From 1c01de002b58bd2249f66fcb5738de7dacb4ee45 Mon Sep 17 00:00:00 2001
From: xiaoy312 <xiaoyao312@gmail.com>
Date: Thu, 16 Jan 2025 19:01:25 -0500
Subject: [PATCH] fix: align DepObjCol indexer behavior with winui

(cherry picked from commit 3268696bb277457bab67cea222a9e551a447b3eb)
---
 .../Given_DependencyObjectCollection.cs           | 15 ++++++++++++++-
 src/Uno.UI/UI/Xaml/DependencyObjectCollection.cs  |  2 +-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_DependencyObjectCollection.cs b/src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_DependencyObjectCollection.cs
index 2ea54933aa30..1814b458e3f5 100644
--- a/src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_DependencyObjectCollection.cs
+++ b/src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_DependencyObjectCollection.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices.ObjectiveC;
 using Microsoft.UI.Xaml;
@@ -28,4 +29,16 @@ public void When_Add_Multiple_And_Invoke()
 
 		Assert.IsTrue(list.SequenceEqual(["One", "Two"]));
 	}
+
+	[TestMethod]
+	public void When_Indexer_Get_IndexOutOfRange()
+	{
+		Assert.IsNull(new DependencyObjectCollection()[int.MaxValue]);
+	}
+
+	[TestMethod]
+	public void When_Indexer_Get_NegativeIndex()
+	{
+		Assert.ThrowsException<ArgumentOutOfRangeException>(() => new DependencyObjectCollection()[-1]);
+	}
 }
diff --git a/src/Uno.UI/UI/Xaml/DependencyObjectCollection.cs b/src/Uno.UI/UI/Xaml/DependencyObjectCollection.cs
index 976cef393567..8bd44c87f500 100644
--- a/src/Uno.UI/UI/Xaml/DependencyObjectCollection.cs
+++ b/src/Uno.UI/UI/Xaml/DependencyObjectCollection.cs
@@ -127,7 +127,7 @@ private protected virtual void ValidateItem(T item) { }
 
 		public T this[int index]
 		{
-			get => _list[index];
+			get => index < _list.Count ? _list[index] : default;
 			set
 			{
 				ValidateItem(value);