KVC

 赋值

// 能修改私有成员变量

- (void)setValue:(id)value forKey:(NSString *)key;

- (void)setValue:(id)value forKeyPath:(NSString *)keyPath;

- (void)setValuesForKeysWithDictionary:(NSDictionary *)keyedValues;

取值

// 能取得私有成员变量的值

- (id)valueForKey:(NSString *)key;

- (id)valueForKeyPath:(NSString *)keyPath;

- (NSDictionary *)dictionaryWithValuesForKeys:(NSArray *)keys;

KVC最重要的作用就是修改私有变量。