From ac936ce13024e2d0b2ff98e7164e89e7284fe804 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Sun, 21 May 2023 14:56:00 +0200
Subject: [PATCH 1/2] Added failing test for #11290.

---
 .../Input/KeyboardNavigationTests_Tab.cs      | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tests/Avalonia.Base.UnitTests/Input/KeyboardNavigationTests_Tab.cs b/tests/Avalonia.Base.UnitTests/Input/KeyboardNavigationTests_Tab.cs
index 34a9947d28..0b3d1a275b 100644
--- a/tests/Avalonia.Base.UnitTests/Input/KeyboardNavigationTests_Tab.cs
+++ b/tests/Avalonia.Base.UnitTests/Input/KeyboardNavigationTests_Tab.cs
@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using Avalonia.Controls;
 using Avalonia.Input;
+using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Base.UnitTests.Input
@@ -1253,5 +1254,24 @@ namespace Avalonia.Base.UnitTests.Input
 
             Assert.Same(expected, result);
         }
+
+        [Fact]
+        public void Focuses_First_Child_From_No_Focus()
+        {
+            using var app = UnitTestApplication.Start(TestServices.RealFocus);
+            var button = new Button();
+            var root = new TestRoot(button);
+            var target = new KeyboardNavigationHandler();
+
+            target.SetOwner(root);
+
+            root.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Tab,
+            });
+
+            Assert.True(button.IsFocused);
+        }
     }
 }

From 94b9c36e31a63959f7f83e6806d0db8c5da6b6ff Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Sun, 21 May 2023 14:57:01 +0200
Subject: [PATCH 2/2] Focus first child from no focus.

If there is no currently focused element when tab navigation occurs, move the focus from the root.

Fixes #11290.
---
 .../Input/KeyboardNavigationHandler.cs             | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/Avalonia.Base/Input/KeyboardNavigationHandler.cs b/src/Avalonia.Base/Input/KeyboardNavigationHandler.cs
index 7b6da62e2d..7a83501ce4 100644
--- a/src/Avalonia.Base/Input/KeyboardNavigationHandler.cs
+++ b/src/Avalonia.Base/Input/KeyboardNavigationHandler.cs
@@ -77,13 +77,16 @@ namespace Avalonia.Input
         /// <param name="direction">The direction to move.</param>
         /// <param name="keyModifiers">Any key modifiers active at the time of focus.</param>
         public void Move(
-            IInputElement element,
+            IInputElement? element,
             NavigationDirection direction,
             KeyModifiers keyModifiers = KeyModifiers.None)
         {
-            element = element ?? throw new ArgumentNullException(nameof(element));
+            if (element is null && _owner is null)
+            {
+                return;
+            }
 
-            var next = GetNext(element, direction);
+            var next = GetNext(element ?? _owner!, direction);
 
             if (next != null)
             {
@@ -101,10 +104,9 @@ namespace Avalonia.Input
         /// <param name="e">The event args.</param>
         protected virtual void OnKeyDown(object? sender, KeyEventArgs e)
         {
-            var current = FocusManager.GetFocusManager(e.Source as IInputElement)?.GetFocusedElement();
-
-            if (current != null && e.Key == Key.Tab)
+            if (e.Key == Key.Tab)
             {
+                var current = FocusManager.GetFocusManager(e.Source as IInputElement)?.GetFocusedElement();
                 var direction = (e.KeyModifiers & KeyModifiers.Shift) == 0 ?
                     NavigationDirection.Next : NavigationDirection.Previous;
                 Move(current, direction, e.KeyModifiers);