如何修复QuartzCore中CA::Layer::sublayers()崩溃问题？

部分用户反馈应用出现崩溃，但本地无法复现该故障。以下是从Crashlytics获取的堆栈跟踪信息，据此整理出具体排查方向：

Crashed: com.apple.main-thread
0  QuartzCore                     0x5d340 CA::Layer::sublayers() + 4
1  UIKitCore                      0x40d84 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 116
2  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
3  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
4  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
5  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
6  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
7  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
8  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
9  UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
10 UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
11 UIKitCore                      0x40de8 __88-[UIView(Internal) _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:]_block_invoke + 216
12 UIKitCore                      0x55104 -[UIView _performUpdatesForPossibleChangesOfIdiom:orScreen:traverseHierarchy:] + 216
13 UIKitCore                      0x49120 -[UIView _didChangeFromIdiomOnScreen:traverseHierarchy:] + 112
14 UIKitCore                      0x420578 -[UIWindow _didMoveFromScreen:toScreen:] + 684
15 UIKitCore                      0x2a2c18 -[UIWindow _didMoveFromScene:toScene:] + 296
16 UIKitCore                      0x2a29e0 -[UIWindowScene _attachWindow:] + 140
17 UIKitCore                      0x2a4b34 -[_UIScreenBasedWindowScene _attachWindow:] + 52
18 UIKitCore                      0x343790 -[UIWindow _setWindowHostingScene:] + 196
19 UIKitCore                      0x34368c -[UIWindow setWindowScene:] + 212
20 UIKitCore                      0x69e714 _UIApplicationSceneDisconnectionHandler_block_invoke_3 + 688
21 UIKitCore                      0x4a5c60 -[UIScene _invalidate] + 804
22 UIKitCore                      0x508da0 -[UIWindowScene _invalidate] + 148
23 UIKitCore                      0x47235c -[UIApplication workspace:willDestroyScene:withTransitionContext:completion:] + 180
24 UIKitCore                      0x46053c -[UIApplicationSceneClientAgent scene:willInvalidateWithEvent:completion:] + 288
25 FrontBoardServices             0x1c950 -[FBSScene _callOutQueue_agent_willDestroyWithTransitionContext:completion:] + 236
26 FrontBoardServices             0x20f4c __84-[FBSWorkspaceScenesClient _queue_invalidateScene:withTransitionContext:completion:]_block_invoke_2 + 120
27 FrontBoardServices             0x7120 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:] + 168
28 FrontBoardServices             0x1b5cc __84-[FBSWorkspaceScenesClient _queue_invalidateScene:withTransitionContext:completion:]_block_invoke + 292
29 libdispatch.dylib              0x3eac _dispatch_client_callout + 20
30 libdispatch.dylib              0x791c _dispatch_block_invoke_direct + 264
31 FrontBoardServices             0x1124c __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 52
32 FrontBoardServices             0x10de8 -[FBSSerialQueue _targetQueue_performNextIfPossible] + 220
33 FrontBoardServices             0x13694 -[FBSSerialQueue _performNextFromRunLoopSource] + 28
34 CoreFoundation                 0xd3128 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 28
35 CoreFoundation                 0xdf7b4 __CFRunLoopDoSource0 + 176
36 CoreFoundation                 0x645e8 __CFRunLoopDoSources0 + 244
37 CoreFoundation                 0x7a0d4 __CFRunLoopRun + 828
38 CoreFoundation                 0x7f3ec CFRunLoopRunSpecific + 612
39 GraphicsServices               0x135c GSEventRunModal + 164
40 UIKitCore                      0x39cf58 -[UIApplication _run] + 888
41 UIKitCore                      0x39cbbc UIApplicationMain + 340
42 myApp-ios                     0xae7c main + 24 (AppDelegate.swift:24)
43 ???                            0x1dd91cdec (Missing)

具体排查方向 #

• 检查视图层级中的野指针/已释放对象：崩溃发生在访问CALayer的sublayers时，大概率是某个UIView或CALayer已被释放但仍存在于视图层级中。重点关注场景切换（多窗口、分屏、App前后台切换）时，是否有异步释放UI组件但未从层级中移除的操作。
• 排查自定义视图/图层的内存管理：如果使用了自定义UIView或CALayer，检查dealloc方法是否正确移除子视图/图层，是否存在对象释放后仍被强引用持有的情况，避免内存混乱。
• 模拟场景切换/窗口迁移场景：尝试触发iPad分屏切换、多窗口管理、App后台强制终止重启、横竖屏切换等操作，复现崩溃场景。
• 确保UI操作线程安全：所有UI相关操作必须在主线程执行，排查是否存在后台线程修改视图层级（添加/移除子视图）的情况，避免主线程遍历层级时出错。
• 分析Crashlytics附加信息：查看崩溃设备的iOS版本、机型是否集中在特定范围，以及崩溃前的用户操作路径，缩小问题范围。
• 启用僵尸对象检测：在Xcode中开启Zombie Objects（路径：Edit Scheme -> Diagnostics -> Enable Zombie Objects），复现时若访问已释放对象会直接报错，便于定位问题。
• 检查第三方UI库的视图操作：如果使用了第三方UI库，确认其在场景切换时是否有自动修改视图层级的逻辑，排查可能存在的内存管理问题。

内容的提问来源于stack exchange，提问作者Kakan_Aman