避免iOS崩溃：揭秘Unrecognized Selector防护挑战和实用策略

- (void)setContentInset:(UIEdgeInsets)edge {
  [self willChangeValueForKey:@"contentInset"];
  [super setContentInset:edge];
  [self didChangeValueForKey:@"contentInset"];
}

(lldb) breakpoint set -n '[NSObject addObserver:forKeyPath:options:context:]'

Foundation`-[NSObject(NSKeyValueObserverRegistration) addObserver:forKeyPath:options:context:]:
    ......
    0x18aafcd30 <+84>: add x0, x0, #0x3ac ; _NSKeyValueObserverRegistrationLock
    0x18aafcd34 <+88>: mov w1, #0x0
    0x18aafcd38 <+92>: bl 0x1904ce9f0
    0x18aafcd3c <+96>: mov x0, x19
    0x18aafcd40 <+100>: bl 0x1904ce8a0
    0x18aafcd44 <+104>: mov x1, x21
    0x18aafcd48 <+108>: bl 0x18ab3657c ; NSKeyValuePropertyForIsaAndKeyPath
    0x18aafcd4c <+112>: mov x3, x0
    0x18aafcd50 <+116>: mov x0, x19
    0x18aafcd54 <+120>: mov x2, x20
    0x18aafcd58 <+124>: mov x4, x22
    0x18aafcd5c <+128>: mov x5, x23
    0x18aafcd60 <+132>: bl 0x18b3c1c20 ; objc_msgSend$_addObserver:forProperty:options:context:
    0x18aafcd64 <+136>: adrp x0, 376784
    0x18aafcd68 <+140>: add x0, x0, #0x3ac ; _NSKeyValueObserverRegistrationLock
    ......

(lldb) breakpoint set -n 'isaForAutonotifying'

Foundation`-[NSKeyValueUnnestedProperty isaForAutonotifying]:
    ......
    0x18aafd1f8 <+60>: ldrb w8, [x0, x22]
    0x18aafd1fc <+64>: cbz w8, 0x18aafd20c ; <+80>
    0x18aafd200 <+68>: adrp x8, 376776
    0x18aafd204 <+72>: ldrsw x23, [x8, #0x228]
    0x18aafd208 <+76>: b 0x18aafd2bc ; <+256>
    0x18aafd20c <+80>: mov x0, x19
    0x18aafd210 <+84>: bl 0x18b3c49a0 ; objc_msgSend$_isaForAutonotifying
    0x18aafd214 <+88>: adrp x8, 376776
    0x18aafd218 <+92>: add x8, x8, #0x220 ; _MergedGlobals
    0x18aafd21c <+96>: ldrsw x23, [x8, #0x8]
    ......

(lldb) breakpoint set -n '_isaForAutonotifying'

Foundation`-[NSKeyValueUnnestedProperty _isaForAutonotifying]:
    0x18aafd4c0 <+0>: pacibsp 
    0x18aafd4c4 <+4>: stp x20, x19, [sp, #-0x20]!
    0x18aafd4c8 <+8>: stp x29, x30, [sp, #0x10]
    0x18aafd4cc <+12>: add x29, sp, #0x10
    0x18aafd4d0 <+16>: mov x19, x0
    0x18aafd4d4 <+20>: ldp x8, x2, [x0, #0x8]
    0x18aafd4d8 <+24>: ldr x0, [x8, #0x8]
    0x18aafd4dc <+28>: bl 0x18b3c99e0 ; objc_msgSend$automaticallyNotifiesObserversForKey:
    0x18aafd4e0 <+32>: cbz w0, 0x18aafd504 ; <+68>
    0x18aafd4e4 <+36>: ldr x0, [x19, #0x8]
    0x18aafd4e8 <+40>: bl 0x18ab6ad08 ; _NSKeyValueContainerClassGetNotifyingInfo
    0x18aafd4ec <+44>: cbz x0, 0x18aafd508 ; <+72>
    0x18aafd4f0 <+48>: mov x20, x0
    0x18aafd4f4 <+52>: ldr x1, [x19, #0x10]
    0x18aafd4f8 <+56>: bl 0x18aaecbe8 ; _NSKVONotifyingEnableForInfoAndKey
    0x18aafd4fc <+60>: ldr x0, [x20, #0x8]
    0x18aafd500 <+64>: b 0x18aafd508 ; <+72>
    0x18aafd504 <+68>: mov x0, #0x0
    0x18aafd508 <+72>: ldp x29, x30, [sp, #0x10]
    0x18aafd50c <+76>: ldp x20, x19, [sp], #0x20
    0x18aafd510 <+80>: retab

(lldb) breakpoint set -n '_NSKVONotifyingEnableForInfoAndKey'

......
char *argtype = method_copyArgumentType(m, 2);
IMP replacementSetter = (IMP)&_NSSetObjectValueAndNotify;
if (argtype[0] <= '?' && argtype[0] != '#') {
   NSLog(@"KVO only supports -set<Key>: methods that take id, NSNumber-supported scalar types, and some structure types. Autonotifying will not be done for invocations of -[%@ %s].", notifyingInfo->_originalClass, sel_getName(method_getName(m)));
} else {
   if (argtype[0] == '{') {
       if (strcmp(argtype, @encode(CGPoint)) == 0) {
           replacementSetter = (IMP)&_NSSetPointValueAndNotify;
       } else if (strcmp(argtype, @encode(NSRange)) == 0) {
           replacementSetter = (IMP)&_NSSetRangeValueAndNotify;
       } else if (strcmp(argtype, @encode(CGRect)) == 0) {
           replacementSetter = (IMP)&_NSSetRectValueAndNotify;
       } else if (strcmp(argtype, @encode(CGSize)) == 0) {
           replacementSetter = (IMP)&_NSSetSizeValueAndNotify;
       } else {
           replacementSetter = (IMP)&_CF_forwarding_prep_0;
       }
   } else {
       switch (argtype[0]) {
           case: 基础数据类型 {
               // 获取基础数据类型的IMP
               ......
           } break;
       }
   }
   free(argtype);
   SEL selector = method_getName(m);
   NSKVONotifyingSetMethodImplementation(notifyingInfo, selector, replacementSetter, key);
   NSKeyValueSetter *notifyingSetter = [NSObject _createValueSetterWithContainerClassID:notifyingInfo->_notifyingClass key:key];
   [notifyingSetter setMethod:class_getInstanceMethod(notifyingInfo->_notifyingClass, selector)];
   if (replacementSetter == (IMP)&_CF_forwarding_prep_0) {
     NSKVONotifyingSetMethodImplementation(notifyingInfo, @selector(forwardInvocation:), (IMP)&NSKVOForwardInvocation, nil);
       Class otherClass= notifyingInfo->_notifyingClass;
       const char *methodName = sel_getName(selector);
       int nameLength = strlen(methodName);
       const char *prefix = kOriginalImplementationMethodNamePrefix;
       char buffer[29] = {0};
       strlcpy(buffer, prefix, nameLength+strlen(prefix));
       strlcat(buffer, methodName, nameLength+strlen(prefix));
       SEL newForwardingSelector = sel_registerName(buffer);
       IMP originalIMP = method_getImplementation(m);
       const char *originalTypeEncoding = method_getTypeEncoding(m);
       class_addMethod(otherClass, newForwardingSelector, originalIMP, originalTypeEncoding);
   }
}

_CF_forwarding_prep_0: // top of stack is used as marg_list
    stmfd sp!, {r0-r3} // push args to marg_list
    stmfd sp!, {fp, lr} // setup stack frame: sp -= 8, marg_list @ sp+8
    .save {fp, lr}
    .setfp fp, sp, #4
    add fp, sp, #4
    .pad #8
    sub sp, sp, #8          // pad the stack: sp -= 8, marg_list @ sp+16
    add r1, sp, #16         // use marg_list as return strage pointer
    add r0, sp, #16         // load marg_list
    bl ___forwarding___     // call through
    sub sp, fp, #4          // restore stack
    ldmfd sp!, {fp, lr} // destroy stack frame
    cmp r0, #0              // check for forwarding completion
    bne LContinue           // circle back around if we're not done or failed
    ldmfd sp!, {r0-r3} // load return value registers from marg_list
    bx lr                   // return