From b8e3071376fd6a334cc99839e78f5bc1231d61d0 Mon Sep 17 00:00:00 2001
From: Oliver Wong <htw128@live.com>
Date: Fri, 8 May 2026 16:28:09 +0800
Subject: [PATCH] fix: Metronome may get a null AudioSystem.Instance.

---
 Assets/Scripts/OCES/Metronome.cs | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/Assets/Scripts/OCES/Metronome.cs b/Assets/Scripts/OCES/Metronome.cs
index 3c35c9f..f6e3b2d 100644
--- a/Assets/Scripts/OCES/Metronome.cs
+++ b/Assets/Scripts/OCES/Metronome.cs
@@ -9,11 +9,16 @@ namespace OCES
     /// </summary>
     public class Metronome : MonoBehaviour
     {
+        bool m_isRegistered;
+        
         void OnEnable()
         {
-            AudioSystem.Instance.OnBeat += OnBeat;
-            AudioSystem.Instance.OnBar  += OnBar;
-            AudioSystem.Instance.OnGrid += OnGrid;
+            if (AudioSystem.Instance != null) RegisterCallBack(); 
+        }
+
+        void Start()
+        {
+            if (!this.m_isRegistered) RegisterCallBack();
         }
 
         void OnDisable()
@@ -21,6 +26,14 @@ namespace OCES
             AudioSystem.Instance.OnBeat -= OnBeat;
             AudioSystem.Instance.OnBar  -= OnBar;
             AudioSystem.Instance.OnGrid -= OnGrid;
+            this.m_isRegistered = true;
+        }
+
+        void RegisterCallBack()
+        {
+            AudioSystem.Instance.OnBeat += OnBeat;
+            AudioSystem.Instance.OnBar  += OnBar;
+            AudioSystem.Instance.OnGrid += OnGrid;
         }
 
         static void OnBeat(uint containerId)