首先创建一个继承自NSObject的类，我的叫MyOrder；
然后在.h文件中写
+ (instancetype)shareMyOrder;
.m文件中这样写：
+ (MyOrder *)shareMyOrder{
static MyOrder *_order = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken,^{
_order = [[MyOrder alloc] init];
});
return _order;
}
OK
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