Added Section indexes when FastScrolled is enabled (#850)

* Added Section indexes when FastScrolled is enabled

* Moved the GroupListAdapater to its own file

* Renamed Setup to ValidateSectionData

4 files changed, 92 insertions, 7 deletions

diff --git a/Xamarin.Forms.Platform.Android/Renderers/GroupedListViewAdapter.cs b/Xamarin.Forms.Platform.Android/Renderers/GroupedListViewAdapter.cs
new file mode 100644
index 00000000..313ded24
--- /dev/null
+++ b/Xamarin.Forms.Platform.Android/Renderers/GroupedListViewAdapter.cs
@@ -0,0 +1,82 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Android.Content;
+using Android.Widget;
+using AListView = Android.Widget.ListView;
+
+namespace Xamarin.Forms.Platform.Android
+{
+
+	internal class GroupedListViewAdapter : ListViewAdapter, ISectionIndexer
+	{
+		class SectionData
+		{
+			public int Index { get; set; }
+			public int Length { get; set; }
+			public int Start { get; set; }
+			public int End => Start + Length;
+		}
+		public GroupedListViewAdapter(Context context, AListView realListView, ListView listView) : base(context, realListView, listView)
+		{
+
+		}
+		bool sectionDataValid = false;
+
+		SectionData[] Sections;
+		Java.Lang.Object[] nativeSections;
+		public int GetPositionForSection(int sectionIndex)
+		{
+			ValidateSectionData();
+			return Sections[sectionIndex].Start;
+		}
+
+		public int GetSectionForPosition(int position)
+		{
+			ValidateSectionData();
+			foreach (var section in Sections)
+			{
+				if (section.Start >= position && section.End <= position)
+					return section.Index;
+			}
+			return 0;
+		}
+
+		public Java.Lang.Object[] GetSections()
+		{
+			ValidateSectionData();
+			return nativeSections;
+		}
+
+		void ValidateSectionData()
+		{
+			if (sectionDataValid)
+				return;
+
+			var templatedItems = TemplatedItemsView.TemplatedItems;
+			int count = 0;
+
+			var sectionData = new List<SectionData>();
+			for (var i = 0; i < templatedItems.Count; i++)
+			{
+				var groupCount = templatedItems.GetGroup(i).Count;
+				sectionData.Add(new SectionData { Index = i, Length = groupCount, Start = count });
+				count += groupCount;
+			}
+			Sections = sectionData.ToArray();
+
+			var shortNames = templatedItems.ShortNames;
+			if (shortNames != null)
+			{
+				nativeSections = shortNames.Select(x => new Java.Lang.String(x)).ToArray();
+			}
+			sectionDataValid = true;
+		}
+
+		protected override void InvalidateCount()
+		{
+			base.InvalidateCount();
+			sectionDataValid = false;
+		}
+	}
+}
diff --git a/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs b/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
index 5c23fd2e..4c9d2311 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
@@ -12,7 +12,7 @@ using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms.Platform.Android
 {
-	internal sealed class ListViewAdapter : CellAdapter
+	internal class ListViewAdapter : CellAdapter
 	{
 		const int DefaultGroupHeaderTemplateId = 0;
 		const int DefaultItemTemplateId = 1;
@@ -22,7 +22,7 @@ namespace Xamarin.Forms.Platform.Android
 		internal static readonly BindableProperty IsSelectedProperty = BindableProperty.CreateAttached("IsSelected", typeof(bool), typeof(Cell), false);
 
 		readonly Context _context;
-		readonly ListView _listView;
+		protected readonly ListView _listView;
 		readonly AListView _realListView;
 		readonly Dictionary<DataTemplate, int> _templateToId = new Dictionary<DataTemplate, int>();
 		int _dataTemplateIncrementer = 2; // lets start at not 0 because
@@ -34,7 +34,7 @@ namespace Xamarin.Forms.Platform.Android
 		WeakReference<Cell> _selectedCell;
 
 		IListViewController Controller => _listView;
-		ITemplatedItemsView<Cell> TemplatedItemsView => _listView;
+		protected ITemplatedItemsView<Cell> TemplatedItemsView => _listView;
 
 		public ListViewAdapter(Context context, AListView realListView, ListView listView) : base(context)
 		{
@@ -595,9 +595,10 @@ namespace Xamarin.Forms.Platform.Android
 			Header
 		}
 
-		void InvalidateCount()
+		protected virtual void InvalidateCount()
 		{
 			_listCount = -1;
 		}
 	}
+
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Platform.Android/Renderers/ListViewRenderer.cs b/Xamarin.Forms.Platform.Android/Renderers/ListViewRenderer.cs
index bd241c1a..f15b665a 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/ListViewRenderer.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/ListViewRenderer.cs
@@ -141,7 +141,7 @@ namespace Xamarin.Forms.Platform.Android
 				nativeListView.Focusable = false;
 				nativeListView.DescendantFocusability = DescendantFocusability.AfterDescendants;
 				nativeListView.OnFocusChangeListener = this;
-				nativeListView.Adapter = _adapter = new ListViewAdapter(Context, nativeListView, e.NewElement);
+				nativeListView.Adapter = _adapter = e.NewElement.IsGroupingEnabled && e.NewElement.OnThisPlatform ().IsFastScrollEnabled () ? new GroupedListViewAdapter (Context, nativeListView, e.NewElement) : new ListViewAdapter(Context, nativeListView, e.NewElement);
 				_adapter.HeaderView = _headerView;
 				_adapter.FooterView = _footerView;
 				_adapter.IsAttachedToWindow = _isAttached;
@@ -335,8 +335,9 @@ namespace Xamarin.Forms.Platform.Android
 
 		void UpdateFastScrollEnabled()
 		{
-			if (Control != null)
-				Control.FastScrollEnabled = Element.OnThisPlatform().IsFastScrollEnabled();
+			if (Control != null) {
+				Control.FastScrollEnabled = Element.OnThisPlatform ().IsFastScrollEnabled ();
+			}
 		}
 
 		internal class Container : ViewGroup
diff --git a/Xamarin.Forms.Platform.Android/Xamarin.Forms.Platform.Android.csproj b/Xamarin.Forms.Platform.Android/Xamarin.Forms.Platform.Android.csproj
index e57a501d..bf5344ff 100644
--- a/Xamarin.Forms.Platform.Android/Xamarin.Forms.Platform.Android.csproj
+++ b/Xamarin.Forms.Platform.Android/Xamarin.Forms.Platform.Android.csproj
@@ -255,6 +255,7 @@
     <Compile Include="Extensions\NativeBindingExtensions.cs" />
     <Compile Include="NativeValueConverterService.cs" />
     <Compile Include="NativeBindingservice.cs" />
+    <Compile Include="Renderers\GroupedListViewAdapter.cs" />
     <Compile Include="FastRenderers\ImageRenderer.cs" />
     <Compile Include="Extensions\ImageViewExtensions.cs" />
   </ItemGroup>