消息转发

先提出疑问这个方法是怎么来的？

• lookUpImpOrForward jump

• log_and_fill_cache jump 填充缓存

• logMessageSend jump

• instrumentObjcMessageSends jump

所以extern void instrumentObjcMessageSends(BOOL flag);就是将里面的方法，做了外部扩展，传值YES/NO

接下来在HLPerson.m文件中添加forwardingTargetForSelector方法 — 快速转发

//输出
-[HLPerson forwardingTargetForSelector:] *** sayNB
 -[HLPerson sayNB]: unrecognized selector sent to instance 0x100a72f70
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修改返回值， HLTeacher 类有- (void)teacherSay方法 — 快速转发

//快速转发
- (id) TargetForSelector:(SEL)aSelector{
    
    NSLog(@"%s *** %@",__func__,NSStringFromSelector(aSelector));
    
    return [HLTeacher alloc];
    
}
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//输出
-[HLPerson forwardingTargetForSelector:] *** sayNB
-[HLTeacher teacherSay]
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//慢速转发
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
   
    NSLog(@"%s --- %@",__func__,NSStringFromSelector(aSelector));
   
    if (aSelector == @selector(sayNB)) {
        
        return [NSMethodSignature signatureWithObjCTypes:"v@:"];
 
    }
    
    return [super methodSignatureForSelector:aSelector];
    
}
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//输出
 -[HLPerson methodSignatureForSelector:] --- sayNB

- (void)forwardInvocation:(NSInvocation *)anInvocation{
    
    NSLog(@"%@ ### %@",anInvocation.target,NSStringFromSelector(anInvocation.selector));
    
}
-[HLPerson methodSignatureForSelector:] --- sayNB
 <HLPerson: 0x101547e20> ### sayNB
Program ended with exit code: 0
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//添加respondsToSelector判断
- (void)forwardInvocation:(NSInvocation *)anInvocation{
    
//    NSLog(@"%@ ### %@",anInvocation.target,NSStringFromSelector(anInvocation.selector));
    
    HLTeacher *t = [HLTeacher alloc];
    
    if ([self respondsToSelector:anInvocation.selector]) {
        [anInvocation invoke];
    }else if ([t respondsToSelector:anInvocation.selector]){
        [anInvocation invokeWithTarget:t];
    }else{
        NSLog(@"%s --- %@",__func__,NSStringFromSelector(anInvocation.selector));
        [anInvocation invoke];
    }
    
}
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现在把上面的快速和慢速方法先注释，看下lldb

//报错的关键
  frame #10: 0x00007fff2059b90b CoreFoundation`___forwarding___ + 1448
  frame #11: 0x00007fff2059b2d8 CoreFoundation`_CF_forwarding_prep_0 + 120
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未完待续…