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

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)