在.h 文件中定义：

+(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 文件中定义：

+ (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 {      }