我在以下回溯中遇到了很多崩溃，但我找不到原因。
根据 Apple -[NSObject(NSObject) doesNotRecognizeSelector:]，当新对象被分配到先前由已释放对象占用的内存中时，就会发生这种情况。
Note: Messaging a previously deallocated object may raise an NSInvalidArgumentException instead of crashing the program with a memory access violation. This occurs when a new object is allocated in the memory previously occupied by the deallocated object. If your application is crashing due to an uncaught NSInvalidArgumentException (look for -[NSObject(NSObject) doesNotRecognizeSelector:] in the exception backtrace), consider profiling your application with the Zombies instrument to eliminate the possibility that improper memory management is the cause.
https://developer.apple.com/library/archive/technotes/tn2151/_index.html
但是回溯的其余部分是怎么回事，尤其是 -[UIUndoGestureInteraction didMoveToView:] 事情？
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Triggered by Thread: 0
Last Exception Backtrace:
0 CoreFoundation 0x1ae45498c __exceptionPreprocess + 220 (NSException.m:199)
1 libobjc.A.dylib 0x1ae17d0a4 objc_exception_throw + 56 (objc-exception.mm:565)
2 CoreFoundation 0x1ae35843c -[NSObject(NSObject) doesNotRecognizeSelector:] + 140 (NSObject.m:144)
3 UIKitCore 0x1b24902a8 -[UIResponder doesNotRecognizeSelector:] + 296 (UIResponder.m:659)
4 CoreFoundation 0x1ae458e08 ___forwarding___ + 1324 (NSForwarding.m:3325)
5 CoreFoundation 0x1ae45abec _CF_forwarding_prep_0 + 92
6 UIKitCore 0x1b2353040 -[UIUndoGestureInteraction didMoveToView:] + 108 (UIUndoGestureInteraction.m:725)
7 UIKitCore 0x1b28eb3c4 _setInteractionView + 84 (UIView.m:16421)
8 UIKitCore 0x1b28eb2a0 -[UIView(Dragging) addInteraction:] + 268 (UIView.m:16450)
9 UIKitCore 0x1b26cd2b8 -[UIEditingOverlayViewController _addInteractions] + 260 (UIEditingOverlayViewController.m:79)
10 UIKitCore 0x1b1e5b2ec -[UIViewController _setViewAppearState:isAnimating:] + 832 (UIViewController.m:4695)
11 UIKitCore 0x1b1e5b6fc __52-[UIViewController _setViewAppearState:isAnimating:]_block_invoke + 268 (UIViewController.m:4758)
12 CoreFoundation 0x1ae42773c __NSARRAY_IS_CALLING_OUT_TO_A_BLOCK__ + 16 (NSArrayHelpers.m:9)
13 CoreFoundation 0x1ae32b86c -[__NSArrayI enumerateObjectsWithOptions:usingBlock:] + 152 (NSArrayI.m:108)
14 UIKitCore 0x1b1e5b49c -[UIViewController _setViewAppearState:isAnimating:] + 1264 (UIViewController.m:4736)
15 UIKitCore 0x1b1e5d530 __64-[UIViewController viewDidMoveToWindow:shouldAppearOrDisappear:]_block_invoke + 44 (UIViewController.m:5272)
16 UIKitCore 0x1b1e5c32c -[UIViewController _executeAfterAppearanceBlock] + 88 (UIViewController.m:5050)
17 UIKitCore 0x1b246bca4 _runAfterCACommitDeferredBlocks + 584 (UIApplication.m:3027)
18 UIKitCore 0x1b245b7c0 _cleanUpAfterCAFlushAndRunDeferredBlocks + 232 (UIApplication.m:2986)
19 UIKitCore 0x1b248b594 _afterCACommitHandler + 76 (UIApplication.m:3048)
20 CoreFoundation 0x1ae3d1c48 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32 (CFRunLoop.c:1758)
21 CoreFoundation 0x1ae3ccb34 __CFRunLoopDoObservers + 416 (CFRunLoop.c:1868)
22 CoreFoundation 0x1ae3cd100 __CFRunLoopRun + 1308 (CFRunLoop.c:2910)
23 CoreFoundation 0x1ae3cc8bc CFRunLoopRunSpecific + 464 (CFRunLoop.c:3192)
24 GraphicsServices 0x1b8238328 GSEventRunModal + 104 (GSEvent.c:2246)
25 UIKitCore 0x1b24626d4 UIApplicationMain + 1936 (UIApplication.m:4753)
26 JustConnect 0x10425ca60 main + 68 (APIInfoUser.swift:7)
27 libdyld.dylib 0x1ae257460 start + 4
最佳答案
以下是 Apple 开发人员和技术支持人员的回复:
The key thing to notice here is that frames 0 through 5 of this backtrace are just boilerplate associated with an unrecognised selector. That is, frame 6 has called a method on an object, the object didn’t recognise that selector so it entered the Objective-C runtime forwarding infrastructure (frames 5 through 4). That landed in UIResponder (frame 3) because UIResponder support some sort of generic message forwarding. That message forwarding failed, so UIResponder called super (frame 2), which then threw the exception.
So the real question is, what’s going on in frame 6. To learn more about this, you can disassemble the code (-:
(lldb) disas -n '-[UIUndoGestureInteraction didMoveToView:]' UIKitCore`-[UIUndoGestureInteraction didMoveToView:]: 0x1bbe92fd4 <+0>: stp x22, x21, [sp, #-0x30]! 0x1bbe92fd8 <+4>: stp x20, x19, [sp, #0x10] 0x1bbe92fdc <+8>: stp x29, x30, [sp, #0x20] 0x1bbe92fe0 <+12>: add x29, sp, #0x20 ; =0x20 0x1bbe92fe4 <+16>: mov x21, x2 0x1bbe92fe8 <+20>: mov x19, x0 0x1bbe92fec <+24>: add x20, x0, #0x10 ; =0x10 0x1bbe92ff0 <+28>: mov x0, x20 0x1bbe92ff4 <+32>: mov x1, x2 0x1bbe92ff8 <+36>: bl 0x1b7cd71d8 ; objc_storeWeak 0x1bbe92ffc <+40>: cbz x21, 0x1bbe930a8 ; <+212> 0x1bbe93000 <+44>: adrp x8, 208464 0x1bbe93004 <+48>: add x1, x8, #0x7b1 ; =0x7b1 0x1bbe93008 <+52>: mov x0, x19 0x1bbe9300c <+56>: bl 0x1b7cb9180 ; objc_msgSend 0x1bbe93010 <+60>: mov x0, x20 0x1bbe93014 <+64>: bl 0x1b7cd7a80 ; objc_loadWeakRetained 0x1bbe93018 <+68>: mov x20, x0 0x1bbe9301c <+72>: adrp x8, 208304 0x1bbe93020 <+76>: add x1, x8, #0xc04 ; =0xc04 0x1bbe93024 <+80>: bl 0x1b7cb9180 ; objc_msgSend 0x1bbe93028 <+84>: mov x29, x29 0x1bbe9302c <+88>: bl 0x1b7cd8864 ; objc_retainAutoreleasedReturnValue 0x1bbe93030 <+92>: mov x21, x0 0x1bbe93034 <+96>: adrp x8, 208502 0x1bbe93038 <+100>: add x1, x8, #0xbb7 ; =0xbb7 0x1bbe9303c <+104>: bl 0x1b7cb9180 ; objc_msgSend 0x1bbe93040 <+108>: stp d0, d1, [x19, #0x100]There’s a bunch of things you can learn here. First, frame 6 in the backtrace has an offset of +108, so that actual call that failed is at +104. An objc_msgSend, has two standard parameters, the target object and the selector. On 64-bit Arm these map to x0 and x1, respectively.
Let’s look at the selector first. This is constructed by the two instructions at +96 and +100. Those two instructions form a PC-relative address. The adrp instruction (‘add relative to page’) takes the current PC (0x1bbe93034), clears the bottom 12 bits (0x1bbe93000, remember that the historical page size is 4096 [1]), and then takes the literal, shifts it left by 12 bits (208502 << 12), and then adds it in. The add instruction is much simpler. It takes the result from the previous calculation and adds 0xbb7 (note the switch from decimal to hex!).
If you run this calculation in the debugger you’ll see this:
(lldb) p (char*)( 0x1bbe93000+(208502<<12)+0xbb7) (char *) $1 = 0x00000001eed09bb7 "actualSceneBounds"So the selector is actualSceneBounds. Cool.
Now let’s look at the object. At the time of the call (+104) this is expected to be in x0. At +92 we see it copy x0 to x21, but this is just a distraction. Actually x0 is the function result from objc_retainAutoreleasedReturnValue at +88. That function takes and returns an object, so x0 is the value returned by the message send at +80. Doing the same relative page trick we did earlier, we see that the selector for that call is -window. But what object is that being called on?
Working that out is… well… kinda complex because of the objc_storeWeak / objc_loadWeakRetained dance. I believe it boils down to the value passed into this method via x2, that is, the third parameter. Based on the method name, this is clearly a view (remember that, for Objective-C methods, the first two parameters, x0 and x1, hold the target and the selector, so x2 holds the first actual parameter).
So, in summary:
It seems that this method has a view parameter.
It’s requested window.window.screenBounds.
The last property access has failed because the thing that’s meant to be a window doesn’t implement the -screenBounds getter.
I don’t know enough about UIKit to explain the background to that. I have a couple of suggestions here:
Run the Standard Memory Debugging Tools, and specifically Zombies, to see if they turn up anything useful. Make sure to exercise the undo gesture, based on the class name of the method we pulled apart.
If that doesn’t pan out, bounce over to App Frameworks > Cocoa Touch to see if anyone there has any suggestions.
Share and Enjoy
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[1] On 64-bit Arm the actual page size is typically 64 KiB, but the adrp instruction uses the historical page size of 4096 because it matches the maximum literal size in the add instruction.
关于ios - UIResponder 不识别选择器，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/58408690/