更新

WPFDark/Internals/ItemsControlExtensions.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Windows.Controls;
+
+namespace WPFDark.Internals
+{
+    public static class ItemsControlExtensions
+    {
+        internal static IEnumerable<T> EnumerateChildren<T>(this ItemsControl self)
+            where T : ItemsControl
+        {
+            if (self is null)
+                throw new ArgumentNullException(nameof(self));
+
+            for (var i = 0; i < self.Items.Count; i++)
+            {
+                if (!(self.ItemContainerGenerator.ContainerFromIndex(i) is T item))
+                    continue;
+
+                yield return item;
+
+                foreach (var c in item.EnumerateChildren<T>())
+                    yield return c;
+            }
+        }       
+    }
+}