isa指针
消息机制
对象方法存储在类对象中,所以调用对象方法是在实例对象的isa指向类对象,让类对象调用对象方法.很方便的通过实例对象的isa找到类对象,也可以通过类对象的isa找到元类对象来完成方法的调用
类方法在元类对象中,类对象的isa指向它的元类对象
superclass
总结:
![这里写图片描述](https://img-blog.csdn.net/20180724140242100?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTI1ODE3NjA=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70)
//
// MJClassInfo.h
// TestClass
//
// Created by MJ Lee on 2018/3/8.
// Copyright © 2018年 MJ Lee. All rights reserved.
//
#import <Foundation/Foundation.h>
#ifndef MJClassInfo_h
#define MJClassInfo_h
# if __arm64__
# define ISA_MASK 0x0000000ffffffff8ULL
# elif __x86_64__
# define ISA_MASK 0x00007ffffffffff8ULL
# endif
#if __LP64__
typedef uint32_t mask_t;
#else
typedef uint16_t mask_t;
#endif
typedef uintptr_t cache_key_t;
struct bucket_t {
cache_key_t _key;
IMP _imp;
};
struct cache_t {
bucket_t *_buckets;
mask_t _mask;
mask_t _occupied;
};
struct entsize_list_tt {
uint32_t entsizeAndFlags;
uint32_t count;
};
struct method_t {
SEL name;
const char *types;
IMP imp;
};
struct method_list_t : entsize_list_tt {
method_t first;
};
struct ivar_t {
int32_t *offset;
const char *name;
const char *type;
uint32_t alignment_raw;
uint32_t size;
};
struct ivar_list_t : entsize_list_tt {
ivar_t first;
};
struct property_t {
const char *name;
const char *attributes;
};
struct property_list_t : entsize_list_tt {
property_t first;
};
struct chained_property_list {
chained_property_list *next;
uint32_t count;
property_t list[0];
};
typedef uintptr_t protocol_ref_t;
struct protocol_list_t {
uintptr_t count;
protocol_ref_t list[0];
};
struct class_ro_t {
uint32_t flags;
uint32_t instanceStart;
uint32_t instanceSize; // instance对象占用的内存空间
#ifdef __LP64__
uint32_t reserved;
#endif
const uint8_t * ivarLayout;
const char * name; // 类名
method_list_t * baseMethodList;
protocol_list_t * baseProtocols;
const ivar_list_t * ivars; // 成员变量列表
const uint8_t * weakIvarLayout;
property_list_t *baseProperties;
};
struct class_rw_t {
uint32_t flags;
uint32_t version;
const class_ro_t *ro;
method_list_t * methods; // 方法列表
property_list_t *properties; // 属性列表
const protocol_list_t * protocols; // 协议列表
Class firstSubclass;
Class nextSiblingClass;
char *demangledName;
};
#define FAST_DATA_MASK 0x00007ffffffffff8UL
struct class_data_bits_t {
uintptr_t bits;
public:
class_rw_t* data() {
return (class_rw_t *)(bits & FAST_DATA_MASK);
}
};
/* OC对象 */
struct mj_objc_object {
void *isa;
};
/* 类对象 */
struct mj_objc_class : mj_objc_object {
Class superclass;
cache_t cache;
class_data_bits_t bits;
public:
class_rw_t* data() {
return bits.data();
}
mj_objc_class* metaClass() {
return (mj_objc_class *)((long long)isa & ISA_MASK);
}
};
#endif /* MJClassInfo_h */
//
// main.m
// Interview04-class的结构
//
// Created by MJ Lee on 2018/4/15.
// Copyright © 2018年 MJ Lee. All rights reserved.
//
// objective-c++
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import "MJClassInfo.h"
// MJPerson
@interface MJPerson : NSObject <NSCopying>
{
@public
int _age;
}
@property (nonatomic, assign) int no;
- (void)personInstanceMethod;
+ (void)personClassMethod;
@end
@implementation MJPerson
- (void)test
{
}
- (void)personInstanceMethod
{
}
+ (void)personClassMethod
{
}
- (id)copyWithZone:(NSZone *)zone
{
return nil;
}
@end
// MJStudent
@interface MJStudent : MJPerson <NSCoding>
{
@public
int _weight;
}
@property (nonatomic, assign) int height;
- (void)studentInstanceMethod;
+ (void)studentClassMethod;
@end
@implementation MJStudent
- (void)test
{
}
- (void)studentInstanceMethod
{
}
+ (void)studentClassMethod
{
}
- (id)initWithCoder:(NSCoder *)aDecoder
{
return nil;
}
- (void)encodeWithCoder:(NSCoder *)aCoder
{
}
@end
int main(int argc, const char * argv[]) {
@autoreleasepool {
MJStudent *stu = [[MJStudent alloc] init];
stu->_weight = 10;
mj_objc_class *studentClass = (__bridge mj_objc_class *)([MJStudent class]);
mj_objc_class *personClass = (__bridge mj_objc_class *)([MJPerson class]);
class_rw_t *studentClassData = studentClass->data();
class_rw_t *personClassData = personClass->data();
class_rw_t *studentMetaClassData = studentClass->metaClass()->data();
class_rw_t *personMetaClassData = personClass->metaClass()->data();
NSLog(@"1111");
}
return 0;
}