NoAbsoluteExpiration用错了?

Question

HttpContext.Current.Cache.Insert("user",ds,null,System.Web.Cache.NoAbsoluteExpiration,TimeSpan.Zero,CacheItemPriority.Default,new CacheItemRemovedCallback(onmove));
类型或命名空间名称“Cache”在类或命名空间“System.Web”中不存在(是否缺少程序集引用？)
这问题如何解决,HttpContext.Current.Cache.Insert("user",ds,null,System.Web.Cache.NoAbsoluteExpiration,TimeSpan.Zero,CacheItemPriority.Default,new CacheItemRemovedCallback(onmove));
这句是在一个类的构造函数里!

Answer 1

HttpContext.Current.Cache.Insert("user",ds,null,System.Web.Cache.NoAbsoluteExpiration,TimeSpan.Zero,CacheItemPriority.Default,new CacheItemRemovedCallback(onmove));
改成
HttpContext.Current.Cache.Insert("user",ds,null,System.Web.Caching.Cache.NoAbsoluteExpiration,TimeSpan.Zero,CacheItemPriority.Default,new CacheItemRemovedCallback(onmove));

Answer 2

System.Web.Cache.NoAbsoluteExpiration
========>
System.Web.Caching.Cache.NoAbsoluteExpiration