ListViewTests.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Input;
using NUnit.Framework;
using Xamarin.Forms.Internals;

namespace Xamarin.Forms.Core.UnitTests
{
	[TestFixture]
	public class ListViewTests : BaseTestFixture
	{
		[TearDown]
		public override void TearDown()
		{
			base.TearDown ();
			Device.PlatformServices = null;
			Device.Info = null;
		}

		[SetUp]
		public override void Setup ()
		{
			base.Setup ();
			Device.PlatformServices = new MockPlatformServices ();
			Device.Info = new TestDeviceInfo ();
		}

		[Test]
		public void TestConstructor ()
		{
			var listView = new ListView ();
			
			Assert.Null (listView.ItemsSource);
			Assert.Null (listView.ItemTemplate);
			Assert.AreEqual (LayoutOptions.FillAndExpand, listView.HorizontalOptions);
			Assert.AreEqual (LayoutOptions.FillAndExpand, listView.VerticalOptions);
		}

		internal class ListItem
		{
			public string Name { get; set; }
			public string Description { get; set; }

			public override string ToString() => Name ?? base.ToString();
		}

		static ListItem[] CreateListItemCollection()
		{
			return new[]
			{
				new ListItem { Name = "Foo", Description = "Bar" },
				new ListItem { Name = "Baz", Description = "Raz" }
			};
		}

		[Test]
		public void TestTemplating ()
		{
			var cellTemplate = new DataTemplate (typeof (TextCell));
			cellTemplate.SetBinding (TextCell.TextProperty, new Binding ("Name"));
			cellTemplate.SetBinding (TextCell.DetailProperty, new Binding ("Description"));

			var listView = new ListView {
				ItemsSource = CreateListItemCollection(),
				ItemTemplate = cellTemplate
			};

			var cell = (Cell)listView.ItemTemplate.CreateContent ();

			var textCell = (TextCell)cell;
			cell.BindingContext = listView.ItemsSource.OfType<ListItem> ().First ();
			
			Assert.AreEqual ("Foo", textCell.Text);
			Assert.AreEqual ("Bar", textCell.Detail);
		}

		[Test]
		public void TemplateNullObject()
		{
			var listView = new ListView {
				ItemsSource = new object[] {
					null
				}
			};

			Cell cell = listView.TemplatedItems[0];

			Assert.That (cell, Is.Not.Null);
			Assert.That (cell, Is.InstanceOf<TextCell>());
			Assert.That (((TextCell) cell).Text, Is.Null);
		}

		[Test]
		public void ItemTemplateIsNullObjectExecutesToString()
		{
			var listView = new ListView
			{
				ItemsSource = CreateListItemCollection()
			};

			Assert.AreEqual(2, listView.TemplatedItems.Count);

			Cell cell = listView.TemplatedItems[0];
			Assert.That(cell, Is.Not.Null);
			Assert.That(cell, Is.InstanceOf<TextCell>());
			Assert.That(((TextCell)cell).Text, Is.EqualTo("Foo"));

			cell = listView.TemplatedItems[1];
			Assert.That(cell, Is.Not.Null);
			Assert.That(cell, Is.InstanceOf<TextCell>());
			Assert.That(((TextCell)cell).Text, Is.EqualTo("Baz"));
		}

		[Test]
		[Description("Setting BindingContext should trickle down to Header and Footer.")]
		public void SettingBindingContextPassesToHeaderAndFooter()
		{
			var bc = new object();
			var header = new BoxView();
			var footer = new BoxView();
			var listView = new ListView
			{
				Header = header,
				Footer = footer,
				BindingContext = bc,
			};

			Assert.That(header.BindingContext, Is.SameAs(bc));
			Assert.That(footer.BindingContext, Is.SameAs(bc));
		}

		[Test]
		[Description("Setting Header and Footer should pass BindingContext.")]
		public void SettingHeaderFooterPassesBindingContext()
		{
			var bc = new object();
			var listView = new ListView
			{
				BindingContext = bc,
			};

			var header = new BoxView();
			var footer = new BoxView();
			listView.Footer = footer;
			listView.Header = header;

			Assert.That(header.BindingContext, Is.SameAs(bc));
			Assert.That(footer.BindingContext, Is.SameAs(bc));
		}

		[Test]
		[Description ("Setting GroupDisplayBinding or GroupHeaderTemplate when the other is set should set the other one to null.")]
		public void SettingGroupHeaderTemplateSetsDisplayBindingToNull()
		{
			var listView = new ListView {
				GroupDisplayBinding = new Binding ("Path")
			};

			listView.GroupHeaderTemplate = new DataTemplate (typeof (TextCell));

			Assert.That (listView.GroupDisplayBinding, Is.Null);
		}

		[Test]
		[Description ("Setting GroupDisplayBinding or GroupHeaderTemplate when the other is set should set the other one to null.")]
		public void SettingGroupDisplayBindingSetsHeaderTemplateToNull()
		{
			var listView = new ListView {
				GroupHeaderTemplate = new DataTemplate (typeof (TextCell))
			};

			listView.GroupDisplayBinding = new Binding ("Path");

			Assert.That (listView.GroupHeaderTemplate, Is.Null);
		}

		[Test]
		[Description ("You should be able to set ItemsSource without having set the other properties first without issue")]
		public void SettingItemsSourceWithoutBindingsOrItemsSource()
		{
			var listView = new ListView {
				IsGroupingEnabled = true
			};

			Assert.That (() => listView.ItemsSource = new[] { new[] { new object() } }, Throws.Nothing);
		}

		[Test]
		public void DefaultGroupHeaderTemplates()
		{
			var items = new[] { new[] { new object() } };

			var listView = new ListView {
				IsGroupingEnabled = true,
				ItemsSource = items
			};

			var til = (TemplatedItemsList<ItemsView<Cell>, Cell>)((IList)listView.TemplatedItems)[0];
			Cell cell = til.HeaderContent;

			Assert.That (cell, Is.Not.Null);
			Assert.That (cell, Is.InstanceOf<TextCell>());
			Assert.That (((TextCell) cell).Text, Is.EqualTo (items[0].ToString()));
		}

		[Test]
		[Description ("Tapping a different item (row) that is equal to the current item selection should still raise ItemSelected")]
		public void NotifyRowTappedDifferentIndex()
		{
			string item = "item";

			var listView = new ListView {
				ItemsSource = new[] {
					item,
					item
				}
			};

			listView.NotifyRowTapped (0);

			bool raised = false;
			listView.ItemSelected += (sender, arg) => raised = true;

			listView.NotifyRowTapped (1);
			Assert.That (raised, Is.True, "ItemSelected was not raised");
		}

		[Test]
		public void DoesNotCrashWhenAddingToSource ()
		{
			var items = new ObservableCollection<string> {
				"Foo",
				"Bar",
				"Baz"
			};

			var listView = new ListView {
				ItemsSource = items,
				ItemTemplate = new DataTemplate(typeof(TextCell))
			};

			Assert.DoesNotThrow (() => items.Add ("Blah"));
		}

		[Test]
		public void DoesNotThrowWhenMovingInSource ()
		{
			var items = new ObservableCollection<string> {
				"Foo",
				"Bar",
				"Baz"
			};

			var listView = new ListView {
				ItemsSource = items,
				ItemTemplate = new DataTemplate (typeof (TextCell))
			};

			Assert.DoesNotThrow (() => items.Move (0, 1));
		}

		[Test]
		[Description ("A cell being tapped from the UI should raise both tapped events, but not change ItemSelected")]
		public void NotifyTappedSameItem()
		{
			int cellTapped = 0;
			int itemTapped = 0;
			int itemSelected = 0;

			var listView = new ListView {
				ItemsSource = new[] { "item" },
				ItemTemplate = new DataTemplate (() => {
					var cell = new TextCell();
					cell.Tapped += (s, e) => {
						cellTapped++;
					};
					return cell;
				})
			};
			
			listView.ItemTapped += (sender, arg) => itemTapped++;
			listView.ItemSelected += (sender, arg) => itemSelected++;

			listView.NotifyRowTapped (0);

			Assert.That (cellTapped, Is.EqualTo (1), "Cell.Tapped was not raised");
			Assert.That (itemTapped, Is.EqualTo (1), "ListView.ItemTapped was not raised");
			Assert.That (itemSelected, Is.EqualTo (1), "ListView.ItemSelected was not raised");

			listView.NotifyRowTapped (0);

			Assert.That (cellTapped, Is.EqualTo (2), "Cell.Tapped was not raised a second time");
			Assert.That (itemTapped, Is.EqualTo (2), "ListView.ItemTapped was not raised a second time");
			Assert.That (itemSelected, Is.EqualTo (1), "ListView.ItemSelected was raised a second time");
		}

		[Test]
		public void ScrollTo()
		{
			var listView = new ListView {
				IsPlatformEnabled = true,
			};

			object item = new object();

			bool requested = false;
			listView.ScrollToRequested += (sender, args) => {
				requested = true;

				Assert.That (args.Item, Is.SameAs (item));
				Assert.That (args.Group, Is.Null);
				Assert.That (args.Position, Is.EqualTo (ScrollToPosition.Center));
				Assert.That (args.ShouldAnimate, Is.EqualTo (true));
			};

			listView.ScrollTo (item, ScrollToPosition.Center, animated: true);
			Assert.That (requested, Is.True);
		}

		[Test]
		public void ScrollToDelayed()
		{
			var listView = new ListView();

			object item = new object();

			bool requested = false;
			listView.ScrollToRequested += (sender, args) => {
				requested = true;

				Assert.That (args.Item, Is.SameAs (item));
				Assert.That (args.Group, Is.Null);
				Assert.That (args.Position, Is.EqualTo (ScrollToPosition.Center));
				Assert.That (args.ShouldAnimate, Is.EqualTo (true));
			};

			listView.ScrollTo (item, ScrollToPosition.Center, animated: true);
			Assert.That (requested, Is.False);

			listView.IsPlatformEnabled = true;

			Assert.That (requested, Is.True);
		}

		[Test]
		public void ScrollToGroup()
		{
			// Fake a renderer so we pass along messages right away
			var listView = new ListView {
				IsPlatformEnabled = true,
				IsGroupingEnabled = true
			};

			object item = new object();
			object group = new object();

			bool requested = false;
			listView.ScrollToRequested += (sender, args) => {
				requested = true;

				Assert.That (args.Item, Is.SameAs (item));
				Assert.That (args.Group, Is.SameAs (group));
				Assert.That (args.Position, Is.EqualTo (ScrollToPosition.Center));
				Assert.That (args.ShouldAnimate, Is.EqualTo (true));
			};

			listView.ScrollTo (item, group, ScrollToPosition.Center, animated: true);
			Assert.That (requested, Is.True);
		}

		[Test]
		public void ScrollToInvalid()
		{
			var listView = new ListView {
				IsPlatformEnabled = true,
			};

			Assert.That (() => listView.ScrollTo (new object(), (ScrollToPosition) 500, true), Throws.ArgumentException);
			Assert.That (() => listView.ScrollTo (new object(), new object(), ScrollToPosition.Start, true), Throws.InvalidOperationException);

			listView.IsGroupingEnabled = true;
			Assert.That (() => listView.ScrollTo (new object(), new object(), (ScrollToPosition) 500, true), Throws.ArgumentException);
		}

		[Test]
		public void GetSizeRequest ()
		{
			var listView = new ListView {
				IsPlatformEnabled = true,
				HasUnevenRows = false,
				RowHeight = 50,
				ItemsSource = Enumerable.Range (0, 20).ToList ()
			};


			var sizeRequest = listView.GetSizeRequest (double.PositiveInfinity, double.PositiveInfinity);
			Assert.AreEqual (40, sizeRequest.Minimum.Width);
			Assert.AreEqual (40, sizeRequest.Minimum.Height);
			Assert.AreEqual (50, sizeRequest.Request.Width);
			Assert.AreEqual (50 * 20, sizeRequest.Request.Height);
		}

		[Test]
		public void GetSizeRequestUneven ()
		{
			var listView = new ListView {
				IsPlatformEnabled = true,
				HasUnevenRows = true,
				RowHeight = 50,
				ItemsSource = Enumerable.Range (0, 20).ToList ()
			};


			var sizeRequest = listView.GetSizeRequest (double.PositiveInfinity, double.PositiveInfinity);
			Assert.AreEqual (40, sizeRequest.Minimum.Width);
			Assert.AreEqual (40, sizeRequest.Minimum.Height);
			Assert.AreEqual (50, sizeRequest.Request.Width);
			Assert.AreEqual (100, sizeRequest.Request.Height);
		}

		public class ListItemValue : IComparable<ListItemValue>
		{
			public string Name { get; private set; }

			public ListItemValue (string name)
			{
				Name = name;
			}

			int IComparable<ListItemValue>.CompareTo (ListItemValue value)
			{
				return Name.CompareTo (value.Name);
			}

			public string Label
			{
				get { return Name[0].ToString (); }
			}
		}

		public class ListItemCollection : ObservableCollection<ListItemValue>
		{
			public string Title { get; private set; }

			public ListItemCollection (string title)
			{
				Title = title;
			}

			public static List<ListItemValue> GetSortedData ()
			{
				var items = ListItems;
				items.Sort ();
				return items;
			}

			// Data used to populate our list.
			static readonly List<ListItemValue> ListItems = new List<ListItemValue> () {
				new ListItemValue ("Babbage"),
				new ListItemValue ("Boole"),
				new ListItemValue ("Berners-Lee"),
				new ListItemValue ("Atanasoff"),
				new ListItemValue ("Allen"),
				new ListItemValue ("Cormack"),
				new ListItemValue ("Cray"),
				new ListItemValue ("Dijkstra"),
				new ListItemValue ("Dix"),
				new ListItemValue ("Dewey"),
				new ListItemValue ("Erdos"),
			};
		}

		public class TestCell : TextCell
		{
			public static int NumberOfCells = 0;

			public TestCell ()
			{
				Interlocked.Increment (ref NumberOfCells);
			}

			~TestCell ()
			{
				Interlocked.Decrement (ref NumberOfCells);
			}
		}

		ObservableCollection<ListItemCollection> SetupList ()
		{
			var allListItemGroups = new ObservableCollection<ListItemCollection> ();

			foreach (var item in ListItemCollection.GetSortedData ()) {
				// Attempt to find any existing groups where theg group title matches the first char of our ListItem's name.
				var listItemGroup = allListItemGroups.FirstOrDefault (g => g.Title == item.Label);

				// If the list group does not exist, we create it.
				if (listItemGroup == null) {
					listItemGroup = new ListItemCollection (item.Label) { item };
					allListItemGroups.Add (listItemGroup);
				} else {
					// If the group does exist, we simply add the demo to the existing group.
					listItemGroup.Add (item);
				}
			}
			return allListItemGroups;
		}

		[Test]
		public void UncollectableHeaderReferences ()
		{
			var list = new ListView {
				IsPlatformEnabled = true,
				ItemTemplate = new DataTemplate (typeof (TextCell)) {
					Bindings = {
						{TextCell.TextProperty, new Binding ("Name")}
					}
				},
				GroupHeaderTemplate = new DataTemplate (typeof (TestCell)) {
					Bindings = {
						{TextCell.TextProperty, new Binding ("Title")}
					}
				},
				IsGroupingEnabled = true,
				ItemsSource = SetupList (),
			};

			Assert.AreEqual (5, TestCell.NumberOfCells);

			var newList1 = SetupList ();
			var newList2 = SetupList ();

			for (var i = 0; i < 400; i++) {
				list.ItemsSource = i % 2 > 0 ? newList1 : newList2;

				// grab a header just so we can be sure its reailized
				var header = list.TemplatedItems.GetGroup (0).HeaderContent;
			}

			GC.Collect ();
			GC.WaitForPendingFinalizers ();

			// use less or equal because mono will keep the last header var alive no matter what
			Assert.True (TestCell.NumberOfCells <= 6);

			var keepAlive = list.ToString ();
		}

		[Test]
		public void CollectionChangedMultipleFires ()
		{
			var source = new ObservableCollection<string> {
				"Foo",
				"Bar"
			};

			var list = new ListView {
				IsPlatformEnabled = true,
				ItemsSource = source,
				ItemTemplate = new DataTemplate (typeof (TextCell))
			};

			int fireCount = 0;
			list.TemplatedItems.CollectionChanged += (sender, args) => {
				fireCount++;
			};

			source.Add ("Baz");

			Assert.AreEqual (1, fireCount);
		}

		[Test]
		public void GroupedCollectionChangedMultipleFires ()
		{
			var source = new ObservableCollection<ObservableCollection <string>> {
				new ObservableCollection<string> {"Foo"},
				new ObservableCollection<string> {"Bar"}
			};

			var list = new ListView {
				IsPlatformEnabled = true,
				IsGroupingEnabled = true,
				ItemsSource = source,
				ItemTemplate = new DataTemplate (typeof (TextCell)) {
					Bindings = {
						{TextCell.TextProperty, new Binding (".") }
					}
				}
			};

			int fireCount = 0;
			list.TemplatedItems.GroupedCollectionChanged += (sender, args) => {
				fireCount++;
			};

			source[0].Add ("Baz");

			Assert.AreEqual (1, fireCount);
		}

		[Test]
		public void HeaderAsView()
		{
			var label = new Label { Text = "header" };
			var lv = new ListView {
				Header = label
			};

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.SameAs (label));
		}

		[Test]
		public void HeaderTemplated()
		{
			var lv = new ListView {
				Header = "header",
				HeaderTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Not.Null);
			Assert.That (controller.HeaderElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.HeaderElement).Text, Is.EqualTo (lv.Header));
		}

		[Test]
		public void HeaderTemplateThrowsIfCell ()
		{
			var lv = new ListView ();

			Assert.Throws<ArgumentException> (() => lv.HeaderTemplate = new DataTemplate (typeof (TextCell)));
		}

		[Test]
		public void FooterTemplateThrowsIfCell ()
		{
			var lv = new ListView ();

			Assert.Throws<ArgumentException> (() => lv.FooterTemplate = new DataTemplate (typeof (TextCell)));
		}

		[Test]
		public void HeaderObjectTemplatedChanged()
		{
			var lv = new ListView {
				Header = "header",
				HeaderTemplate = new DataTemplate (typeof (Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changed = true;
			};

			lv.Header = "newheader";

			Assert.That (changing, Is.False);
			Assert.That (changed, Is.False);

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Not.Null);
			Assert.That (controller.HeaderElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.HeaderElement).Text, Is.EqualTo (lv.Header));
		}

		[Test]
		public void HeaderViewChanged()
		{
			var lv = new ListView {
				Header = new Label { Text = "header" }
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changed = true;
			};

			Label label = new Label { Text = "header" };
			lv.Header = label;

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.SameAs (label));
		}

		
		[Test]
		public void HeaderTemplateChanged()
		{
			var lv = new ListView {
				Header = "header",
				HeaderTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changed = true;
			};

			lv.HeaderTemplate = new DataTemplate (typeof (Entry)) {
				Bindings = {
					{ Entry.TextProperty, new Binding (".") }
				}
			};

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Not.Null);
			Assert.That (controller.HeaderElement, Is.InstanceOf<Entry>());
			Assert.That (((Entry) controller.HeaderElement).Text, Is.EqualTo (lv.Header));
		}

		[Test]
		public void HeaderTemplateChangedNoObject()
		{
			var lv = new ListView {
				HeaderTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changed = true;
			};

			lv.HeaderTemplate = new DataTemplate (typeof (Entry)) {
				Bindings = {
					{ Entry.TextProperty, new Binding (".") }
				}
			};

			Assert.That (changing, Is.False);
			Assert.That (changed, Is.False);

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Null);
		}

		[Test]
		public void HeaderNoTemplate()
		{
			var lv = new ListView {
				Header = "foo"
			};

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Not.Null);
			Assert.That (controller.HeaderElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.HeaderElement).Text, Is.EqualTo (lv.Header));
		}

		[Test]
		public void HeaderChangedNoTemplate()
		{
			var lv = new ListView {
				Header = "foo"
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changed = true;
			};

			lv.Header = "bar";

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Not.Null);
			Assert.That (controller.HeaderElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.HeaderElement).Text, Is.EqualTo (lv.Header));
		}

		[Test]
		public void HeaderViewButTemplated()
		{
			var lv = new ListView {
				Header = new Entry { Text = "foo" },
				HeaderTemplate = new DataTemplate (typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding ("Text") }
					}
				}
			};

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Not.Null);
			Assert.That (controller.HeaderElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.HeaderElement).Text, Is.EqualTo (((Entry)lv.Header).Text));
		}

		[Test]
		public void HeaderTemplatedChangedToView()
		{
			var lv = new ListView {
				Header = new Entry { Text = "foo" },
				HeaderTemplate = new DataTemplate (typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding ("Text") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changed = true;
			};

			lv.HeaderTemplate = null;

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Not.Null);
			Assert.That (controller.HeaderElement, Is.InstanceOf<Entry>());
			Assert.That (((Entry) controller.HeaderElement).Text, Is.EqualTo (((Entry)lv.Header).Text));
		}

		[Test]
		public void HeaderTemplatedSetToNull()
		{
			var lv = new ListView {
				Header = "header",
				HeaderTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "HeaderElement")
					changed = true;
			};

			lv.Header = null;

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.HeaderElement, Is.Null);
		}

		[Test]
		public void FooterAsView()
		{
			var label = new Label { Text = "footer" };
			var lv = new ListView {
				Footer = label
			};

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.SameAs (label));
		}

		[Test]
		public void FooterTemplated()
		{
			var lv = new ListView {
				Footer = "footer",
				FooterTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Not.Null);
			Assert.That (controller.FooterElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.FooterElement).Text, Is.EqualTo (lv.Footer));
		}

		[Test]
		public void FooterObjectTemplatedChanged()
		{
			var lv = new ListView {
				Footer = "footer",
				FooterTemplate = new DataTemplate (typeof (Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changed = true;
			};

			lv.Footer = "newfooter";

			Assert.That (changing, Is.False);
			Assert.That (changed, Is.False);

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Not.Null);
			Assert.That (controller.FooterElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.FooterElement).Text, Is.EqualTo (lv.Footer));
		}

		[Test]
		public void FooterViewChanged()
		{
			var lv = new ListView {
				Footer = new Label { Text = "footer" }
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changed = true;
			};

			Label label = new Label { Text = "footer" };
			lv.Footer = label;

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.SameAs (label));
		}

		
		[Test]
		public void FooterTemplateChanged()
		{
			var lv = new ListView {
				Footer = "footer",
				FooterTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changed = true;
			};

			lv.FooterTemplate = new DataTemplate (typeof (Entry)) {
				Bindings = {
					{ Entry.TextProperty, new Binding (".") }
				}
			};

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Not.Null);
			Assert.That (controller.FooterElement, Is.InstanceOf<Entry>());
			Assert.That (((Entry) controller.FooterElement).Text, Is.EqualTo (lv.Footer));
		}

		[Test]
		public void FooterTemplateChangedNoObject()
		{
			var lv = new ListView {
				FooterTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changed = true;
			};

			lv.FooterTemplate = new DataTemplate (typeof (Entry)) {
				Bindings = {
					{ Entry.TextProperty, new Binding (".") }
				}
			};

			Assert.That (changing, Is.False);
			Assert.That (changed, Is.False);

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Null);
		}

		[Test]
		public void FooterNoTemplate()
		{
			var lv = new ListView {
				Footer = "foo"
			};

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Not.Null);
			Assert.That (controller.FooterElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.FooterElement).Text, Is.EqualTo (lv.Footer));
		}

		[Test]
		public void FooterChangedNoTemplate()
		{
			var lv = new ListView {
				Footer = "foo"
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changed = true;
			};

			lv.Footer = "bar";

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Not.Null);
			Assert.That (controller.FooterElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.FooterElement).Text, Is.EqualTo (lv.Footer));
		}

		[Test]
		public void FooterViewButTemplated()
		{
			var lv = new ListView {
				Footer = new Entry { Text = "foo" },
				FooterTemplate = new DataTemplate (typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding ("Text") }
					}
				}
			};

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Not.Null);
			Assert.That (controller.FooterElement, Is.InstanceOf<Label>());
			Assert.That (((Label) controller.FooterElement).Text, Is.EqualTo (((Entry)lv.Footer).Text));
		}

		[Test]
		public void FooterTemplatedChangedToView()
		{
			var lv = new ListView {
				Footer = new Entry { Text = "foo" },
				FooterTemplate = new DataTemplate (typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding ("Text") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changed = true;
			};

			lv.FooterTemplate = null;

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Not.Null);
			Assert.That (controller.FooterElement, Is.InstanceOf<Entry>());
			Assert.That (((Entry) controller.FooterElement).Text, Is.EqualTo (((Entry)lv.Footer).Text));
		}

		[Test]
		public void FooterTemplatedSetToNull()
		{
			var lv = new ListView {
				Footer = "footer",
				FooterTemplate = new DataTemplate(typeof(Label)) {
					Bindings = {
						{ Label.TextProperty, new Binding (".") }
					}
				}
			};

			bool changed = false, changing = false;
			lv.PropertyChanging += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changing = true;
			};
			lv.PropertyChanged += (sender, args) => {
				if (args.PropertyName == "FooterElement")
					changed = true;
			};

			lv.Footer = null;

			Assert.That (changing, Is.True);
			Assert.That (changed, Is.True);

			IListViewController controller = lv;
			Assert.That (controller.FooterElement, Is.Null);
		}

		[Test]
		public void BeginRefresh()
		{
			var lv = new ListView();

			bool refreshing = false;
			lv.Refreshing += (sender, args) => {
				refreshing = true;
			};

			lv.BeginRefresh();

			Assert.That (refreshing, Is.True);
			Assert.That (lv.IsRefreshing, Is.True);
		}

		[Test]
		public void SendRefreshing()
		{
			var lv = new ListView();

			bool refreshing = false;
			lv.Refreshing += (sender, args) => {
				refreshing = true;
			};

			IListViewController controller = lv;
			controller.SendRefreshing();

			Assert.That (refreshing, Is.True);
			Assert.That (lv.IsRefreshing, Is.True);
		}

		[Test]
		public void RefreshCommand()
		{
			var lv = new ListView();

			bool commandExecuted = false;

			Command refresh = new Command (() => commandExecuted = true);

			lv.RefreshCommand = refresh;

			IListViewController controller = lv;
			controller.SendRefreshing();

			Assert.That (commandExecuted, Is.True);
		}

		[TestCase (true)]
		[TestCase (false)]
		public void RefreshCommandCanExecute (bool initial)
		{
			var lv = new ListView { IsPullToRefreshEnabled = initial };

			bool commandExecuted = false;

			Command refresh = new Command (() => commandExecuted = true,
				() => !initial);

			lv.RefreshCommand = refresh;

			Assert.That ((lv as IListViewController).RefreshAllowed, Is.EqualTo (!initial));
		}

		[TestCase (true)]
		[TestCase (false)]
		public void RefreshCommandCanExecuteChanges (bool initial)
		{
			var lv = new ListView { IsPullToRefreshEnabled = initial };

			bool commandExecuted = false;

			Command refresh = new Command (() => commandExecuted = true,
				() => initial);

			lv.RefreshCommand = refresh;

			Assert.That ((lv as IListViewController).RefreshAllowed, Is.EqualTo (initial));

			initial = !initial;
			refresh.ChangeCanExecute();

			Assert.That ((lv as IListViewController).RefreshAllowed, Is.EqualTo (initial));
		}

		[Test]
		public void BeginRefreshDoesNothingWhenCannotExecute()
		{
			var lv = new ListView();

			bool commandExecuted = false, eventFired = false;

			lv.Refreshing += (sender, args) => eventFired = true;

			Command refresh = new Command (() => commandExecuted = true,
				() => false);

			lv.RefreshCommand = refresh;
			lv.BeginRefresh();

			Assert.That (lv.IsRefreshing, Is.False);
			Assert.That (eventFired, Is.False);
			Assert.That (commandExecuted, Is.False);
		}

		[Test]
		public void SendRefreshingDoesNothingWhenCannotExecute()
		{
			var lv = new ListView();

			bool commandExecuted = false, eventFired = false;

			lv.Refreshing += (sender, args) => eventFired = true;

			Command refresh = new Command (() => commandExecuted = true,
				() => false);

			lv.RefreshCommand = refresh;
			
			((IListViewController)lv).SendRefreshing();

			Assert.That (lv.IsRefreshing, Is.False);
			Assert.That (eventFired, Is.False);
			Assert.That (commandExecuted, Is.False);
		}

		[Test]
		public void SettingIsRefreshingDoesntFireEvent()
		{
			var lv = new ListView();

			bool refreshing = false;
			lv.Refreshing += (sender, args) => {
				refreshing = true;
			};

			lv.IsRefreshing = true;

			Assert.That (refreshing, Is.False);
		}

		[Test]
		public void EndRefresh()
		{
			var lv = new ListView { IsRefreshing = true };

			Assert.That (lv.IsRefreshing, Is.True);

			lv.EndRefresh();

			Assert.That (lv.IsRefreshing, Is.False);
		}

		[Test]
		public void CanRefreshAfterCantExecuteCommand()
		{
			var lv = new ListView();

			bool commandExecuted = false, eventFired = false;

			lv.Refreshing += (sender, args) => eventFired = true;

			Command refresh = new Command (() => commandExecuted = true,
				() => false);

			lv.RefreshCommand = refresh;
			lv.RefreshCommand = null;

			((IListViewController)lv).SendRefreshing();

			Assert.That (lv.IsRefreshing, Is.True);
			Assert.That (eventFired, Is.True);
			Assert.That (commandExecuted, Is.False);
		}

		[Test]
		public void StopsListeningToCommandAfterCleared()
		{
			var lv = new ListView();

			bool commandExecuted = false, canExecuteRequested = false;

			Command refresh = new Command (() => commandExecuted = true,
				() => canExecuteRequested = true);

			lv.RefreshCommand = refresh;
			canExecuteRequested = false;

			lv.RefreshCommand = null;

			Assert.That (() => refresh.ChangeCanExecute(), Throws.Nothing);
			Assert.That (canExecuteRequested, Is.False);

			lv.BeginRefresh();

			Assert.That (commandExecuted, Is.False);
		}

		[Test]
		[Description ("We should be able to set selected item when using ReadOnlyList")]
		public void SetItemSelectedOnReadOnlyList()
		{
			var source = new ReadOnlySource ();
			var listView = new ListView {
				ItemsSource = source
			};

			bool raised = false;
			listView.ItemSelected += (sender, arg) => raised = true;

			listView.SelectedItem = source [0];
			Assert.That (raised, Is.True, "ItemSelected was raised on ReadOnlySource");
		}

		internal class ReadOnlySource : IReadOnlyList<ListItem>
		{
			List<ListItem> items;
			public ReadOnlySource ()
			{
				items = new List<ListItem> ();

				for (int i = 0; i < 100; i++) {
					items.Add (new ListItem { Name="person " + i } );
				}

			}
			#region IEnumerable implementation
			public IEnumerator<ListItem> GetEnumerator ()
			{
				return items.GetEnumerator ();
			}
			#endregion
			#region IEnumerable implementation
			System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator ()
			{
				return items.GetEnumerator ();
			}
			#endregion
			#region IReadOnlyList implementation
			public ListItem this [int index] {
				get {
					return items [index];
				}
			}
			#endregion
			#region IReadOnlyCollection implementation
			public int Count {
				get {
					return items.Count;
				}
			}
			#endregion

		}

		[Test]
		public void ChildElementsParentIsNulledWhenReset()
		{
			var list = new ListView();
			list.ItemsSource = new[] { "Hi", "Bye" };

			var cell = list.TemplatedItems[0];
			Assume.That (cell.Parent, Is.SameAs (list));

			list.ItemsSource = null;
			Assert.That (cell.Parent, Is.Null);
		}

		[Test]
		public void ChildElementsParentIsNulledWhenRemoved()
		{
			var collection = new ObservableCollection<string> {
				"Hi", "Bye"
			};

			var list = new ListView();
			list.ItemsSource = collection;

			var cell = list.TemplatedItems[0];
			Assume.That (cell.Parent, Is.SameAs (list));

			collection.Remove (collection[0]);
			Assert.That (cell.Parent, Is.Null);
		}

		[Test]
		public void ChildElementsParentIsNulledWhenCleared()
		{
			var collection = new ObservableCollection<string> {
				"Hi", "Bye"
			};

			var list = new ListView();
			list.ItemsSource = collection;

			var cell = list.TemplatedItems[0];
			Assume.That (cell.Parent, Is.SameAs (list));

			collection.Clear();
			Assert.That (cell.Parent, Is.Null);
		}

		[TestCase (Device.Android, ListViewCachingStrategy.RecycleElement)]
		[TestCase (Device.iOS, ListViewCachingStrategy.RecycleElement)]
		[TestCase(Device.UWP, ListViewCachingStrategy.RetainElement)]
		[TestCase ("Other", ListViewCachingStrategy.RetainElement)]
		public void EnforcesCachingStrategy (string platform, ListViewCachingStrategy expected)
		{
			var oldOS = Device.RuntimePlatform;
			// we need to do this because otherwise we cant set the caching strategy
			((MockPlatformServices)Device.PlatformServices).RuntimePlatform = platform;
			var listView = new ListView (ListViewCachingStrategy.RecycleElement);

			Assert.AreEqual (expected, listView.CachingStrategy);
			((MockPlatformServices)Device.PlatformServices).RuntimePlatform = oldOS;
		}

		[Test]
		public void DefaultCacheStrategy ()
		{
			var listView = new ListView ();

			Assert.AreEqual (ListViewCachingStrategy.RetainElement, listView.CachingStrategy);
		}

		[Test]
		public void DoesNotRetainInRecycleMode ()
		{
			var items = new ObservableCollection<string> {
				"Foo",
				"Bar"
			};

			var oldOS = Device.RuntimePlatform;
			// we need to do this because otherwise we cant set the caching strategy
			((MockPlatformServices)Device.PlatformServices).RuntimePlatform = Device.Android;

			var bindable = new ListView (ListViewCachingStrategy.RecycleElement);
			bindable.ItemTemplate = new DataTemplate (typeof (TextCell)) {
				Bindings = {
					{ TextCell.TextProperty, new Binding (".") }
				}
			};

			bindable.ItemsSource = items;
			var item1 = bindable.TemplatedItems[0];
			var item2 = bindable.TemplatedItems[0];

			Assert.False(ReferenceEquals (item1, item2));

			((MockPlatformServices)Device.PlatformServices).RuntimePlatform = oldOS;
		}
	}
}