runtime——Class——属性

objc_property_t

/// An opaque type that represents an Objective-C declared property.typedef struct objc_property *objc_property_t;/// Defines a property attributetypedef struct {    const char *name;           /**< The name of the attribute */    const char *value;          /**< The value of the attribute (usually empty) */} objc_property_attribute_t;

OBJC_EXPORT const char *property_getName(objc_property_t property)      __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);OBJC_EXPORT const char *property_getAttributes(objc_property_t property)      __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);OBJC_EXPORT char *property_copyAttributeValue(objc_property_t property, const char *attributeName)     __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);OBJC_EXPORT objc_property_attribute_t *property_copyAttributeList(objc_property_t property, unsigned int *outCount)     __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);

objc_property_t应用

@interface FBAnimal : NSObject@property (nonatomic, assign) int age;@property (nonatomic, strong) UIColor *color;@end@implementation FBAnimal@end

- (void)use_property{    objc_property_t age = class_getProperty([FBAnimal class], "age");    objc_property_t color = class_getProperty([FBAnimal class], "color");    NSLog(@"propertyName = %s, propertyAttr = %s", property_getName(age), property_getAttributes(age));    NSLog(@"propertyName = %s, propertyAttr = %s", property_getName(color), property_getAttributes(color));        NSLog(@"age property attr list:");    unsigned int ageAttrCnt = 0;    objc_property_attribute_t* ageAttrList = property_copyAttributeList(age, &ageAttrCnt);    for(int i = 0; i < ageAttrCnt; ++i)    {        objc_property_attribute_t thisAttr = ageAttrList[i];        NSLog(@"attr name = %s, attr value = %s", thisAttr.name, thisAttr.value);    }    free(ageAttrList);        NSLog(@"color property attr list:");    unsigned int colorAttrCnt = 0;    objc_property_attribute_t* colorAttrList = property_copyAttributeList(color, &colorAttrCnt);    for(int i = 0; i < colorAttrCnt; ++i)    {        objc_property_attribute_t thisAttr = colorAttrList[i];        NSLog(@"attr name = %s, attr value = %s", thisAttr.name, thisAttr.value);    }    free(colorAttrList);}

output：

propertyName = age, propertyAttr = Ti,N,V_agepropertyName = color, propertyAttr = T@"UIColor",&,N,V_colorage property attr list:attr name = T, attr value = iattr name = N, attr value = attr name = V, attr value = _agecolor property attr list:attr name = T, attr value = @"UIColor"attr name = &, attr value = attr name = N, attr value = attr name = V, attr value = _color

objc_property_t总结

• property的attribute包括property类型(T)，property对应数据成员(V)，property原子操作性(N表示nonatomic)，property内存方式(&表示strong)

api

OBJC_EXPORT objc_property_t class_getProperty(Class cls, const char *name)     __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);OBJC_EXPORT objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)     __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);OBJC_EXPORT BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)     __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);OBJC_EXPORT void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)     __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);

应用

@interface FBAnimal : NSObject@property (nonatomic, assign) int age;@property (nonatomic, strong) UIColor *color;@end@interface FBAnimal ()@property (nonatomic, assign) int food1;@property (nonatomic, assign) int food2;@end@interface FBAnimal ()@property (nonatomic, assign) int food3;@end@implementation FBAnimal@end@interface FBDog : FBAnimal@property (nonatomic, strong) NSString *country;@end@implementation FBDog@end

- (void)class_property{    NSLog(@"animal property list:");    unsigned int animalPropertyCnt = 0;    objc_property_t* animalPropertyList = class_copyPropertyList([FBAnimal class], &animalPropertyCnt);    for(int i = 0; i < animalPropertyCnt; i++)    {        objc_property_t thisProperty = animalPropertyList[i];        NSLog(@"propertyName = %s, propertyAttr = %s", property_getName(thisProperty), property_getAttributes(thisProperty));    }    free(animalPropertyList);        NSLog(@"dog property list:");    unsigned int dogPropertyCnt = 0;    objc_property_t* dogPropertyList = class_copyPropertyList([FBDog class], &dogPropertyCnt);    for(int i = 0; i < dogPropertyCnt; i++)    {        objc_property_t thisProperty = dogPropertyList[i];        NSLog(@"propertyName = %s, propertyAttr = %s", property_getName(thisProperty), property_getAttributes(thisProperty));    }    free(dogPropertyList);}

output：

animal property list:propertyName = food3, propertyAttr = Ti,N,V_food3propertyName = food1, propertyAttr = Ti,N,V_food1propertyName = food2, propertyAttr = Ti,N,V_food2propertyName = age, propertyAttr = Ti,N,V_agepropertyName = color, propertyAttr = T@"UIColor",&,N,V_colordog property list:propertyName = country, propertyAttr = T@"NSString",&,N,V_country

总结

• 如果类中已含对应name的property(包含super_class)，class_addProperty不会添加到当前类中
• 如果类中已含对应name的property，进行替换，如果类中不含对应name的Property，class_replaceProperty等同于class_addProperty
• class_getProperty包含super_class
• class_copyProperty不包含super_class
• 同一类property排列顺序：extension interface->primary class interface
• 同一类多个extension property排列顺序：按extension interface定义顺序逆序排列，即先定义extension interface排后面，后定义extension interface排前面
• 同一interface(primary class interface，extension interface)的property排列顺序：按property定义顺序排列，即先定义property排前面，后定义property排后面