面试题: 方法的存储

@interface LGPerson : NSObject
- (void)sayHello;
+ (void)sayHappy;
@end

@implementation LGPerson
- (void)sayHello{
    NSLog(@"LGPerson say : Hello!!!");
}

+ (void)sayHappy{
    NSLog(@"LGPerson say : Happy!!!");
}
@end

       LGPerson *person = [LGPerson alloc];
        Class pClass     = object_getClass(person);
        lgObjc_copyMethodList(pClass);

        lgInstanceMethod_classToMetaclass(pClass);
        lgClassMethod_classToMetaclass(pClass);
        NSLog(@"Hello, World!");

lgObjc_copyMethodList 函数：用于获取类的方法列表

void lgObjc_copyMethodList(Class pClass){
    unsigned int count = 0;
    Method *methods = class_copyMethodList(pClass, &count);
    for (unsigned int i=0; i < count; i++) {
        Method const method = methods[i];
        //获取方法名
        NSString *key = NSStringFromSelector(method_getName(method));
        
        LGLog(@"Method, name: %@", key);
    }
    free(methods);
}

lgInstanceMethod_classToMetaclass 函数：用于获取类的实例方法

void lgInstanceMethod_classToMetaclass(Class pClass){
    
    const char *className = class_getName(pClass);
    Class metaClass = objc_getMetaClass(className);
    
    Method method1 = class_getInstanceMethod(pClass, @selector(sayHello));
    Method method2 = class_getInstanceMethod(metaClass, @selector(sayHello));

    Method method3 = class_getInstanceMethod(pClass, @selector(sayHappy));
    Method method4 = class_getInstanceMethod(metaClass, @selector(sayHappy));
    
    LGLog(@"%s - %p-%p-%p-%p",__func__,method1,method2,method3,method4);
}

lgClassMethod_classToMetaclass 函数：用于获取类的类方法

void lgClassMethod_classToMetaclass(Class pClass){
    
    const char *className = class_getName(pClass);
    Class metaClass = objc_getMetaClass(className);
    
    Method method1 = class_getClassMethod(pClass, @selector(sayHello));
    Method method2 = class_getClassMethod(metaClass, @selector(sayHello));

    Method method3 = class_getClassMethod(pClass, @selector(sayHappy));//1
    // 元类 为什么有 sayHappy 类方法 0 1
    //
    Method method4 = class_getClassMethod(metaClass, @selector(sayHappy));//1
    
    LGLog(@"%s-%p-%p-%p-%p",__func__,method1,method2,method3,method4);
}

lgIMP_classToMetaclass 函数：用于获取方法的实现

void lgIMP_classToMetaclass(Class pClass){
    
    const char *className = class_getName(pClass);
    Class metaClass = objc_getMetaClass(className);

    // - (void)sayHello;
    // + (void)sayHappy;
    IMP imp1 = class_getMethodImplementation(pClass, @selector(sayHello));
    IMP imp2 = class_getMethodImplementation(metaClass, @selector(sayHello));

    IMP imp3 = class_getMethodImplementation(pClass, @selector(sayHappy));
    IMP imp4 = class_getMethodImplementation(metaClass, @selector(sayHappy));

    NSLog(@"%p-%p-%p-%p",imp1,imp2,imp3,imp4);
    NSLog(@"%s",__func__);
}

最后打印结果:

图片.png

分析

先看下两个方法

class_getClassMethod 获取类方法 == 元类中查找实例方法

Method class_getClassMethod(Class cls, SEL sel)
{
    if (!cls  ||  !sel) return nil;
    //从类的元类中查找实例方法
    return class_getInstanceMethod(cls->getMeta(), sel);
}

    Class getMeta() {//如果类是元类, 这返回自己
        if (isMetaClass()) return (Class)this;
        else return this->ISA();
    }

class_getInstanceMethod

Method class_getInstanceMethod(Class cls, SEL sel)
{
    if (!cls  ||  !sel) return nil;

    // This deliberately avoids +initialize because it historically did so.

    // This implementation is a bit weird because it's the only place that 
    // wants a Method instead of an IMP.

#warning fixme build and search caches
        
    // Search method lists, try method resolver, etc.
    lookUpImpOrForward(nil, sel, cls, LOOKUP_RESOLVER);

#warning fixme build and search caches

    return _class_getMethod(cls, sel);
}


static Method _class_getMethod(Class cls, SEL sel)
{
    mutex_locker_t lock(runtimeLock);
    return getMethod_nolock(cls, sel);
}

static method_t *
getMethod_nolock(Class cls, SEL sel)
{
    method_t *m = nil;

    runtimeLock.assertLocked();

    // fixme nil cls?
    // fixme nil sel?

    ASSERT(cls->isRealized());

    while (cls  &&  ((m = getMethodNoSuper_nolock(cls, sel))) == nil) {
        cls = cls->superclass;
    }

    return m;
}

总结

class_getInstanceMethod：获取实例方法，如果指定的类或其父类不包含带有指定选择器的实例方法，则为NULL

class_getClassMethod：获取类方法，如果指定的类或其父类不包含具有指定选择器的类方法，则为NULL。在这层, 我们不用引入元类判断, 因为在代码层面无法看到元类的实现

class_getMethodImplementation：获取方法的具体实现，如果未查找到，则进行消息转发