宏定义抽取单例

// cmd + n 新建Header File 文件名: Singleton.h

// .h
#define singleton_interface(className) + (instancetype)shared##className;

// .m
// 注意：最后一句不要斜线
#define singleton_implementation(className) static className *_instace; + (id)allocWithZone:(struct _NSZone *)zone {     static dispatch_once_t onceToken;     dispatch_once(&onceToken, ^{         _instace = [super allocWithZone:zone];     });         return _instace; } + (instancetype)shared##className {     if (_instace == nil) {         _instace = [[className alloc] init];     }         return _instace; }