單例的定義

在.h 文件中定義：

+(instancetype) alloc __attribute__((unavailable("alloc not available, call sharedInstance instead")));
-(instancetype) init __attribute__((unavailable("init not available, call sharedInstance instead")));
+(instancetype) new __attribute__((unavailable("new not available, call sharedInstance instead")));

 

在.m 文件中定義：

+ (instancetype)sharedInstance {
   
    static id shared = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        shared = [[super alloc] initUniqueInstance];
    });
   
    return shared;
}

-(instancetype)initUniqueInstance {
   
    self = [super init];
    if (self) {
       
        [self customInit];
    }
    return self;
}

- (void)customInit {
   
   
}