Cache在System.Web.Cacheing命名空间中定义，它是一种key/value的object。类似Session Objcet和application Object，ViewState Object都可以当作Cache来使用。但是Cache在.net 中还有其它很多特性，例如依赖属性和自动过期的一些策略等。我们先用一些简单的示例来了解Cache的概念。
（1）最简单的Cache的使用：
Cache[
"
Time
"
]
=
DateTime.Now.ToString();
lblCacheTime.Text = Cache[ " Time " ].ToString()
Cache.Remove( " Time " );
lblCacheTime.Text = Cache[ " Time " ].ToString()
Cache.Remove( " Time " );
（2）：基于硬盘上的文件变化的一种Cache的过期策略
CacheDependency dependucy = new CacheDependency(“customdatasource.xml");
Cache.Insert("Time", strDateTime, dependucy);
当CustomDataSource.xml中的内容发生变化时Cache中Time为Key的缓存就会被移除。当然我们还基于一批文件。CacheDependency这个类中提供很多构造函数，有兴趣的朋友可以去查一下MSDN。
（3）：基于其它缓存的Key的一种Cache过期策略
代码
//
Create a cache entry.
Cache[ " key1 " ] = " Value 1 " ;
// Make key2 dependent on key1.
String[] dependencyKey = new String[ 1 ];
dependencyKey[ 0 ] = " key1 " ;
CacheDependency dependency = new CacheDependency( null , dependencyKey);
Cache.Insert( " key2 " , " Value 2 " , dependency);
Cache[ " key1 " ] = " Value 1 " ;
// Make key2 dependent on key1.
String[] dependencyKey = new String[ 1 ];
dependencyKey[ 0 ] = " key1 " ;
CacheDependency dependency = new CacheDependency( null , dependencyKey);
Cache.Insert( " key2 " , " Value 2 " , dependency);
（4）：基于相对时间和绝对时间的一种Cache过期策略
代码
///
Absolute expiration
Cache.Insert( " CachedItem " , item, null , DateTime.Now.AddSeconds( 5 ),
Cache.NoSlidingExpiration);
/// Sliding expiration
Cache.Insert( " CachedItem " , item, null , Cache.NoAbsoluteExpiration,
TimeSpan.FromSeconds( 5 ));
Cache.Insert( " CachedItem " , item, null , DateTime.Now.AddSeconds( 5 ),
Cache.NoSlidingExpiration);
/// Sliding expiration
Cache.Insert( " CachedItem " , item, null , Cache.NoAbsoluteExpiration,
TimeSpan.FromSeconds( 5 ));
（5）当Cache过期时被执行的时候，还可以执行一些函数，来做一些工作。
代码
CacheItemRemovedCallback onRemove
=
new
CacheItemRemovedCallback( this .RemovedCallback);
Cache.Insert( " CachedItem " ,
item,
null ,
Cache.NoAbsoluteExpiration,
Cache.NoSlidingExpiration,
CacheItemPriority.Default,
onRemove);
// Implement the function to handle the expiration of the cache.
public void RemovedCallback( string key, object value, CacheItemRemovedReason r)
{
// Test whether the item is expired, and reinsert it into the cache.
if (r == CacheItemRemovedReason.Expired)
{
// Reinsert it into the cache again.
CacheItemRemovedCallback onRemove = null ;
onRemove = new CacheItemRemovedCallback( this .RemovedCallback);
Cache.Insert(key,
value,
null ,
Cache.NoAbsoluteExpiration,
Cache.NoSlidingExpiration,
CacheItemPriority.Default,
onRemove);
}
}
CacheItemRemovedCallback( this .RemovedCallback);
Cache.Insert( " CachedItem " ,
item,
null ,
Cache.NoAbsoluteExpiration,
Cache.NoSlidingExpiration,
CacheItemPriority.Default,
onRemove);
// Implement the function to handle the expiration of the cache.
public void RemovedCallback( string key, object value, CacheItemRemovedReason r)
{
// Test whether the item is expired, and reinsert it into the cache.
if (r == CacheItemRemovedReason.Expired)
{
// Reinsert it into the cache again.
CacheItemRemovedCallback onRemove = null ;
onRemove = new CacheItemRemovedCallback( this .RemovedCallback);
Cache.Insert(key,
value,
null ,
Cache.NoAbsoluteExpiration,
Cache.NoSlidingExpiration,
CacheItemPriority.Default,
onRemove);
}
}