Ivar 详解

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1.Ivar
1.1Ivar 的类型

typedef objc_ivar * Ivar;
  struct objc_ivar {
     char *ivar_name;
     char *ivar_type;
     int ivar_offset;
  #ifdef __LP64__
     int space;
  #endif
  }

Ivar是objc_ivar的指针,包含变量名,变量类型等成员。
1.2为类添加 Ivar
运行时规定,只能在objc_allocateClassPair与objc_registerClassPair两个函数之间为类添加变量

如下所示:


  Class clazz = objc_allocateClassPair(父类class,类名,额外空间);
  
  
  
  
  BOOL flag = class_addIvar(clazz,变量名,变量size,对齐,类型);
  objc_registerClassPair(clazz);

1.3 Ivar的相关操作

 
  const char *ivar_getName(Ivar v);
  
  const char *ivar_getTypeEncoding(Ivar v)
  
  Ivar class_getInstanceVariable(Class cls, const char *name)
  
  Ivar class_getClassVariable(Class cls, const char *name)
  
  Ivar *class_copyIvarList(Class cls, unsigned int *outCount)
  
  id object_getIvar(id obj, Ivar ivar) 
  
  void object_setIvar(id obj, Ivar ivar, id value)

1.4 Ivar的使用


  Class People = objc_allocateClassPair([NSObject class], "People", 0);
  
  BOOL flag1 = class_addIvar(People, "_name", sizeof(NSString*), log2(sizeof(NSString*)), @encode(NSString*));
  if (flag1) {
      NSLog(@"NSString*类型  _name变量添加成功");
  }
  
  BOOL flag2 = class_addIvar(People, "_age", sizeof(int), sizeof(int), @encode(int));
  if (flag2) {
      NSLog(@"int类型 _age变量添加成功");
  }
  
  objc_registerClassPair(People);
  unsigned int varCount;
  
  Ivar * varList = class_copyIvarList(People, &varCount);
  for (int i = 0; i

2 Property
2.1 objc_property_t 与 objc_property_attribute_t类型

typedef struct objc_property *objc_property_t;

  
  typedef struct {
      const char *name;           
      const char *value;          
  } objc_property_attribute_t;

特性相关编码
属性的特性字符串 以 T@encode(type) 开头, 以 V实例变量名称 结尾,中间以特性编码填充,通过property_getAttributes即可查看

特性编码 具体含义

R readonly
C copy
& retain
N nonatomic
G(name) getter=(name)
S(name) setter=(name)
D @dynamic
W weak
P 用于垃圾回收机制

2.2 为类添加Property

 BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)

2.3 Property的相关操作

 
  void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)
  
  objc_property_t class_getProperty(Class cls, const char *name)
  
  objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)
  
  const char *property_getName(objc_property_t property)
  
  const char *property_getAttributes(objc_property_t property) 
  
  objc_property_attribute_t *property_copyAttributeList(objc_property_t property, unsigned int *outCount)
  
  char *property_copyAttributeValue(objc_property_t property, const char *attributeName)

2.4 Property的使用

  Class People = objc_allocateClassPair([NSObject class], "People", 0);
  objc_registerClassPair(People);
  
  objc_property_attribute_t attribute1;
  attribute1.name = "T";
  attribute1.value=@encode(NSString*);
  
  objc_property_attribute_t attribute2 = {"N",""};
  
  objc_property_attribute_t attribute3 = {"C",""};
  
  objc_property_attribute_t attribute4 = {"V","_name"};
  
  objc_property_attribute_t attributes[] ={attribute1,attribute2,attribute3,attribute4};
  
  class_addProperty(People, "name", attributes, 4);
  
  unsigned int propertyCount;
  objc_property_t * properties = class_copyPropertyList(People, &propertyCount);
  for (int i = 0; i

本文转自简书中 ‘Ivar 详解’ 作者:秀才不才 地址:www.jianshu.com/p/ead476cdb…