From e574acd85f831360e97350d7a6a1d57620de684d Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Fri, 18 Sep 2020 09:03:10 +0200
Subject: [PATCH 1/4] Mark TabOnceActiveElement value as nullable.

---
 src/Avalonia.Input/KeyboardNavigation.cs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/Avalonia.Input/KeyboardNavigation.cs b/src/Avalonia.Input/KeyboardNavigation.cs
index 722215f8b7..6ef3c4fd60 100644
--- a/src/Avalonia.Input/KeyboardNavigation.cs
+++ b/src/Avalonia.Input/KeyboardNavigation.cs
@@ -25,12 +25,11 @@ namespace Avalonia.Input
         /// attached property set to <see cref="KeyboardNavigationMode.Once"/>, this property
         /// defines to which child the focus should move.
         /// </remarks>
-        public static readonly AttachedProperty<IInputElement> TabOnceActiveElementProperty =
-            AvaloniaProperty.RegisterAttached<InputElement, IInputElement>(
+        public static readonly AttachedProperty<IInputElement?> TabOnceActiveElementProperty =
+            AvaloniaProperty.RegisterAttached<InputElement, IInputElement?>(
                 "TabOnceActiveElement",
                 typeof(KeyboardNavigation));
 
-
         /// <summary>
         /// Defines the IsTabStop attached property.
         /// </summary>
@@ -68,7 +67,7 @@ namespace Avalonia.Input
         /// </summary>
         /// <param name="element">The container.</param>
         /// <returns>The active element for the container.</returns>
-        public static IInputElement GetTabOnceActiveElement(InputElement element)
+        public static IInputElement? GetTabOnceActiveElement(InputElement element)
         {
             return element.GetValue(TabOnceActiveElementProperty);
         }
@@ -78,7 +77,7 @@ namespace Avalonia.Input
         /// </summary>
         /// <param name="element">The container.</param>
         /// <param name="value">The active element for the container.</param>
-        public static void SetTabOnceActiveElement(InputElement element, IInputElement value)
+        public static void SetTabOnceActiveElement(InputElement element, IInputElement? value)
         {
             element.SetValue(TabOnceActiveElementProperty, value);
         }

From 89684e5b94d51b432a4476d089c1f1a2df8782a6 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Thu, 17 Sep 2020 17:46:07 +0200
Subject: [PATCH 2/4] Short-circuit setting source to current value.

---
 src/Avalonia.Controls/Selection/InternalSelectionModel.cs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/Avalonia.Controls/Selection/InternalSelectionModel.cs b/src/Avalonia.Controls/Selection/InternalSelectionModel.cs
index a28e4b2785..fcdaf44166 100644
--- a/src/Avalonia.Controls/Selection/InternalSelectionModel.cs
+++ b/src/Avalonia.Controls/Selection/InternalSelectionModel.cs
@@ -63,6 +63,11 @@ namespace Avalonia.Controls.Selection
 
         private protected override void SetSource(IEnumerable? value)
         {
+            if (Source == value)
+            {
+                return;
+            }
+
             object?[]? oldSelection = null;
 
             if (Source is object && value is object)

From 544686b78d99674bf50984ce5e97008a8a3d319a Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Fri, 18 Sep 2020 11:41:04 +0200
Subject: [PATCH 3/4] Don't try to SelectAll with single selection.

`Toggle` doesn't mean multiple selection.
---
 src/Avalonia.Controls/Primitives/SelectingItemsControl.cs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs b/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
index c954f9fd4a..e34b3b145f 100644
--- a/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
+++ b/src/Avalonia.Controls/Primitives/SelectingItemsControl.cs
@@ -491,8 +491,7 @@ namespace Avalonia.Controls.Primitives
 
                 if (ItemCount > 0 &&
                     Match(keymap.SelectAll) &&
-                    (((SelectionMode & SelectionMode.Multiple) != 0) ||
-                      (SelectionMode & SelectionMode.Toggle) != 0))
+                    SelectionMode.HasFlag(SelectionMode.Multiple))
                 {
                     Selection.SelectAll();
                     e.Handled = true;

From 08a8badd7afbf87c45d985de815b82b9d64fc6f0 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Fri, 18 Sep 2020 00:28:56 +0200
Subject: [PATCH 4/4] Don't try to realize index -1.

`Algorithm_GetAnchorForTargetElement` can return -1 and when it does so we try to realize that item, which obviously doesn't exist, so boom.
---
 src/Avalonia.Layout/FlowLayoutAlgorithm.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Layout/FlowLayoutAlgorithm.cs b/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
index cd7f725f18..eace54d2e0 100644
--- a/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
+++ b/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
@@ -211,7 +211,7 @@ namespace Avalonia.Layout
                             anchorPosition = new Point(anchorBounds.X, anchorBounds.Y);
                         }
                     }
-                    else
+                    else if (anchorIndex >= 0)
                     {
                         // It is possible to end up in a situation during a collection change where GetAnchorForTargetElement returns an index
                         // which is not in the realized range. Eg. insert one item at index 0 for a grid layout.