From ea94d81609799a2af7189033ddd9da80fcd059fb Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Tue, 28 Apr 2026 03:17:02 -0700
Subject: [PATCH] Throw ObjectDisposedException when PlatformImpl is null in
 HeadlessExtension (#21276)

---
 .../Avalonia.Headless/HeadlessWindowExtensions.cs         | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/Headless/Avalonia.Headless/HeadlessWindowExtensions.cs b/src/Headless/Avalonia.Headless/HeadlessWindowExtensions.cs
index 78b89d6cb1..8bb3bf4f34 100644
--- a/src/Headless/Avalonia.Headless/HeadlessWindowExtensions.cs
+++ b/src/Headless/Avalonia.Headless/HeadlessWindowExtensions.cs
@@ -153,7 +153,11 @@ public static class HeadlessWindowExtensions
 
     private static IHeadlessWindow GetImpl(this TopLevel topLevel)
     {
-        return topLevel.PlatformImpl as IHeadlessWindow ??
-               throw new InvalidOperationException("TopLevel must be a headless window.");
+        return topLevel.PlatformImpl switch
+        {
+            null => throw new ObjectDisposedException(topLevel.GetType().Name),
+            IHeadlessWindow headless => headless,
+            _ => throw new InvalidOperationException("TopLevel must be a headless window.")
+        };
     }
 }