iOS runtime探究(三): 从runtime开始理解OC的属性property你要知道的runtime都在这里

//OC自定义类的定义
@interface Person : NSObject

@property (nonatomic, copy) NSString* cjmName;
@property (nonatomic, assign) NSUInteger cjmAge;

@end

@implementation Person

@synthesize cjmName = _cjmName;
@synthesize cjmAge = _cjmAge;

@end


//clang转写为.cpp的相关代码
struct _prop_t {
        const char *name;
        const char *attributes;
};

static struct /*_prop_list_t*/ {
        unsigned int entsize;  // sizeof(struct _prop_t)
        unsigned int count_of_properties;
        struct _prop_t prop_list[2];
} _OBJC_$_PROP_LIST_Person __attribute__ ((used, section ("__DATA,__objc_const"))) = {
        sizeof(_prop_t),
        2,
        {{"cjmName","T@\"NSString\",C,N,V_cjmName"},
        {"cjmAge","TQ,N,V_cjmAge"}}
};

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person* p = [[Person alloc] init];
        p.cjmName = @"Jiaming Chen";
        
        unsigned int propertyCount = 0;
        objc_property_t *propertyList = class_copyPropertyList([p class], &propertyCount);
        for (int i = 0; i < propertyCount; i++) {
            const char* name = property_getName(propertyList[i]);
            const char* attributes = property_getAttributes(propertyList[i]);
            NSLog(@"%s %s", name, attributes);
        }
    }
    return 0;
}

typedef struct objc_property *objc_property_t;

/** 
 * Describes the properties declared by a class.
 * 
 * @param cls The class you want to inspect.
 * @param outCount On return, contains the length of the returned array. 
 *  If \e outCount is \c NULL, the length is not returned.        
 * 
 * @return An array of pointers of type \c objc_property_t describing the properties 
 *  declared by the class. Any properties declared by superclasses are not included. 
 *  The array contains \c *outCount pointers followed by a \c NULL terminator. You must free the array with \c free().
 * 
 *  If \e cls declares no properties, or \e cls is \c Nil, returns \c NULL and \c *outCount is \c 0.
 */
OBJC_EXPORT objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)
    OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);

2017-03-27 09:59:20.914487 OCTest[2467:460742] cjmName T@"NSString",C,N,V_cjmName
2017-03-27 09:59:20.915321 OCTest[2467:460742] cjmAge TQ,N,V_cjmAge

/** 
 * Returns a property with a given name of a given class.
 * 
 * @param cls The class you want to inspect.
 * @param name The name of the property you want to inspect.
 * 
 * @return A pointer of type \c objc_property_t describing the property, or
 *  \c NULL if the class does not declare a property with that name, 
 *  or \c NULL if \e cls is \c Nil.
 */
OBJC_EXPORT objc_property_t class_getProperty(Class cls, const char *name)
    OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
    
/** 
 * Adds a property to a class.
 * 
 * @param cls The class to modify.
 * @param name The name of the property.
 * @param attributes An array of property attributes.
 * @param attributeCount The number of attributes in \e attributes.
 * 
 * @return \c YES if the property was added successfully, otherwise \c NO
 *  (for example, the class already has that property).
 */
OBJC_EXPORT BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)
    OBJC_AVAILABLE(10.7, 4.3, 9.0, 1.0);

/** 
 * Replace a property of a class. 
 * 
 * @param cls The class to modify.
 * @param name The name of the property.
 * @param attributes An array of property attributes.
 * @param attributeCount The number of attributes in \e attributes. 
 */
OBJC_EXPORT void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)
    OBJC_AVAILABLE(10.7, 4.3, 9.0, 1.0);

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person* p = [[Person alloc] init];
        p.cjmAge = 20;
        p.cjmName = @"Jiaming Chen";
        
        unsigned int propertyCount = 0;
        objc_property_t *propertyList = class_copyPropertyList([p class], &propertyCount);
        for (int i = 0; i < propertyCount; i++) {
            const char* name = property_getName(propertyList[i]);
            const char* attributes = property_getAttributes(propertyList[i]);
            NSLog(@"%s %s", name, attributes);
        }
        objc_property_attribute_t attributes = {
            "T@\"NSString\",C,N,V_studentIdentifier",
            "",
        };
        class_addProperty([p class], "studentIdentifier", &attributes, 1);
        objc_property_t property = class_getProperty([p class], "studentIdentifier");
        NSLog(@"%s %s", property_getName(property), property_getAttributes(property));
    }
    return 0;
}