From fdd15cd5eca51af229f51c11c867577ee5b6e871 Mon Sep 17 00:00:00 2001
From: Jamie Taylor <me@nekodex.net>
Date: Fri, 29 Nov 2024 06:44:20 +0900
Subject: [PATCH] Add callback for when a submenu is opened

---
 osu.Framework/Graphics/UserInterface/Menu.cs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/osu.Framework/Graphics/UserInterface/Menu.cs b/osu.Framework/Graphics/UserInterface/Menu.cs
index ac178cf5ba..bf7de99ca6 100644
--- a/osu.Framework/Graphics/UserInterface/Menu.cs
+++ b/osu.Framework/Graphics/UserInterface/Menu.cs
@@ -32,6 +32,12 @@ public abstract partial class Menu : CompositeDrawable, IStateful<MenuState>
         [CanBeNull]
         public event Action<MenuState> StateChanged;
 
+        /// <summary>
+        /// Invoked when a Sub-<see cref="Menu"/> is opened.
+        /// </summary>
+        [CanBeNull]
+        public event Action<Menu> OnSubmenuOpen;
+
         /// <summary>
         /// Gets or sets the delay before opening sub-<see cref="Menu"/>s when menu items are hovered.
         /// </summary>
@@ -563,6 +569,8 @@ private void openSubmenuFor(DrawableMenuItem item)
                 submenu.StateChanged += submenuStateChanged;
             }
 
+            bool submenuChanged = submenu.triggeringItem != item;
+
             submenu.triggeringItem = item;
             submenu.positionLayout.Invalidate();
 
@@ -574,6 +582,10 @@ private void openSubmenuFor(DrawableMenuItem item)
                     Schedule(delegate { GetContainingFocusManager().AsNonNull().ChangeFocus(submenu); });
                 else
                     submenu.Open();
+
+                // Check if submenu has changed before firing, to prevent extraneous callbacks (e.g. re-hovering the triggeringItem of an already open submenu)
+                if (submenuChanged)
+                    OnSubmenuOpen?.Invoke(submenu);
             }
             else
                 submenu.Close();