源码

objc-runtime-new.mm中lookUpImpOrForward方法内：

// No implementation found. Try method resolver once.

    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;
    }

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);
        }
    }
}

动态解析之后，依然后会走消息发送流程(goto retry)
类对象会调用[cls resolveInstanceMethod:sel],元类对象调用[nonMetaClass resolveClassMethod:sel]，然后把这个方法实现，放入class_rw_t的mthods里，注意不是放缓存(除非手动调用)，是放方法二维数组里。

API and Demo

#import <objc/runtime.h>

@implementation MJPerson

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

+ (BOOL)resolveClassMethod:(SEL)sel
{
    if (sel == @selector(test)) {
        // 第一个参数是object_getClass(self)
        class_addMethod(object_getClass(self), sel, (IMP)c_other, "v16@0:8");
        return YES;
    }
    return [super resolveClassMethod:sel];
}

+ (BOOL)resolveInstanceMethod:(SEL)sel
{
    if (sel == @selector(test)) {
        // 动态添加test方法的实现
        class_addMethod(self, sel, (IMP)c_other, "v16@0:8");

        // 返回YES代表有动态添加方法
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

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

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

        // 动态添加test方法的实现
        class_addMethod(self, sel,
                        method_getImplementation(method),
                        method_getTypeEncoding(method));

        // 返回YES代表有动态添加方法
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

 typedef struct objc_method *Method;
 struct objc_method == struct method_t
        struct method_t *otherMethod = (struct method_t *)class_getInstanceMethod(self, @selector(other));

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

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

        // 动态添加test方法的实现
        class_addMethod(self, sel, method->imp, method->types);

        // 返回YES代表有动态添加方法
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}



@end

Runtime(四).动态解析

源码

API and Demo