Designated initializer : 特定构造方法(方法声明后面带有NS_DESIGNATED_INITIALIZER) 注意:子类如果重写了父类的特定构造方法, 那么必须使用super调用父类的特定构造方法,比如下面的系统构造方法重写时,如果没有调用super则会报错提示: Designated initializer missing a 'super' call to a designated initializer of the super class复制代码

- (instancetype)initWithFrame:(CGRect)frame{   if (self = [super initWithFrame:frame]){        self.titleLabel.font= [UIFontsystemFontOfSize:16];      // 文字颜色        [selfsetTitleColor:[UIColordarkGrayColor] forState:UIControlStateNormal];        [selfsetTitleColor:[UIColorredColor] forState:UIControlStateSelected];    }    returnself;}复制代码

如果不是构造方法,也想让子类重写时不要忘记调用super,则可以使用NS_REQUIRES_SUPER

@interface XMGTest : NSObject//模仿系统方法- (instancetype)initWithName:(NSString *)name NS_DESIGNATED_INITIALIZER;- (instancetype)initWithAge:(NSInteger)age NS_DESIGNATED_INITIALIZER;//自己的方法,提示需要调用super- (void)run NS_REQUIRES_SUPER;@end复制代码