消息转发流程分析

static NEVER_INLINE IMP  
resolveMethod_locked(id inst, SEL sel, Class cls, int behavior)  
{  
    runtimeLock.assertLocked();  
    ASSERT(cls->isRealized());  
    runtimeLock.unlock();  
    // 动态方法决议 : 给一次机会 重新查询  
    if (! cls->isMetaClass()) {  // 对象 - 类  
        // try [cls resolveInstanceMethod:sel]  
        resolveInstanceMethod(inst, sel, cls);  
    } 
    else { // 类方法 - 元类  
        // try [nonMetaClass resolveClassMethod:sel]  
        // and [cls resolveInstanceMethod:sel]  
        resolveClassMethod(inst, sel, cls);  
        if (!lookUpImpOrNil(inst, sel, cls)) {  // 为什么要有这行代码  ,因为类其实是元类的对象. 所以又执行了对象方法的查找流程
            resolveInstanceMethod(inst, sel, cls);  
        }  
    }  
    // chances are that calling the resolver have populated the cache   
    // so attempt using it  
    return lookUpImpOrForward(inst, sel, cls, behavior | LOOKUP_CACHE);  
}

#import <Foundation/Foundation.h>  
#import "LGPerson.h"  
// 慢速查找   
extern void instrumentObjcMessageSends(BOOL flag);  
int main(int argc, const char * argv[]) {  
    @autoreleasepool {  
        LGPerson *person = [LGPerson alloc];  
        instrumentObjcMessageSends(YES);  
        [person sayHello];  
        instrumentObjcMessageSends(NO);  
        NSLog(@"Hello, World!");  
    }  
    return 0;  
}

+ LGPerson NSObject resolveInstanceMethod:  
+ LGPerson NSObject resolveInstanceMethod:  
- LGPerson NSObject forwardingTargetForSelector:  
- LGPerson NSObject forwardingTargetForSelector:  
- LGPerson NSObject methodSignatureForSelector:  
- LGPerson NSObject methodSignatureForSelector:  
- LGPerson NSObject class  
+ LGPerson NSObject resolveInstanceMethod:  
+ LGPerson NSObject resolveInstanceMethod:  
- LGPerson NSObject doesNotRecognizeSelector:  
- LGPerson NSObject doesNotRecognizeSelector:  
- LGPerson NSObject class  
- OS_xpc_serializer OS_xpc_object dealloc  
- OS_object NSObject dealloc  
+ OS_xpc_payload NSObject class  
- OS_xpc_payload OS_xpc_payload dealloc  
- NSObject NSObject dealloc  
- OS_dispatch_mach_msg OS_dispatch_object dealloc  
- OS_xpc_dictionary OS_xpc_object dealloc  
+ OS_xpc_mach_send NSObject initialize  
- OS_xpc_mach_send OS_xpc_object dealloc  
- OS_object NSObject dealloc  
- OS_object NSObject dealloc

+ (BOOL)resolveInstanceMethod:(SEL)sel{  
    NSLog(@"%@ 来了",NSStringFromSelector(sel));  
    if (sel == @selector(say666)) {  
        NSLog(@"%@ 来了",NSStringFromSelector(sel));  
        IMP imp           = class_getMethodImplementation(self, @selector(sayMaster));  
        Method sayMMethod = class_getInstanceMethod(self, @selector(sayMaster));  
        const char *type  = method_getTypeEncoding(sayMMethod);  
        return class_addMethod(self, sel, imp, type);  
    }
    return [super resolveInstanceMethod:sel];  
}

+ (BOOL)resolveClassMethod:(SEL)sel{  
    NSLog(@"%@ 来了",NSStringFromSelector(sel));  
    if (sel == @selector(sayNB)) {  
        IMP imp           = class_getMethodImplementation(objc_getMetaClass("LGPerson"), @selector(lgClassMethod));  
        Method sayMMethod = class_getInstanceMethod(objc_getMetaClass("LGPerson"), @selector(lgClassMethod));  
        const char *type  = method_getTypeEncoding(sayMMethod);  
        return class_addMethod(objc_getMetaClass("LGPerson"), sel, imp, type);  
    }  
    return [super resolveClassMethod:sel];  
}

#import "NSObject+LG.h"  
#import <objc/message.h>  
@implementation NSObject (LG)  
// 调用方法的时候 - 分类  
+ (BOOL)resolveInstanceMethod:(SEL)sel{  
    NSLog(@"%@ 来了",NSStringFromSelector(sel));  
    if (sel == @selector(say666)) {  
        NSLog(@"%@ 来了",NSStringFromSelector(sel));  
        IMP imp           = class_getMethodImplementation(self, @selector(sayMaster));  
        Method sayMMethod = class_getInstanceMethod(self, @selector(sayMaster));  
        const char *type  = method_getTypeEncoding(sayMMethod);  
        return class_addMethod(self, sel, imp, type);  
    }  
    else if (sel == @selector(sayNB)) {  
        IMP imp           = class_getMethodImplementation(objc_getMetaClass("LGPerson"), @selector(lgClassMethod));  
        Method sayMMethod = class_getInstanceMethod(objc_getMetaClass("LGPerson"), @selector(lgClassMethod));  
        const char *type  = method_getTypeEncoding(sayMMethod);  
        return class_addMethod(objc_getMetaClass("LGPerson"), sel, imp, type);  
    }  
    return NO;  
}
/**
 1: 分类 - 便利
 2: 方法 - lg_model_tracffic
        - lg - model home - 奔溃 - pop Home
        - lg - mine  - mine
    切面 - SDK - 上传
 3: AOP - 封装SDK - 不处理
 4: 消息转发 - 
 */

- (id)forwardingTargetForSelector:(SEL)aSelector{  
    NSLog(@"%s - %@",__func__,NSStringFromSelector(aSelector));  
    if(aSelector == @selector(sayBad)){  
        return [LGStudent sayHello];  
    }  
    // runtime + aSelector + addMethod + imp  
    return [super forwardingTargetForSelector:aSelector];  
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{  
    NSLog(@"%s - %@",__func__,NSStringFromSelector(aSelector));  
    return nil;  
}  
- (void)forwardInvocation:(NSInvocation *)anInvocation{  
    NSLog(@"%s - %@",__func__,anInvocation);  
    // GM  sayHello - anInvocation - 漂流瓶 - anInvocation  
    anInvocation.target = [LGStudent alloc];  
    // anInvocation 保存 - 方法  
    [anInvocation invoke];  
}