/BaconographyWP8Core/Common/FixedLongListSelector.cs

using BaconographyPortable.Messages;
using BaconographyPortable.ViewModel;
using BaconographyWP8Core.Common;
using GalaSoft.MvvmLight.Messaging;
using Microsoft.Phone.Controls;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Input;
using System.Windows.Media;

namespace BaconographyWP8.Common
{
	public class FixedLongListSelector : Microsoft.Phone.Controls.LongListSelector
	{
		bool viewportChanged = false;
		bool isMoving = false;
		double manipulationStart = 0;
		double manipulationEnd = 0;
        private Dictionary<object, ContentPresenter> items = new Dictionary<object, ContentPresenter>();
		public FixedLongListSelector()
		{
			SelectionChanged += FixedLongListSelector_SelectionChanged;
			ManipulationStateChanged += listbox_ManipulationStateChanged;
			MouseMove += listbox_MouseMove;
			Tap += FixedLongListSelector_Tap;
            ItemRealized += OnItemRealized;
            ItemUnrealized += OnItemUnRealized;
			Compression += FixedLongListSelector_Compression;
		}

		void FixedLongListSelector_Compression(object sender, CompressionEventArgs e)
		{
			if (e.Type == CompressionType.Top)
				PulledDown = true;
			else
				PulledDown = false;
		}

		void FixedLongListSelector_SelectionChanged(object sender, SelectionChangedEventArgs e)
		{
			SelectedItem = base.SelectedItem;
		}

		public static readonly DependencyProperty SelectedItemProperty =
			DependencyProperty.Register(
				"SelectedItem",
				typeof(object),
				typeof(FixedLongListSelector),
				new PropertyMetadata(null, OnSelectedItemChanged)
			);

		public static readonly DependencyProperty PulledDownProperty =
		   DependencyProperty.Register(
			   "PulledDown",
			   typeof(bool),
			   typeof(FixedLongListSelector),
			   new PropertyMetadata(false, OnPulledDownChanged)
		   );

		private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
		{
			var selector = (FixedLongListSelector)d;
			selector.SelectedItem = e.NewValue;
		}

		public new object SelectedItem
		{
			get { return GetValue(SelectedItemProperty); }
			set { SetValue(SelectedItemProperty, value); }
		}

		private static void OnPulledDownChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
		{
			var selector = (FixedLongListSelector)d;
			selector.PulledDown = (bool)e.NewValue;
		}

		public bool PulledDown
		{
			get { return (bool)GetValue(PulledDownProperty); }
			set { SetValue(PulledDownProperty, value); }
		}

		void OnItemRealized(object sender, Microsoft.Phone.Controls.ItemRealizationEventArgs e)
		{
			viewportChanged = true;

            if (e.ItemKind == LongListSelectorItemKind.Item)
            {
                object o = e.Container.DataContext;
                items[o] = e.Container;
            }
		}

        void OnItemUnRealized(object sender, Microsoft.Phone.Controls.ItemRealizationEventArgs e)
        {
            viewportChanged = true;

            if (e.ItemKind == LongListSelectorItemKind.Item)
            {
                object o = e.Container.DataContext;
                items.Remove(o);
            }
        }

		void FixedLongListSelector_Tap(object sender, System.Windows.Input.GestureEventArgs e)
		{
			var pos = e.GetPosition(null);

            var orientationManager = Styles.Resources["orientationManager"] as OrientationManager;
			var val = pos.Y;
			if (orientationManager != null
				&& (orientationManager.Orientation == PageOrientation.Landscape
				|| orientationManager.Orientation == PageOrientation.LandscapeLeft
				|| orientationManager.Orientation == PageOrientation.LandscapeRight))
				val = pos.X;

			if (!isMoving)
				manipulationStart = val;
			else
				manipulationEnd = val;

			isMoving = true;
		}

        OrientationManager _orientationManager;
		void listbox_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
		{
			var pos = e.GetPosition(null);

            var orientationManager = _orientationManager == null ? (_orientationManager = Styles.Resources["orientationManager"] as OrientationManager) : _orientationManager;
			var val = pos.Y;
			if (orientationManager != null
				&& (orientationManager.Orientation == PageOrientation.Landscape
				|| orientationManager.Orientation == PageOrientation.LandscapeLeft
				|| orientationManager.Orientation == PageOrientation.LandscapeRight))
				val = pos.X;

			if (!isMoving)
			{
				manipulationStart = val;
			}
			else
			{
				manipulationEnd = val;
				if (ManipulationState == System.Windows.Controls.Primitives.ManipulationState.Manipulating)
				{
					DoInterimManipulation();
				}
			}

			isMoving = true;
		}

		const int pullDownOffset = 95;
		void DoInterimManipulation()
		{
			var total = manipulationStart - manipulationEnd;
			var viewport = FindViewport(this);
			if (viewport != null)
			{
                var firstVisibleItem = GetFirstVisibleItem();
                if (firstVisibleItem != null && ItemsSource.Count > 0 && firstVisibleItem == ItemsSource[0])
				{
                    if (Math.Abs(total) > pullDownOffset)
                    {
                        var orientationManager = _orientationManager == null ? (_orientationManager = Styles.Resources["orientationManager"] as OrientationManager) : _orientationManager;
                        var adjustedTotal = -total;
                        if (orientationManager != null)
                        {
                            if(orientationManager.Orientation == PageOrientation.LandscapeLeft)
                            {
                                adjustedTotal = total;
                            }
                        }
                        if(adjustedTotal > pullDownOffset)
                            Compression(this, new CompressionEventArgs(CompressionType.Top));
                        else
                            Compression(this, new CompressionEventArgs(CompressionType.None));
                    }
                    else
                        Compression(this, new CompressionEventArgs(CompressionType.None));
				}
				else
				{
					Compression(this, new CompressionEventArgs(CompressionType.None));
				}
			}
		}

		void listbox_ManipulationStateChanged(object sender, EventArgs e)
		{
			if (ManipulationState == System.Windows.Controls.Primitives.ManipulationState.Idle)
			{
				isMoving = false;
				viewportChanged = false;
			}
			else if (ManipulationState == System.Windows.Controls.Primitives.ManipulationState.Manipulating)
			{
				viewportChanged = false;
				DoInterimManipulation();
			}
			else if (ManipulationState == System.Windows.Controls.Primitives.ManipulationState.Animating)
			{
				if (PulledDown)
				{
					// User released, do refresh
					var redditVM = DataContext as RedditViewModel;
					var message = new RefreshSubredditMessage();
					if (redditVM != null)
					{
						message.Subreddit = redditVM.SelectedSubreddit;
						Messenger.Default.Send<RefreshSubredditMessage>(message);
					}
					Compression(this, new CompressionEventArgs(CompressionType.None));
				}
			}
		}


		public event OnCompression Compression;

		#region LLS Util

		public static ViewportControl FindViewport(DependencyObject parent)
		{
			var childCount = VisualTreeHelper.GetChildrenCount(parent);
			for (var i = 0; i < childCount; i++)
			{
				var elt = VisualTreeHelper.GetChild(parent, i);
				if (elt is ViewportControl) return (ViewportControl)elt;
				var result = FindViewport(elt);
				if (result != null) return result;
			}
			return null;
		}

        public object GetFirstVisibleItem()
        {
            var viewPort = FindViewport(this);
            if (items.Count > 0 && viewPort != null)
            {
                var offset = viewPort.Viewport.Top;
                return items.Where(x => Canvas.GetTop(x.Value) + x.Value.ActualHeight > offset)
                    .OrderBy(x => Canvas.GetTop(x.Value)).First().Key;
            }
            else
                return null;
        }
		#endregion
	}

	public class CompressionEventArgs : EventArgs
	{
		public CompressionType Type { get; protected set; }

		public CompressionEventArgs(CompressionType type)
		{
			Type = type;
		}
	}

	public enum CompressionType { None, Top, Bottom, Left, Right };

	public delegate void OnCompression(object sender, CompressionEventArgs e);
}