From 117450dbbe625cab8dad96bf7a336a122bcaf339 Mon Sep 17 00:00:00 2001
From: Poker <poker_sang@outlook.com>
Date: Fri, 21 Feb 2025 03:38:05 +0800
Subject: [PATCH] Fix DockPanel index out of range (#18261)

* Update DockPanel.cs

* Update DockPanelTests.cs
---
 src/Avalonia.Controls/DockPanel.cs                |  4 ++--
 .../Avalonia.Controls.UnitTests/DockPanelTests.cs | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls/DockPanel.cs b/src/Avalonia.Controls/DockPanel.cs
index 2bd90a980f..8850ecc9c7 100644
--- a/src/Avalonia.Controls/DockPanel.cs
+++ b/src/Avalonia.Controls/DockPanel.cs
@@ -179,7 +179,7 @@ namespace Avalonia.Controls
                 }
             }
 
-            if (LastChildFill)
+            if (LastChildFill && Children.Count > 0)
             {
                 var child = Children[Children.Count - 1];
                 var childConstraint = new Size(
@@ -265,7 +265,7 @@ namespace Avalonia.Controls
                 }
             }
 
-            if (LastChildFill)
+            if (LastChildFill && Children.Count > 0)
             {
                 var child = Children[Children.Count - 1];
                 child.Arrange(new Rect(currentBounds.X, currentBounds.Y, currentBounds.Width, currentBounds.Height));
diff --git a/tests/Avalonia.Controls.UnitTests/DockPanelTests.cs b/tests/Avalonia.Controls.UnitTests/DockPanelTests.cs
index d00ef70cde..f88772af76 100644
--- a/tests/Avalonia.Controls.UnitTests/DockPanelTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/DockPanelTests.cs
@@ -4,6 +4,21 @@ namespace Avalonia.Controls.UnitTests
 {
     public class DockPanelTests
     {
+        [Fact]
+        public void DockPanel_Without_Child()
+        {
+            var target = new DockPanel
+            {
+                Width = 10,
+                Height = 10
+            };
+
+            target.Measure(Size.Infinity);
+            target.Arrange(new Rect(target.DesiredSize));
+
+            Assert.Equal(new Rect(0, 0, 10, 10), target.Bounds);
+        }
+        
         [Fact]
         public void Should_Dock_Controls_Horizontal_First()
         {