false;
-			recyclerView.AddOnScrollListener(
-				new OnScrollListener(
-					onDragStart: () => dragging = true,
-					onDragEnd: () =>
-					{
-						dragging = false;
-						var velocity = _physicalLayout.Velocity;
-
-						var target = velocity.X > 0 ?
-							_physicalLayout.VisiblePositions().Max() :
-							_physicalLayout.VisiblePositions().Min();
-						_physicalLayout.ScrollToPosition(target);
-					}
-				)
-			);
-
-			// scrolling
-			var scrolling = false;
-			_physicalLayout.OnBeginScroll += position => scrolling = true;
-			_physicalLayout.OnEndScroll += position => scrolling = false;
-
-			// appearing
-			_physicalLayout.OnAppearing += appearingPosition =>
-			{
-				Controller.SendPositionAppearing(appearingPosition);
-			};
-
-			// disappearing
-			_physicalLayout.OnDisappearing += disappearingPosition =>
-			{
-				Controller.SendPositionDisappearing(disappearingPosition);
-
-				// animation completed
-				if (!scrolling && !dragging)
-				{
-					_position = _physicalLayout.VisiblePositions().Single();
-
-					OnPositionChanged();
-					OnItemChanged();
-				}
-			};
-
-			// adapter
-			var adapter = new ItemViewAdapter(this);
-			adapter.RegisterAdapterDataObserver(new PositionUpdater(this));
-			recyclerView.SetAdapter(adapter);
-		}
-
-		ItemViewAdapter Adapter => (ItemViewAdapter)Control.GetAdapter();
-		PhysicalLayoutManager LayoutManager => (PhysicalLayoutManager)Control.GetLayoutManager();
-
-		void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
-		{
-			switch (e.Action)
-			{
-				case NotifyCollectionChangedAction.Add:
-					Adapter.NotifyItemRangeInserted(
-						positionStart: e.NewStartingIndex,
-						itemCount: e.NewItems.Count
-					);
-					break;
-
-				case NotifyCollectionChangedAction.Move:
-					for (var i = 0; i < e.NewItems.Count; i++)
-						Adapter.NotifyItemMoved(
-							fromPosition: e.OldStartingIndex + i,
-							toPosition: e.NewStartingIndex + i
-						);
-					break;
-
-				case NotifyCollectionChangedAction.Remove:
-					if (Controller.Count == 0)
-						throw new InvalidOperationException("CarouselView must retain a least one item.");
-
-					Adapter.NotifyItemRangeRemoved(
-						positionStart: e.OldStartingIndex,
-						itemCount: e.OldItems.Count
-					);
-					break;
-
-				case NotifyCollectionChangedAction.Replace:
-					Adapter.NotifyItemRangeChanged(
-						positionStart: e.OldStartingIndex,
-						itemCount: e.OldItems.Count
-					);
-					break;
-
-				case NotifyCollectionChangedAction.Reset:
-					Adapter.NotifyDataSetChanged();
-					break;
-
-				default:
-					throw new Exception($"Enum value '{(int)e.Action}' is not a member of NotifyCollectionChangedAction enumeration.");
-			}
-		}
-		ICarouselViewController Controller => Element;
-		IVisualElementController VisualElementController => Element;
-		void OnPositionChanged()
-		{
-			Element.Position = _position;
-			Controller.SendSelectedPositionChanged(_position);
-		}
-		void OnItemChanged()
-		{
-			object item = ((IItemViewController)Element).GetItem(_position);
-			Controller.SendSelectedItemChanged(item);
-		}
-		#endregion
-
-		protected override void OnElementChanged(ElementChangedEventArgs<CarouselView> e)
-		{
-			base.OnElementChanged(e);
-
-			CarouselView oldElement = e.OldElement;
-			CarouselView newElement = e.NewElement;
-			if (oldElement != null)
-			{
-				e.OldElement.CollectionChanged -= OnCollectionChanged;
-			}
-
-			if (newElement != null)
-			{
-				if (Control == null)
-				{
-					Initialize();
-				}
-
-				// initialize properties
-				_position = Element.Position;
-
-				// initialize events
-				Element.CollectionChanged += OnCollectionChanged;
-			}
-		}
-		protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
-		{
-			if (e.PropertyName == "Position" && _position != Element.Position)
-				_physicalLayout.ScrollToPosition(Element.Position);
-
-			base.OnElementPropertyChanged(sender, e);
-		}
-		protected override void OnLayout(bool changed, int left, int top, int right, int bottom)
-		{
-			int width = right - left;
-			int height = bottom - top;
-
-			LayoutManager.Layout(width, height);
-
-			base.OnLayout(changed, left, top, right, bottom);
-
-			Control.Measure(
-				widthMeasureSpec: new MeasureSpecification(width, MeasureSpecificationType.Exactly),
-				heightMeasureSpec: new MeasureSpecification(height, MeasureSpecificationType.Exactly)
-			);
-
-			Control.Layout(0, 0, width, height);
-		}
-		protected override Size MinimumSize()
-		{
-			return new Size(40, 40);
-		}
-	}
-
-	// RecyclerView virtualizes indexes (adapter position <-> viewGroup child index) 
-	// PhysicalLayoutManager virtualizes location (regular layout <-> screen)
-	internal class PhysicalLayoutManager : LayoutManager
-	{
-		// ObservableCollection is our public entryway to this method and it only supports single item removal
-		internal const int MaxItemsRemoved = 1;
-
-		internal struct DecoratedView
-		{
-			public static implicit operator AndroidView(DecoratedView view)
-			{
-				return view._view;
-			}
-
-			#region Fields
-			readonly PhysicalLayoutManager _layout;
-			readonly AndroidView _view;
-			#endregion
-
-			internal DecoratedView(
-				PhysicalLayoutManager layout,
-				AndroidView view)
-			{
-				_layout = layout;
-				_view = view;
-			}
-
-			internal int Left => _layout.GetDecoratedLeft(_view);
-			internal int Top => _layout.GetDecoratedTop(_view);
-			internal int Bottom => _layout.GetDecoratedBottom(_view);
-			internal int Right => _layout.GetDecoratedRight(_view);
-			internal int Width => Right - Left;
-			internal int Height => Bottom - Top;
-			internal IntRectangle Rectangle => new IntRectangle(Left, Top, Width, Height);
-
-			internal void Measure(int widthUsed, int heightUsed)
-			{
-				_layout.MeasureChild(_view, widthUsed, heightUsed);
-			}
-			internal void MeasureWithMargins(int widthUsed, int heightUsed)
-			{
-				_layout.MeasureChildWithMargins(_view, widthUsed, heightUsed);
-			}
-			internal void Layout(IntRectangle position)
-			{
-				var renderer = _view as IVisualElementRenderer;
-				renderer.Element.Layout(position.ToFormsRectangle(_layout._context));
-
-				// causes the private LAYOUT_REQUIRED flag to be set so we can be sure the Layout call will properly chain through to all children
-				Measure(position.Width, position.Height);
-				_layout.LayoutDecorated(_view,
-					left: position.Left,
-					top: position.Top,
-					right: position.Right,
-					bottom: position.Bottom
-				);
-			}
-			internal void Add()
-			{
-				_layout.AddView(_view);
-			}
-			internal void DetachAndScrap(Recycler recycler)
-			{
-				_layout.DetachAndScrapView(_view, recycler);
-			}
-		}
-		internal abstract class VirtualLayoutManager
-		{
-			internal abstract Tuple<int, int> GetPositions(
-				int positionOrigin,
-				int itemCount,
-				IntRectangle viewport,
-				bool isPreLayout
-			);
-
-			internal abstract IntRectangle LayoutItem(int positionOrigin, int position);
-			internal abstract bool CanScrollHorizontally
-			{
-				get;
-			}
-			internal abstract bool CanScrollVertically
-			{
-				get;
-			}
-
-			internal abstract void Layout(int positionOrigin, IntSize viewportSize, ref IntVector offset);
-			internal abstract IntRectangle GetBounds(int positionOrigin, State state);
-		}
-
-		#region Private Defintions
-		enum AdapterChangeType
-		{
-			Removed = 1,
-			Added,
-			Moved,
-			Updated,
-			Changed
-		}
-		enum SnapPreference
-		{
-			None = 0,
-			Begin = 1,
-			End = -1
-		}
-		sealed class SeekAndSnapScroller : LinearSmoothScroller
-		{
-			#region Fields
-			readonly SnapPreference _snapPreference;
-			readonly Func<int, IntVector> _vectorToPosition;
-			#endregion
-
-			internal SeekAndSnapScroller(
-				Context context,
-				Func<int, IntVector> vectorToPosition,
-				SnapPreference snapPreference = SnapPreference.None)
-				: base(context)
-			{
-				_vectorToPosition = vectorToPosition;
-				_snapPreference = snapPreference;
-			}
-
-			protected override int HorizontalSnapPreference => (int)_snapPreference;
-			protected override void OnStart()
-			{
-				OnBeginScroll?.Invoke(TargetPosition);
-				base.OnStart();
-			}
-			protected override void OnStop()
-			{
-				// expected this to be triggered with the animation stops but it
-				// actually seems to be triggered when the target is found
-				OnEndScroll?.Invoke(TargetPosition);
-				base.OnStop();
-			}
-
-			public event Action<int> OnBeginScroll;
-			public event Action<int> OnEndScroll;
-
-			public override PointF ComputeScrollVectorForPosition(int targetPosition)
-			{
-				var vector = _vectorToPosition(targetPosition);
-				return new PointF(vector.X, vector.Y);
-			}
-
-		}
-		#endregion
-
-		#region Static Fields
-		readonly static int s_samplesCount = 5;
-		#endregion
-
-		#region Fields
-		readonly Context _context;
-		readonly VirtualLayoutManager _virtualLayout;
-		readonly Queue<Action<Recycler, State>> _deferredLayout;
-		readonly Dictionary<int, AndroidView> _viewByAdaptorPosition;
-		readonly HashSet<int> _visibleAdapterPosition;
-		readonly SeekAndSnapScroller _scroller;
-
-		int _positionOrigin; // coordinates are relative to the upper left corner of this element
-		IntVector _locationOffset; // upper left corner of screen is positionOrigin + locationOffset
-		List<IntVector> _samples;
-		AdapterChangeType _adapterChangeType;
-		#endregion
-
-		internal PhysicalLayoutManager(Context context, VirtualLayoutManager virtualLayout, int positionOrigin)
-		{
-			_positionOrigin = positionOrigin;
-			_context = context;
-			_virtualLayout = virtualLayout;
-			_viewByAdaptorPosition = new Dictionary<int, AndroidView>();
-			_visibleAdapterPosition = new HashSet<int>();
-			_samples = Enumerable.Repeat(IntVector.Origin, s_samplesCount).ToList();
-			_deferredLayout = new Queue<Action<Recycler, State>>();
-			_scroller = new SeekAndSnapScroller(
-				context: context,
-				vectorToPosition: adapterPosition =>
-				{
-					var end = virtualLayout.LayoutItem(_positionOrigin, adapterPosition).Center();
-					var begin = Viewport.Center();
-					return end - begin;
-				}
-			);
-
-			_scroller.OnBeginScroll += adapterPosition => OnBeginScroll?.Invoke(adapterPosition);
-			_scroller.OnEndScroll += adapterPosition => OnEndScroll?.Invoke(adapterPosition);
-		}
-
-		#region Private Members
-		// helpers to deal with locations as IntRectangles and IntVectors
-		IntRectangle Rectangle => new IntRectangle(0, 0, Width, Height);
-		void OffsetChildren(IntVector delta)
-		{
-			OffsetChildrenHorizontal(-delta.X);
-			OffsetChildrenVertical(-delta.Y);
-		}
-		void ScrollBy(ref IntVector delta, Recycler recycler, State state)
-		{
-			_adapterChangeType = default(AdapterChangeType);
-
-			delta = Viewport.BoundTranslation(
-				delta: delta,
-				bound: _virtualLayout.GetBounds(_positionOrigin, state)
-			);
-
-			_locationOffset += delta;
-			_samples.Insert(0, delta);
-			_samples.RemoveAt(_samples.Count - 1);
-
-			OffsetChildren(delta);
-			OnLayoutChildren(recycler, state);
-		}
-		void OnAppearingOrDisappearing(int position, bool isAppearing)
-		{
-			if (isAppearing)
-			{
-				if (!_visibleAdapterPosition.Contains(position))
-				{
-					_visibleAdapterPosition.Add(position);
-					OnAppearing?.Invoke(position);
-				}
-			}
-			else
-			{
-				if (_visibleAdapterPosition.Contains(position))
-				{
-					_visibleAdapterPosition.Remove(position);
-					OnDisappearing?.Invoke(position);
-				}
-			}
-		}
-		#endregion
-
-		protected override void Dispose(bool disposing)
-		{
-			base.Dispose(disposing);
-		}
-
-		internal event Action<int> OnAppearing;
-		internal event Action<int> OnBeginScroll;
-		internal event Action<int> OnDisappearing;
-		internal event Action<int> OnEndScroll;
-
-		internal IntVector Velocity => _samples.Aggregate((o, a) => o + a) / _samples.Count;
-		internal void Layout(int width, int height)
-		{
-			// e.g. when rotated the width and height are updated the virtual layout will 
-			// need to resize and provide a new viewport offset given the current one.
-			_virtualLayout.Layout(_positionOrigin, new IntSize(width, height), ref _locationOffset);
-		}
-		internal IntRectangle Viewport => Rectangle + _locationOffset;
-		internal IEnumerable<int> VisiblePositions()
-		{
-			return _visibleAdapterPosition;
-		}
-		internal IEnumerable<AndroidView> Views()
-		{
-			return _viewByAdaptorPosition.Values;
-		}
-
-		public override void OnAdapterChanged(Adapter oldAdapter, Adapter newAdapter)
-		{
-			RemoveAllViews();
-		}
-		public override void OnItemsChanged(RecyclerView recyclerView)
-		{
-			_adapterChangeType = AdapterChangeType.Changed;
-
-			// low-fidelity change event; assume everything has changed. If adapter reports it has "stable IDs" then 
-			// RecyclerView will attempt to synthesize high-fidelity change events: added, removed, moved, updated.
-			base.OnItemsChanged(recyclerView);
-		}
-		public override void OnItemsAdded(RecyclerView recyclerView, int positionStart, int itemCount)
-		{
-			_adapterChangeType = AdapterChangeType.Added;
-
-			_deferredLayout.Enqueue((recycler, state) =>
-			{
-
-				var viewByAdaptorPositionCopy = _viewByAdaptorPosition.ToArray();
-				_viewByAdaptorPosition.Clear();
-				foreach (KeyValuePair<int, AndroidView> pair in viewByAdaptorPositionCopy)
-				{
-					var view = pair.Value;
-					var position = pair.Key;
-
-					// position unchanged
-					if (position < positionStart)
-						_viewByAdaptorPosition[position] = view;
-
-					// position changed
-					else
-						_viewByAdaptorPosition[position + itemCount] = view;
-				}
-
-				if (_positionOrigin >= positionStart)
-					_positionOrigin += itemCount;
-			});
-			base.OnItemsAdded(recyclerView, positionStart, itemCount);
-		}
-		public override void OnItemsRemoved(RecyclerView recyclerView, int positionStart, int itemCount)
-		{
-			Assert(itemCount == MaxItemsRemoved);
-			_adapterChangeType = AdapterChangeType.Removed;
-
-			var positionEnd = positionStart + itemCount;
-
-			_deferredLayout.Enqueue((recycler, state) =>
-			{
-				if (state.ItemCount == 0)
-					throw new InvalidOperationException("Cannot delete all items.");
-
-				// re-map views to their new positions
-				var viewByAdaptorPositionCopy = _viewByAdaptorPosition.ToArray();
-				_viewByAdaptorPosition.Clear();
-				foreach (var pair in viewByAdaptorPositionCopy)
-				{
-					var view = pair.Value;
-					var position = pair.Key;
-
-					// position unchanged
-					if (position < positionStart)
-						_viewByAdaptorPosition[position] = view;
-
-					// position changed
-					else if (position >= positionEnd)
-						_viewByAdaptorPosition[position - itemCount] = view;
-
-					// removed
-					else
-					{
-						_viewByAdaptorPosition[-1] = view;
-						if (_visibleAdapterPosition.Contains(position))
-							_visibleAdapterPosition.Remove(position);
-					}
-				}
-
-				// if removed origin then shift origin to first removed position
-				if (_positionOrigin >= positionStart && _positionOrigin < positionEnd)
-				{
-					_positionOrigin = positionStart;
-
-					// if no items to right of removed origin then set origin to item prior to removed set
-					if (_positionOrigin >= state.ItemCount)
-					{
-						_positionOrigin = state.ItemCount - 1;
-
-						if (!_viewByAdaptorPosition.ContainsKey(_positionOrigin))
-							throw new InvalidOperationException(
-								"VirtualLayoutManager must add items to the left and right of the origin"
-							);
-					}
-				}
-
-				// if removed before origin then shift origin left
-				else if (_positionOrigin >= positionEnd)
-					_positionOrigin -= itemCount;
-			});
-
-			base.OnItemsRemoved(recyclerView, positionStart, itemCount);
-		}
-		public override void OnItemsMoved(RecyclerView recyclerView, int from, int toValue, int itemCount)
-		{
-			_adapterChangeType = AdapterChangeType.Moved;
-			base.OnItemsMoved(recyclerView, from, toValue, itemCount);
-		}
-		public override void OnItemsUpdated(RecyclerView recyclerView, int positionStart, int itemCount)
-		{
-			_adapterChangeType = AdapterChangeType.Updated;
-
-			// rebind rendered updated elements
-			_deferredLayout.Enqueue((recycler, state) =>
-			{
-				for (var i = 0; i < itemCount; i++)
-				{
-					var position = positionStart + i;
-
-					AndroidView view;
-					if (!_viewByAdaptorPosition.TryGetValue(position, out view))
-						continue;
-
-					recycler.BindViewToPosition(view, position);
-				}
-			});
-
-			base.OnItemsUpdated(recyclerView, positionStart, itemCount);
-		}
-
-		public override LayoutParams GenerateDefaultLayoutParams()
-		{
-			return new LayoutParams(ViewGroup.LayoutParams.WrapContent, ViewGroup.LayoutParams.WrapContent);
-		}
-		public override AndroidView FindViewByPosition(int adapterPosition)
-		{
-			// Used by SmoothScrollToPosition to know when the view 
-			// for the targeted adapterPosition has been attached.
-
-			AndroidView view;
-			if (!_viewByAdaptorPosition.TryGetValue(adapterPosition, out view))
-				return null;
-			return view;
-		}
-
-		public override void ScrollToPosition(int adapterPosition)
-		{
-			if (adapterPosition < 0 || adapterPosition >= ItemCount)
-				throw new ArgumentException(nameof(adapterPosition));
-
-			_scroller.TargetPosition = adapterPosition;
-			StartSmoothScroll(_scroller);
-		}
-		public override void SmoothScrollToPosition(RecyclerView recyclerView, State state, int adapterPosition)
-		{
-			ScrollToPosition(adapterPosition);
-		}
-		public override bool CanScrollHorizontally() => _virtualLayout.CanScrollHorizontally;
-		public override bool CanScrollVertically() => _virtualLayout.CanScrollVertically;
-
-		// entry points
-		public override bool SupportsPredictiveItemAnimations() => true;
-		public override void OnLayoutChildren(Recycler recycler, State state)
-		{
-			var adapterChangeType = _adapterChangeType;
-			if (state.IsPreLayout)
-				adapterChangeType = default(AdapterChangeType);
-
-			// adapter updates
-			if (!state.IsPreLayout)
-			{
-				while (_deferredLayout.Count > 0)
-					_deferredLayout.Dequeue()(recycler, state);
-			}
-
-			// get visible items
-			var positions = _virtualLayout.GetPositions(
-				positionOrigin: _positionOrigin,
-				itemCount: state.ItemCount,
-				viewport: Viewport,
-				// IsPreLayout => some type of data update of yet unknown type. Must assume update 
-				// could be remove so virtualLayout must +1 off-screen left in case origin is 
-				// removed and +n off-screen right to slide onscreen if a big item is removed
-				isPreLayout: state.IsPreLayout || adapterChangeType == AdapterChangeType.Removed
-			).ToRange();
-
-			// disappearing
-			var disappearing = _viewByAdaptorPosition.Keys.Except(positions).ToList();
-
-			// defer cleanup of displaced items and lay them out off-screen so they animate off-screen
-			if (adapterChangeType == AdapterChangeType.Added)
-			{
-				positions = positions.Concat(disappearing).OrderBy(o => o).ToArray();
-				disappearing.Clear();
-			}
-
-			// recycle
-			foreach (var position in disappearing)
-			{
-				var view = _viewByAdaptorPosition[position];
-
-				// remove
-				_viewByAdaptorPosition.Remove(position);
-				OnAppearingOrDisappearing(position, false);
-
-				// scrap
-				new DecoratedView(this, view).DetachAndScrap(recycler);
-			}
-
-			// TODO: Generalize
-			if (adapterChangeType == AdapterChangeType.Removed && _positionOrigin == state.ItemCount - 1)
-			{
-				var vlayout = _virtualLayout.LayoutItem(_positionOrigin, _positionOrigin);
-				_locationOffset = new IntVector(vlayout.Width - Width, _locationOffset.Y);
-			}
-
-			var nextLocationOffset = new IntPoint(int.MaxValue, int.MaxValue);
-			var nextPositionOrigin = int.MaxValue;
-			foreach (var position in positions)
-			{
-				// attach
-				AndroidView view;
-				if (!_viewByAdaptorPosition.TryGetValue(position, out view))
-					AddView(_viewByAdaptorPosition[position] = view = recycler.GetViewForPosition(position));
-
-				// layout
-				var decoratedView = new DecoratedView(this, view);
-				var layout = _virtualLayout.LayoutItem(_positionOrigin, position);
-				var physicalLayout = layout - _locationOffset;
-				decoratedView.Layout(physicalLayout);
-
-				var isVisible = Viewport.IntersectsWith(layout);
-				if (isVisible)
-					OnAppearingOrDisappearing(position, true);
-
-				// update offsets
-				if (isVisible && position < nextPositionOrigin)
-				{
-					nextLocationOffset = layout.Location;
-					nextPositionOrigin = position;
-				}
-			}
-
-			// update origin
-			if (nextPositionOrigin != int.MaxValue)
-			{
-				_positionOrigin = nextPositionOrigin;
-				_locationOffset -= (IntVector)nextLocationOffset;
-			}
-
-			// scrapped views not re-attached must be recycled (why isn't this done by Android, I dunno)
-			foreach (var viewHolder in recycler.ScrapList.ToArray())
-				recycler.RecycleView(viewHolder.ItemView);
-		}
-
-		public override int ScrollHorizontallyBy(int dx, Recycler recycler, State state)
-		{
-			var delta = new IntVector(dx, 0);
-			ScrollBy(ref delta, recycler, state);
-			return delta.X;
-		}
-		public override int ScrollVerticallyBy(int dy, Recycler recycler, State state)
-		{
-			var delta = new IntVector(0, dy);
-			ScrollBy(ref delta, recycler, state);
-			return delta.Y;
-		}
-
-		public override string ToString()
-		{
-			return $"offset={_locationOffset}";
-		}
-	}
-
-	internal class ItemViewAdapter : Adapter
-	{
-		#region Private Definitions
-		class CarouselViewHolder : ViewHolder
-		{
-			#region Fields
-			readonly View _view;
-			readonly IVisualElementRenderer _visualElementRenderer;
-			#endregion
-
-			public CarouselViewHolder(View view, IVisualElementRenderer renderer)
-				: base(renderer.ViewGroup)
-			{
-				_visualElementRenderer = renderer;
-				_view = view;
-			}
-
-			public View View => _view;
-			public IVisualElementRenderer VisualElementRenderer => _visualElementRenderer;
-		}
-		#endregion
-
-		#region Fields
-		readonly IVisualElementRenderer _renderer;
-		readonly Dictionary<int, object> _typeByTypeId;
-		readonly Dictionary<object, int> _typeIdByType;
-		int _nextItemTypeId;
-		#endregion
-
-		public ItemViewAdapter(IVisualElementRenderer carouselRenderer)
-		{
-			_renderer = carouselRenderer;
-			_typeByTypeId = new Dictionary<int, object>();
-			_typeIdByType = new Dictionary<object, int>();
-			_nextItemTypeId = 0;
-		}
-
-		#region Private Members
-		ItemsView Element
-		{
-			get
-			{
-				return (ItemsView)_renderer.Element;
-			}
-		}
-		IItemViewController Controller
-		{
-			get
-			{
-				return Element;
-			}
-		}
-		#endregion
-
-		public override int ItemCount
-		{
-			get
-			{
-				return Controller.Count;
-			}
-		}
-		public override int GetItemViewType(int position)
-		{
-			// get item and type from ItemSource and ItemTemplate
-			object item = Controller.GetItem(position);
-			object type = Controller.GetItemType(item);
-
-			// map type as DataTemplate to type as Id
-			int id = default(int);
-			if (!_typeIdByType.TryGetValue(type, out id))
-			{
-				id = _nextItemTypeId++;
-				_typeByTypeId[id] = type;
-				_typeIdByType[type] = id;
-			}
-			return id;
-		}
-		public override ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
-		{
-			// create view from type
-			var type = _typeByTypeId[viewType];
-			var view = Controller.CreateView(type);
-
-			// create renderer for view
-			var renderer = Platform.CreateRenderer(view);
-			Platform.SetRenderer(view, renderer);
-
-			// package renderer + view
-			return new CarouselViewHolder(view, renderer);
-		}
-		public override void OnBindViewHolder(ViewHolder holder, int position)
-		{
-			var carouselHolder = (CarouselViewHolder)holder;
-
-			var item = Controller.GetItem(position);
-			Controller.BindView(carouselHolder.View, item);
-		}
-	}
-}
\ No newline at end of file