*main.m

PersonA *personA = [[PersonA alloc]init];
[personA speechJapan];

• PersonB.h

- (void)speechJapan;

• PersonB.m

- (void)speechJapan{
    NSLog(@"speechJapan");
}

• PersonA.h

- (void)speechEnglish;
- (void)speechJapan;

• PersonA.m

- (void)speechEnglish{
    NSLog(@"speechEnglist");
}

// 此方法不是方法的實(shí)現(xiàn)捞魁，需要進(jìn)行轉(zhuǎn)化
- (void)speechNewLan{
     NSLog(@"speechNewLan");
}

// 將方法轉(zhuǎn)換成方法的實(shí)現(xiàn)IMP
IMP convertToIMP(){
    return  class_getMethodImplementation([PersonA class], @selector(speechNewLan));
}
/* 當(dāng)未找到speechJapan時(shí)钾菊，首先調(diào)用此方法，使有機(jī)會(huì)添加一個(gè)實(shí)現(xiàn)的方法
 如果添加了方法并且放回了Yes磺箕，則運(yùn)行時(shí)系統(tǒng)會(huì)啟用一次消息發(fā)送的過(guò)程稽屏。如果返回為NO,
 運(yùn)行時(shí)系統(tǒng)則進(jìn)入到下一步扮宠，消息轉(zhuǎn)發(fā)（Message Forwarding）
 */

// 消息派發(fā)
+ (BOOL)resolveInstanceMethod:(SEL)sel{
    if (sel == @selector(speechJapan)) {
        class_addMethod(self, sel, convertToIMP(), "");
        return YES;
    }
    return NO;
}


/*實(shí)現(xiàn)此方法，運(yùn)行時(shí)系統(tǒng)就會(huì)調(diào)用次方法诫欠，將消息轉(zhuǎn)發(fā)給其他指定的對(duì)象涵卵，
 比如轉(zhuǎn)發(fā)給PersonB的對(duì)象
 
注：只要返回的對(duì)象不是nil或self浴栽，消息發(fā)送的整個(gè)過(guò)程就會(huì)啟動(dòng)
 發(fā)送的對(duì)象變?yōu)橹付ǚ祷氐膶?duì)象，比如PersonB轿偎。如果返回的是nil或self典鸡，則進(jìn)行下一步轉(zhuǎn)發(fā)操作
 */
- (id)forwardingTargetForSelector:(SEL)aSelector{
    if (aSelector == @selector(speechJapan)) {
        PersonB *pB = [[PersonB alloc] init];
        return pB;
    }
    return [super forwardingTargetForSelector:aSelector];
}

// 消息轉(zhuǎn)發(fā)第二步 Mormal forwrading

/* 獲取方法簽名
 調(diào)用此方法獲取函數(shù)的參數(shù)和返會(huì)類型,如果此方法返回nil
 Runtime則會(huì)發(fā)出doseNotRecognizeSelector: 消息掛掉程序
 如果返回一個(gè)函數(shù)簽名，Runtime則會(huì)創(chuàng)建一個(gè)NSINvocation對(duì)象坏晦，調(diào)用ForwradInvacation:
 發(fā)送消息給對(duì)象
 */
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
    
    NSMethodSignature *sign = [[PersonB class] instanceMethodSignatureForSelector:aSelector];
    return [NSMethodSignature signatureWithObjCTypes:"v@:"];
}

// 實(shí)現(xiàn)消息的轉(zhuǎn)發(fā)
/*
 NSInvocation 實(shí)際上是對(duì)一個(gè)消息的描述萝玷，包括selector極其參數(shù)等信息
 所以可以在此方法中修改NSInvocation對(duì)象，然后調(diào)用invokeWithTarget:消息給對(duì)象
 */
- (void)forwardInvocation:(NSInvocation *)anInvocation{
    SEL sel = anInvocation.selector;
     PersonB *pB = [[PersonB alloc] init];
    if ([pB respondsToSelector:sel]) {
        [anInvocation invokeWithTarget:pB];
    }else{
        [self doesNotRecognizeSelector:sel];
    }
}