Move all the header/footer adjustment to IItemsViewSource

Fixes #7121
Fixes #7102

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7102.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.CollectionView)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 7102, "[Bug] CollectionView Header cause delay to adding items.",
+		PlatformAffected.Android)]
+	public class Issue7102 : TestNavigationPage
+	{
+		protected override void Init()
+		{
+#if APP
+			FlagTestHelpers.SetCollectionViewTestFlag();
+
+			PushAsync(new GalleryPages.CollectionViewGalleries.ObservableCodeCollectionViewGallery(grid: false));
+#endif
+		}
+
+#if UITEST
+		[Test]
+		public void HeaderDoesNotBreakIndexes()
+		{
+			RunningApp.WaitForElement("entryInsert");
+			RunningApp.Tap("entryInsert");
+			RunningApp.ClearText();
+			RunningApp.EnterText("1");
+			RunningApp.Tap("Insert");
+
+			// If the bug is still present, then there will be 
+			// two "Item: 0" items instead of the newly inserted item
+			// Or the header will have disappeared
+			RunningApp.WaitForElement("Inserted");
+			RunningApp.WaitForElement("This is the header");
+		}
+#endif
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -25,7 +25,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue7111.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ShellGestures.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ShellBackButtonBehavior.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)ShellInsets.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue7102.cs" />
+     <Compile Include="$(MSBuildThisFileDirectory)ShellInsets.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)CollectionViewGrouping.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue5412.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Helpers\GarbageCollectionHelper.cs" />

Xamarin.Forms.Controls/CoreGallery.cs

@@ -285,7 +285,7 @@ public override string ToString()
 				new GalleryPageFactory(() => new MemoryLeakGallery(), "Memory Leak"),
 				new GalleryPageFactory(() => new Issues.A11yTabIndex(), "Accessibility TabIndex"),
 				new GalleryPageFactory(() => new FontImageSourceGallery(), "Font ImageSource"),
-				new GalleryPageFactory(() => new CollectionViewGallery(), "CollectionView Gallery"),
+				new GalleryPageFactory(() => new CollectionViewGallery(), "_CollectionView Gallery"),
 				new GalleryPageFactory(() => new CollectionViewCoreGalleryPage(), "CollectionView Core Gallery"),
 				new GalleryPageFactory(() => new Issues.PerformanceGallery(), "Performance"),
 				new GalleryPageFactory(() => new EntryReturnTypeGalleryPage(), "Entry ReturnType "),

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/CollectionModifier.cs

@@ -17,10 +17,10 @@ protected CollectionModifier(CollectionView cv, string buttonText)
 				HorizontalOptions = LayoutOptions.Fill
 			};
 
-			var button = new Button { Text = buttonText, AutomationId = $"btn{buttonText}" };
-			var label = new Label { Text = LabelText, VerticalTextAlignment = TextAlignment.Center };
+			var button = new Button { Text = buttonText, AutomationId = $"btn{buttonText}", HeightRequest = 20, FontSize = 10 };
+			var label = new Label { Text = LabelText, VerticalTextAlignment = TextAlignment.Center, FontSize = 10 };
 
-			Entry = new Entry { Keyboard = Keyboard.Numeric, Text = InitialEntryText, WidthRequest = 100, AutomationId = $"entry{buttonText}" };
+			Entry = new Entry { Keyboard = Keyboard.Numeric, Text = InitialEntryText, WidthRequest = 100, FontSize = 10, AutomationId = $"entry{buttonText}" };
 
 			layout.Children.Add(label);
 			layout.Children.Add(Entry);

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/HeaderFooterGalleries/FooterOnlyString.xaml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             mc:Ignorable="d"
+             x:Class="Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.HeaderFooterGalleries.FooterOnlyString">
+  <ContentPage.Content>
+        <CollectionView x:Name="CollectionView" Footer="This is a footer">
+
+        </CollectionView>
+    </ContentPage.Content>
+</ContentPage>

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/HeaderFooterGalleries/FooterOnlyString.xaml.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using Xamarin.Forms;
+using Xamarin.Forms.Xaml;
+
+namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries.HeaderFooterGalleries
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	public partial class FooterOnlyString : ContentPage
+	{
+		readonly DemoFilteredItemSource _demoFilteredItemSource = new DemoFilteredItemSource(20);
+
+		public FooterOnlyString()
+		{
+			InitializeComponent();
+
+			CollectionView.ItemTemplate = ExampleTemplates.PhotoTemplate();
+			CollectionView.ItemsSource = _demoFilteredItemSource.Items;
+		}
+	}
+}

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/HeaderFooterGalleries/HeaderFooterGallery.cs

@@ -20,6 +20,7 @@ public HeaderFooterGallery()
 						GalleryBuilder.NavButton("Header/Footer (Forms View)", () => new HeaderFooterView(), Navigation),
 						GalleryBuilder.NavButton("Header/Footer (Template)", () => new HeaderFooterTemplate(), Navigation),
 						GalleryBuilder.NavButton("Header/Footer (Grid)", () => new HeaderFooterGrid(), Navigation),
+						GalleryBuilder.NavButton("Footer Only (String)", () => new FooterOnlyString(), Navigation),
 					}
 				}
 			};

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/ObservableCodeCollectionViewGallery.cs

@@ -25,7 +25,8 @@ public ObservableCodeCollectionViewGallery(ItemsLayoutOrientation orientation =
 
 			var itemTemplate = ExampleTemplates.PhotoTemplate();
 
-			var collectionView = new CollectionView {ItemsLayout = itemsLayout, ItemTemplate = itemTemplate, AutomationId = "collectionview" };
+			var collectionView = new CollectionView {ItemsLayout = itemsLayout, ItemTemplate = itemTemplate,
+				AutomationId = "collectionview", Header = "This is the header" };
 
 			var generator = new ItemsSourceGenerator(collectionView, initialItems, ItemsSourceType.ObservableCollection);
 

Xamarin.Forms.Controls/Xamarin.Forms.Controls.csproj

@@ -47,6 +47,9 @@
     <EmbeddedResource Update="GalleryPages\BindableLayoutGalleryPage.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Update="GalleryPages\CollectionViewGalleries\HeaderFooterGalleries\FooterOnlyString.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
     <EmbeddedResource Update="GalleryPages\MapGallery.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>

Xamarin.Forms.Platform.Android/CollectionView/EmptySource.cs

@@ -6,11 +6,34 @@ sealed internal class EmptySource : IItemsViewSource
 	{
 		public int Count => 0;
 
+		public bool HasHeader { get; set; }
+		public bool HasFooter { get; set; }
+
 		public object this[int index] => throw new IndexOutOfRangeException("IItemsViewSource is empty");
 
 		public void Dispose()
 		{
-
+
+		}
+
+		public bool IsHeader(int index)
+		{
+			return HasHeader && index == 0;
+		}
+
+		public bool IsFooter(int index)
+		{
+			if (!HasFooter)
+			{
+				return false;
+			}
+
+			if (HasHeader)
+			{
+				return index == 1;
+			}
+
+			return index == 0;
 		}
 	}
 }

Xamarin.Forms.Platform.Android/CollectionView/IItemsViewSource.cs

@@ -6,5 +6,11 @@ internal interface IItemsViewSource : IDisposable
 	{
 		int Count { get; }
 		object this[int index] { get; }
+
+		bool HasHeader { get; set; }
+		bool HasFooter { get; set; }
+
+		bool IsHeader(int index);
+		bool IsFooter(int index);
 	}
 }

Xamarin.Forms.Platform.Android/CollectionView/ItemsViewAdapter.cs

@@ -17,8 +17,6 @@ public class ItemsViewAdapter : RecyclerView.Adapter
 		Size? _size;
 
 		bool _usingItemTemplate = false;
-		int _headerOffset = 0;
-		bool _hasFooter;
 
 		internal ItemsViewAdapter(ItemsView itemsView, Func<View, Context, ItemContentView> createItemContentView = null)
 		{
@@ -27,29 +25,26 @@ internal ItemsViewAdapter(ItemsView itemsView, Func<View, Context, ItemContentVi
 			ItemsView = itemsView ?? throw new ArgumentNullException(nameof(itemsView));
 
 			UpdateUsingItemTemplate();
-			UpdateHeaderOffset();
-			UpdateHasFooter();
 
 			ItemsView.PropertyChanged += ItemsViewPropertyChanged;
 
 			_createItemContentView = createItemContentView;
 			ItemsSource = ItemsSourceFactory.Create(itemsView.ItemsSource, this);
 
+			UpdateHasHeader();
+			UpdateHasFooter();
+
 			if (_createItemContentView == null)
 			{
 				_createItemContentView = (view, context) => new ItemContentView(context);
 			}
 		}
 
-		private void ItemsViewPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs property)
+		protected virtual void ItemsViewPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs property)
 		{
 			if (property.Is(ItemsView.HeaderProperty))
 			{
-				UpdateHeaderOffset();
-			}
-			else if (property.Is(ItemsView.ItemTemplateProperty))
-			{
-				UpdateUsingItemTemplate();
+				UpdateHasHeader();
 			}
 			else if (property.Is(ItemsView.ItemTemplateProperty))
 			{
@@ -93,7 +88,7 @@ public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int positi
 				return;
 			}
 
-			var itemsSourcePosition = position - _headerOffset;
+			var itemsSourcePosition = position;
 
 			switch (holder)
 			{
@@ -147,7 +142,7 @@ public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int
 			return new TemplatedItemViewHolder(itemContentView, ItemsView.ItemTemplate);
 		}
 
-		public override int ItemCount => ItemsSource.Count + _headerOffset + (_hasFooter ? 1 : 0);
+		public override int ItemCount => ItemsSource.Count;
 
 		public override int GetItemViewType(int position)
 		{
@@ -192,7 +187,7 @@ public virtual int GetPositionForItem(object item)
 			{
 				if (ItemsSource[n] == item)
 				{
-					return n + _headerOffset;
+					return n;
 				}
 			}
 
@@ -204,24 +199,24 @@ void UpdateUsingItemTemplate()
 			_usingItemTemplate = ItemsView.ItemTemplate != null;
 		}
 
-		void UpdateHeaderOffset()
+		void UpdateHasHeader()
 		{
-			_headerOffset = ItemsView.Header == null ? 0 : 1;
+			ItemsSource.HasHeader = ItemsView.Header != null;
 		}
 
 		void UpdateHasFooter()
 		{
-			_hasFooter = ItemsView.Footer != null;
+			ItemsSource.HasFooter = ItemsView.Footer != null;
 		}
 
 		bool IsHeader(int position)
 		{
-			return _headerOffset > 0 && position == 0;
+			return ItemsSource.IsHeader(position);
 		}
 
 		bool IsFooter(int position)
 		{
-			return _hasFooter && position > ItemsSource.Count;
+			return ItemsSource.IsFooter(position);
 		}
 
 		RecyclerView.ViewHolder CreateHeaderFooterViewHolder(object content, DataTemplate template, Context context)

Xamarin.Forms.Platform.Android/CollectionView/ListSource.cs

@@ -3,28 +3,61 @@
 
 namespace Xamarin.Forms.Platform.Android
 {
-	sealed class ListSource : List<object>, IItemsViewSource
+	sealed class ListSource : IItemsViewSource
 	{
+		private List<object> _internal;
+
 		public ListSource()
 		{
 		}
 
-		public ListSource(IEnumerable<object> enumerable) : base(enumerable)
+		public ListSource(IEnumerable<object> enumerable) 
 		{
-
+			_internal = new List<object>(enumerable);
 		}
 
 		public ListSource(IEnumerable enumerable)
 		{
 			foreach (object item in enumerable)
 			{
-				Add(item);
+				_internal.Add(item);
 			}
 		}
 
+		public int Count => _internal.Count + (HasHeader ? 1 : 0) + (HasFooter ? 1 : 0);
+		public object this[int index] => _internal[AdjustIndexRequest(index)];
+
+		public bool HasHeader { get; set; }
+		public bool HasFooter { get; set; }
+
 		public void Dispose()
 		{
 
 		}
+
+		public bool IsFooter(int index)
+		{
+			if (!HasFooter)
+			{
+				return false;
+			}
+
+			if (HasHeader)
+			{
+				return index == Count + 1;
+			}
+
+			return index == Count;
+		}
+
+		public bool IsHeader(int index)
+		{
+			return HasHeader && index == 0;
+		}
+
+		int AdjustIndexRequest(int index)
+		{
+			return index - (HasHeader ? 1 : 0);
+		}
 	}
 }