预防 app crash 之 unrecognized selector

处理unrecognized selector异常原因

假如封装一个方法，在其他模块调用该方法时，传入参数不匹配则crash。比如下面的方法：本应该传入的参数类型为NSMutableArray，如果传入的参数类型是NSArray，导致抛出 unrecognized selector异常

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- (void)doSomethingWithArray:(NSMutableArray *)arr{
[arr addObject:@"123"];
}

当然，通过 参数类型判断 也可以避免问题的发生：

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- (void)doSomethingWithArray:(NSMutableArray *)arr{
if ([arr isKindOfClass:[NSMutableArray class]]) {
[arr addObject:@"123"];
}else{
CrashOnSimulator(@"⚠️参数类型不对哦⚠️");
}
}

crash提醒：

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void CrashOnSimulator(NSString *errorMsg) {
if((TARGET_OS_SIMULATOR)){raise(SIGSTOP);}
}

但是，有点地方可能忘记类型判断了怎么办，有全局拦截unrecognized selector 异常的方案吗？

分析 如何全局拦截unrecognized selector 异常

logo

oc的消息发送机制咱们都熟悉了，通过superclass指针逐级向上查找该消息所对应的方法实现，如果遇到找不的方法，还有三次补救机制。我们可以通过上面三种方法中的一种，就可以避免unrecognized selector sent to instance

第一种方法：重写 NSObject 的forwardingTargetForSelector:

⚠️filter unrecoginze seletor of intance only

思路

  • 创建一个接收未知消息的类，暂且称之为Protector
  • 创建一个NSObject 的分类，在分类中重写forwardingTargetForSelector: ，在这个方法中截获未实现的方法，转发给Protector。并为Protector 动态的添加未实现的方法，最后返回Protector 的实例对象。
  • 在分类中新增一个安全的方法实现，来作为Protector 接收到的未知消息的实现

代码

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#import "NSObject+Protector.h"
#import <objc/runtime.h>
@implementation NSObject (Protector)
 
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-protocol-method-implementation"
- (id)forwardingTargetForSelector:(SEL)aSelector{
 
if ([self isCurrentClassInWhiteList]) {
[[self class] warningDeveloper:aSelector];
 
Class protectorCls = NSClassFromString(@"ProtectorClassName");
if (!protectorCls){
protectorCls = objc_allocateClassPair([NSObject class], "ProtectorClassName", 0);
objc_registerClassPair(protectorCls);
}
 
if (![self isExistSelector:aSelector inClass:protectorCls]){
class_addMethod(protectorCls, aSelector, [self safeImplementation:aSelector],[NSStringFromSelector(aSelector) UTF8String]);
}
 
Class Protector = [protectorCls class];
id instance = [[Protector alloc] init];
return instance;
} else {
return nil;
}
}
#pragma clang diagnostic pop
 
- (BOOL)isCurrentClassInWhiteList{
NSArray *classNameArray = @[@"NSNull",@"NSString",@"NSArray",@"NSDictionary",@"NSURL"];
for (NSString *className in classNameArray) {
if ([self isKindOfClass:NSClassFromString(className)]) {
return YES;
}
}
return NO;
}
 
- (BOOL)isExistSelector: (SEL)aSelector inClass:(Class)currentClass{
BOOL isExist = NO;
unsigned int methodCount = 0;
Method *methods = class_copyMethodList(currentClass, &methodCount);
for (int i = 0; i < methodCount; i++){
Method temp = methods[i];
SEL sel = method_getName(temp);
NSString *methodName = NSStringFromSelector(sel);
if ([methodName isEqualToString: NSStringFromSelector(aSelector)]){
isExist = YES;
break;
}
}
return isExist;
}
 
- (IMP)safeImplementation:(SEL)aSelector{
IMP imp = imp_implementationWithBlock(^(){
NSLog(@"PROTECTOR: %@ Done", NSStringFromSelector(aSelector));
});
return imp;
}
 
+ (void)warningDeveloper:(SEL)aSelector{
#if DEBUG
NSString *selectorStr = NSStringFromSelector(aSelector);
NSLog(@"PROTECTOR: -[%@ %@]", [self class], selectorStr);
NSLog(@"PROTECTOR: unrecognized selector \"%@\" sent to instance: %p", selectorStr, self);
NSLog(@"PROTECTOR: call stack: %@", [NSThread callStackSymbols]);
// @throw @"方法找不到";
#endif
}
 
@end

第二种方法：重写 NSObject 的methodSignatureForSelector(有些问题，下面有个最终版)

😄filter unrecoginze seletor of class and intance
but 如果你使用了JSPatch、Aspects等对methodSignatureForSelector进行swizzle的第三方库，就别用这种方案了，有冲突，出现莫名的错误

思路

  • 创建NSObject+Protector重写methodSignatureForSelector，判断current class是否在白名单？
    • YES:返回一个空签名，啥也不做
    • NO:返回正常的签名，走原来的逻辑

代码

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#import "NSObject+Protector.h"
#import <objc/runtime.h>
@implementation NSObject (Protector)
 
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-protocol-method-implementation"
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
return [[self class] __getMethodSignatureForSelector:aSelector];
}
 
- (void)forwardInvocation:(NSInvocation *)anInvocation{
}
#pragma clang diagnostic pop
 
+ (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
return [self __getMethodSignatureForSelector:aSelector];
}
 
+ (void)forwardInvocation:(NSInvocation *)anInvocation{
}
 
+ (NSMethodSignature *)__getMethodSignatureForSelector:(SEL)aSelector{
if ([self isSubclassInWhiteListClass]) {
[self warningDeveloper:aSelector];
return [NSMethodSignature signatureWithObjCTypes:"@"];
}else{
return [self instanceMethodSignatureForSelector:aSelector];
}
}
 
+ (BOOL)isSubclassInWhiteListClass{
NSArray *classNameArray = @[@"NSNull",@"NSString",@"NSArray",@"NSDictionary",@"NSURL"];
for (NSString *className in classNameArray) {
if ([self isSubclassOfClass:NSClassFromString(className)]) {
return YES;
}
}
return NO;
}
 
+ (void)warningDeveloper:(SEL)aSelector{
#if DEBUG
NSString *selectorStr = NSStringFromSelector(aSelector);
NSLog(@"PROTECTOR: -[%@ %@]", [self class], selectorStr);
NSLog(@"PROTECTOR: unrecognized selector \"%@\" sent to instance: %p", selectorStr, self);
NSLog(@"PROTECTOR: call stack: %@", [NSThread callStackSymbols]);
// @throw @"方法找不到";
#endif
}

第三种方法：最终方案(解决methodSignatureForSelector的不足)

第三方库对 methodSignatureForSelector进行了全局替换，而我们也在NSObject中 进行了全局替换，冲突的点在于我们影响了第三库的自定义的Class。<br\>

  • 如何避免呢？ 我们替换常用的的几个class就行了呗，是的，不过工作量有点大且重复，怎么办？用 define 来解决，如下：
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// NSArray+WBGProtector.m
 
#import "NSArray+WBGProtector.h"
#import <objc/runtime.h>
 
#define WBG_PROTECT_CLASS_NAME(_classname_)\
@implementation _classname_ (WBGProtector)\
\
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{\
return [[self class] __getMethodSignatureForSelector:aSelector type:@"instance"];\
}\
\
- (void)forwardInvocation:(NSInvocation *)anInvocation{\
}\
\
+ (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{\
return [self __getMethodSignatureForSelector:aSelector type:@"class"];\
}\
\
+ (void)forwardInvocation:(NSInvocation *)anInvocation{\
}\
\
+ (NSMethodSignature *)__getMethodSignatureForSelector:(SEL)aSelector type:(id)type{\
NSString *errorMsg = [NSString stringWithFormat:@"PROTECTOR: -[%@ %@],unrecognized selector sent to %@",self,NSStringFromSelector(aSelector),type];\
NSLog(@"%@",errorMsg);\
CrashOnSimulator(errorMsg);\
return [NSMethodSignature signatureWithObjCTypes:"@"];\
}\
\
@end\
 
 
WBG_PROTECT_CLASS_NAME(NSArray)
WBG_PROTECT_CLASS_NAME(NSDictionary)
WBG_PROTECT_CLASS_NAME(NSString)

细节分析

为什么需要白名单？

在app启动加载一些系统方法，总是莫名其名的 报错 甚至crash
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为什么去掉UIResponder?

isCurrentClassInWhiteList 中的classNameArray 本来是有 UIResponder的，但是后来测试发现UIWebView会出现异常！这里把UIResponder去掉了，毕竟过滤大部分的unrecognize selector主要的是NSArray和NSDictionary
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测试code

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// test Class method
id clazz = [NSArray class];
[clazz viewDidLoad];
 
// test instance method
NSMutableArray *arr = @{};
[arr addObject:@""]

遗留问题

    • 需要判断自己项目中引入的第三方库没有通过category的方式去重写NSObject的方法methodSignatureForSelector /forwardInvocation 以及forwardingTargetForSelector
      • 原因：一个category也不能可靠的覆盖另一个category中相同的类的相同的方法。例如UIViewController+A与UIViewController+B，都重写了viewDidLoad，我们就无法控制谁覆盖了谁。
    • 如果第三方重写了，则在这里通过swizzling的方式 替换 具体的实现方法
posted @ 2017-06-23 12:01  FMDN  阅读(1405)  评论(0)    收藏  举报