From de328b1338a7b947e51cd2bb54c7d2826d3cbe2c Mon Sep 17 00:00:00 2001
From: Chris van de Steeg <chris@chrisvandesteeg.nl>
Date: Thu, 21 Mar 2019 14:24:31 +0100
Subject: [PATCH] Fix BindableLayout's incorrect layout.children.add -> use
 insert (#5582)

* Fix incorrect layout.children.add -> use insert

* Modify unit test to match the problem with this issue

- fixes #5579
---
 .../BindableLayoutTests.cs                         |  8 +--
 Xamarin.Forms.Core/BindableLayout.cs               | 72 +++-------------------
 2 files changed, 14 insertions(+), 66 deletions(-)

diff --git a/Xamarin.Forms.Core.UnitTests/BindableLayoutTests.cs b/Xamarin.Forms.Core.UnitTests/BindableLayoutTests.cs
index e2a6ddc..9a4154e 100644
--- a/Xamarin.Forms.Core.UnitTests/BindableLayoutTests.cs
+++ b/Xamarin.Forms.Core.UnitTests/BindableLayoutTests.cs
@@ -49,10 +49,10 @@ namespace Xamarin.Forms.Core.UnitTests
 				IsPlatformEnabled = true,
 			};
 
-			var itemsSource = new ObservableCollection<int>();
+			var itemsSource = new ObservableCollection<int>() { 0, 1, 2, 3, 4 };
 			BindableLayout.SetItemsSource(layout, itemsSource);
 
-			itemsSource.Insert(0, 1);
+			itemsSource.Insert(2, 5);
 			Assert.IsTrue(IsLayoutWithItemsSource(itemsSource, layout));
 		}
 
@@ -413,8 +413,8 @@ namespace Xamarin.Forms.Core.UnitTests
 				OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));
 				OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, changedItems, 0));
 			}
- 		}     
-      
+		}
+
 		class MyDataTemplateSelectorTest : DataTemplateSelector
 		{
 			readonly Func<object, BindableObject, DataTemplate> _func;
diff --git a/Xamarin.Forms.Core/BindableLayout.cs b/Xamarin.Forms.Core/BindableLayout.cs
index 228071e..6bfe6cf 100644
--- a/Xamarin.Forms.Core/BindableLayout.cs
+++ b/Xamarin.Forms.Core/BindableLayout.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections;
 using System.Collections.Specialized;
+using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms
 {
@@ -175,16 +176,16 @@ namespace Xamarin.Forms
 			int i = 0;
 			foreach (object item in _itemsSource)
 			{
-				layout.Children.Add(CreateItemView(item, i++, layout));
+				layout.Children.Add(CreateItemView(item, layout));
 			}
 		}
 
-		View CreateItemView(object item, int index, Layout<View> layout)
+		View CreateItemView(object item, Layout<View> layout)
 		{
-			return CreateItemView(item, index, _itemTemplate ?? _itemTemplateSelector?.SelectTemplate(item, layout));
+			return CreateItemView(item, _itemTemplate ?? _itemTemplateSelector?.SelectTemplate(item, layout));
 		}
 
-		View CreateItemView(object item, int index, DataTemplate dataTemplate)
+		View CreateItemView(object item, DataTemplate dataTemplate)
 		{
 			if (dataTemplate != null)
 			{
@@ -206,63 +207,10 @@ namespace Xamarin.Forms
 				return;
 			}
 
-			switch (e.Action)
-			{
-				case NotifyCollectionChangedAction.Add:
-					{
-						if (e.NewStartingIndex == -1)
-							goto case NotifyCollectionChangedAction.Reset;
-						int i = e.NewStartingIndex;
-						foreach (object item in e.NewItems)
-						{
-							layout.Children.Add(CreateItemView(item, i++, layout));
-						}
-					}
-					break;
-				case NotifyCollectionChangedAction.Remove:
-					{
-						if (e.OldStartingIndex == -1)
-							goto case NotifyCollectionChangedAction.Reset;
-						for (int i = 0; i < e.OldItems.Count; i++)
-						{
-							layout.Children.RemoveAt(e.OldStartingIndex);
-						}
-					}
-					break;
-				case NotifyCollectionChangedAction.Replace:
-					{
-						if (e.OldStartingIndex == -1)
-							goto case NotifyCollectionChangedAction.Reset;
-						int i = e.NewStartingIndex;
-						foreach (object item in e.NewItems)
-						{
-							layout.Children[i] = CreateItemView(item, i, layout);
-							++i;
-						}
-					}
-					break;
-				case NotifyCollectionChangedAction.Move:
-					{
-						if (e.OldStartingIndex == -1 || e.NewStartingIndex == -1)
-							goto case NotifyCollectionChangedAction.Reset;
-						for (int i = 0; i < e.NewItems.Count; ++i)
-						{
-							int iFrom = e.OldStartingIndex + i;
-							int iTo = e.NewStartingIndex + i;
-							View fromView = layout.Children[iFrom];
-							View toView = layout.Children[iTo];
-							layout.Children.Remove(fromView);
-							layout.Children.Remove(toView);
-							layout.Children.Insert(iFrom, toView);
-							layout.Children.Insert(iTo, fromView);
-						}
-					}
-					break;
-
-				case NotifyCollectionChangedAction.Reset:
-					layout.Children.Clear();
-					break;
-			}
+			e.Apply(
+				insert: (item, index, _) => layout.Children.Insert(index, CreateItemView(item, layout)),
+				removeAt: (item, index) => layout.Children.RemoveAt(index),
+				reset: CreateChildren);
 		}
 	}
-}
+}
\ No newline at end of file
-- 
2.7.4