[Android] Support up to 20 templates, as documented. (#929)

* Add repro for 42956

* [Android] Support up to 20 templates, as documented.

* Spaces -> tabs

* A little more info on the _dataTemplateIncrementer

* Fix test case number

1 files changed, 13 insertions, 2 deletions

diff --git a/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs b/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
index 17c7ffa7..b577ec1c 100644
--- a/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
+++ b/Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs
@@ -25,7 +25,12 @@ namespace Xamarin.Forms.Platform.Android
 		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
+		int _dataTemplateIncrementer = 2; // lets start at not 0 because ... 
+
+		// We will use _dataTemplateIncrementer to get the proper ViewType key for the item's DataTemplate and store these keys in  _templateToId.
+		// If an item does _not_ use a DataTemplate, then the ViewType key will be DefaultItemTemplateId (1) or DefaultGroupHeaderTemplateId (0).
+		// To prevent a conflict in the event that a ListView supports both templates and non-templates, we will start the DataTemplate key at 2.
+
 		int _listCount = -1; // -1 we need to get count from the list
 		Cell _enabledCheckCell;
 
@@ -109,7 +114,13 @@ namespace Xamarin.Forms.Platform.Android
 
 		public override int ViewTypeCount
 		{
-			get { return 20; }
+			get
+			{
+				// We have a documented limit of 20 templates on Android.
+				// ViewTypes are selected on a zero-based index, so this count must be at least 20 + 1.
+				// Plus, we arbitrarily increased the index of the DataTemplate index by 2 (see _dataTemplateIncrementer).
+				return 23;
+			}
 		}
 
 		public override bool AreAllItemsEnabled()