From 754bdd4220e91cae5c76466cc98d88c41c761075 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Tue, 22 Aug 2023 13:44:00 +0200
Subject: [PATCH] Handle changing ItemContainerTheme properly.

Previously only handled the case where the `ItemContainerTheme` was changing from null -> non-null.

Fixes #12620
---
 src/Avalonia.Controls/ItemsControl.cs | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/Avalonia.Controls/ItemsControl.cs b/src/Avalonia.Controls/ItemsControl.cs
index 83aa88a7b6..47b943ed2e 100644
--- a/src/Avalonia.Controls/ItemsControl.cs
+++ b/src/Avalonia.Controls/ItemsControl.cs
@@ -665,12 +665,10 @@ namespace Avalonia.Controls
         {
             var itemContainerTheme = ItemContainerTheme;
 
-            if (itemContainerTheme is not null &&
-                !container.IsSet(ThemeProperty) &&
-                StyledElement.GetStyleKey(container) == itemContainerTheme.TargetType)
-            {
+            if (itemContainerTheme is null)
+                container.Theme = null;
+            else if (GetStyleKey(container) == itemContainerTheme.TargetType)
                 container.Theme = itemContainerTheme;
-            }
 
             if (item is not Control)
                 container.DataContext = item;