objc_msgSend()實(shí)現(xiàn)

2.動(dòng)態(tài)解析階段：

1. 判斷之前是否動(dòng)態(tài)解析過(guò)：

• 沒(méi)解析，進(jìn)入判斷，并在解析完成后秘噪，標(biāo)志位置位YES:triedResolver = YES;

 if (resolver  &&  !triedResolver) {
        runtimeLock.unlockRead();
        _class_resolveMethod(cls, sel, inst);
        runtimeLock.read();
        // Don't cache the result; we don't hold the lock so it may have 
        // changed already. Re-do the search from scratch instead.
        triedResolver = YES;
        goto retry;
    }

2. 進(jìn)入動(dòng)態(tài)解析：_class_resolveMethod(cls, sel, inst);

• 根據(jù)你這個(gè)類是類對(duì)象還是元類對(duì)象調(diào)用不同的方法：
• [cls resolveInstanceMethod:sel]
• [nonMetaClass resolveClassMethod:sel]

void _class_resolveMethod(Class cls, SEL sel, id inst) 
{
    if (! cls->isMetaClass()) {
        // try [cls resolveInstanceMethod:sel]
        _class_resolveInstanceMethod(cls, sel, inst);
    } 
    else {
        // try [nonMetaClass resolveClassMethod:sel]
        // and [cls resolveInstanceMethod:sel]
        _class_resolveClassMethod(cls, sel, inst);
        if (!lookUpImpOrNil(cls, sel, inst, 
                            NO/*initialize*/, YES/*cache*/, NO/*resolver*/)) 
        {
            _class_resolveInstanceMethod(cls, sel, inst);
        }
    }
}

如何實(shí)現(xiàn)：

舉例： Person類中只有一個(gè)實(shí)例方法 - (void)test;的聲明；

方法一：

• 直接使用method

- (void)other {
    NSLog(@"%s", __func__);
}

+ (BOOL)resolveInstanceMethod:(SEL)sel {
    if (sel == @selector(test)) {
        // 獲取其他方法
        Method method = class_getInstanceMethod(self, @selector(other));

        // 動(dòng)態(tài)添加test方法的實(shí)現(xiàn)
        class_addMethod(self, sel,
                        method_getImplementation(method),
                        method_getTypeEncoding(method));

        // 返回YES代表有動(dòng)態(tài)添加方法
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

方法二：

• 自定義method_t:

struct method_t {
    SEL sel;
    char *types;
    IMP imp;
};

- (void)other {
    NSLog(@"%s", __func__);
}

+ (BOOL)resolveInstanceMethod:(SEL)sel {
    if (sel == @selector(test)) {
        // 獲取其他方法
        struct method_t *method = (struct method_t *)class_getInstanceMethod(self, @selector(other));

        // 動(dòng)態(tài)添加test方法的實(shí)現(xiàn)
        class_addMethod(self, sel, method->imp, method->types);

        // 返回YES代表有動(dòng)態(tài)添加方法
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

方法三：

• 調(diào)用C語(yǔ)言函數(shù)：

void c_other(id self, SEL _cmd) {
    NSLog(@"c_other - %@ - %@", self, NSStringFromSelector(_cmd));
}

+ (BOOL) resolveInstanceMethod:(SEL)sel {
    if (sel == @selector(test)) {
        // 第一個(gè)參數(shù)是object_getClass(self)
        class_addMethod(self, sel, (IMP)c_other, "v16@0:8");
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

如果是調(diào)用類方法：+ (void)test

+ (BOOL)resolveClassMethod:(SEL)sel {
  
    if (sel == @selector(test)) {
    //object_getClass(self) 獲取當(dāng)前類
    Method methodClass = class_getClassMethod(object_getClass(self), @selector(other));
   
    class_addMethod(object_getClass(self), sel, method_getImplementation(methodClass), method_getTypeEncoding(methodClass));
    return YES;
   }  
 return [super resolveClassMethod:sel];
}

動(dòng)態(tài)解析流程圖：

1. 先判斷該方法是否進(jìn)行過(guò)動(dòng)態(tài)解析；
2. 如果沒(méi)有烫堤，調(diào)用+ (BOOL) resolveInstanceMethod:(SEL)sel或+ (BOOL)resolveClassMethod:(SEL)sel來(lái)進(jìn)行動(dòng)態(tài)方法解析；
3. 動(dòng)態(tài)方法解析如果有實(shí)現(xiàn)：會(huì)有一個(gè)class_addMethod函數(shù)，將方法添加到類對(duì)象的class_rw_t的methods;
4. 不管動(dòng)態(tài)方法解析階段有沒(méi)有方法實(shí)現(xiàn)鸽斟，是否進(jìn)行過(guò)動(dòng)態(tài)解析標(biāo)志位都會(huì)置為YES:triedResolver = YES;
5. 并再返回第一步消息發(fā)送階段,進(jìn)行方法查找：goto retry:
   1. 如果動(dòng)態(tài)解析有方法實(shí)現(xiàn)拔创，方法查找階段就會(huì)在class_rw_t的methods中找到方法；
   2. 如果動(dòng)態(tài)解析方法沒(méi)有實(shí)現(xiàn)富蓄，方法仍舊找不到剩燥；
6. 進(jìn)入消息轉(zhuǎn)發(fā)階段。