一：ios 的 isa 的指向

1. isa 的指向如图：

24165805-35d0f6252db8bf96.png

2. 文字表述如下：

实例对象的isa 指向类对象
类对象的isa 指向元类
元类的isa指向 NSObjec 的元类
NSObject 元类指向自己

3.代码验证

定义一个 Person 类

@interface CCPerson : NSObjectend
@implementation CCPerson
@end

打印 isa 指向

    CCPerson *p = [CCPerson alloc];
    Class pClass = object_getClass(p);
    Class pClass1 = object_getClass(pClass);
    Class pClass2 = object_getClass(pClass1);
    NSLog(@"person 类是 %p  元类%p  object 元类 %p",pClass,pClass1,pClass2);
    
    // NSObject实例对象
    NSObject *object1 = [NSObject alloc];
    // NSObject类
    Class class = object_getClass(object1);
    // NSObject元类
    Class metaClass = object_getClass(class);
    // NSObject根元类
    Class rootMetaClass = object_getClass(metaClass);
    // NSObject根根元类
    Class rootRootMetaClass = object_getClass(rootMetaClass);
    NSLog(@"\n%p 实例对象\n%p 类\n%p 元类\n%p 根元类\n%p 根根元类",object1,class,metaClass,rootMetaClass,rootRootMetaClass);
    
    /**
     
     Person 类是 0x100008108  元类0x1000080e0  object 元类 0x7fff991880f0
     0x1005042a0 实例对象
     0x7fff99188118 类
     0x7fff991880f0 元类
     0x7fff991880f0 根元类
     0x7fff991880f0 根根元类
     

4.lldb 调试 验证

如下图，查看源码，获取如何获取isa ，

image.png

联合体中 通过 与 0x00007ffffffffff8 按为与获取

      CCPerson *p = [CCPerson alloc];

     查找CCPersion 的isa
     x/4gx p
     0x10201ce50: 0x001d800100008109 0x0000000000000000
     0x10201ce60: 0x74786554534e5b2d 0x61427265646e6946
     (lldb) p/x  CCPerson.class
     (Class) $7 = 0x0000000100008108 CCPerson
     (lldb) p/x 0x001d800100008109&0x00007ffffffffff8
     (long) $9 = 0x0000000100008108
     
     
    
     继续查找 
     
     x/4gx 0x0000000100008108
     0x100008108: 0x00000001000080e0 0x00007fff99188118
     0x100008118: 0x0000000102304080 0x0001801000000003
     (lldb) p/x 0x00000001000080e0&0x00007ffffffffff8
     (long) $11 = 0x00000001000080e0
     (lldb) po 0x00000001000080e0
     CCPerson
     
     
     x/4gx 0x00000001000080e0
     0x1000080e0: 0x00007fff991880f0 0x00007fff991880f0
     0x1000080f0: 0x00000001004715d0 0x0004e03100000007
     (lldb) p/x 0x00007fff991880f0&0x00007ffffffffff8
     (long) $13 = 0x00007fff991880f0
     (lldb) po $13
     NSObject
     
     
     x/4gx $13
     0x7fff991880f0: 0x00007fff991880f0 0x00007fff99188118
     0x7fff99188100: 0x00000001006072b0 0x0004e03100000007
     (lldb) p/x 0x00007fff991880f0&0x00007ffffffffff8
     (long) $14 = 0x00007fff991880f0
     (lldb) po $14
     NSObject
     
     
     x/4gx NSObject.class
     0x7fff99188118: 0x00007fff991880f0 0x0000000000000000
     0x7fff99188128: 0x00000001020231b0 0x0002801000000003
     (lldb) p/x  0x00007fff991880f0&0x00007ffffffffff8
     (long) $17 = 0x00007fff991880f0
     
     
     */