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CacheItemUpdateCallback Delegate

Defines a callback method for notifying applications before a cached item is removed from the cache.

Namespace:  System.Web.Caching
Assembly:  System.Web (in System.Web.dll)

public delegate void CacheItemUpdateCallback(
	string key,
	CacheItemUpdateReason reason,
	out Object expensiveObject,
	out CacheDependency dependency,
	out DateTime absoluteExpiration,
	out TimeSpan slidingExpiration
)

Parameters

key
Type: System.String

The identifier of the item that is being removed from the cache.

reason
Type: System.Web.Caching.CacheItemUpdateReason

The reason that the item is being removed from the cache.

expensiveObject
Type: System.Object

When this method returns, contains the cached item object that contains the updates.

dependency
Type: System.Web.Caching.CacheDependency

When this method returns, contains the object that defines the dependency between the item object and a file, a cache key, an array of either, or another CacheDependency object.

absoluteExpiration
Type: System.DateTime

When this method returns, contains the time at which the object expired.

slidingExpiration
Type: System.TimeSpan

When this method returns, contains the interval between the time that the object was last accessed and the time at which the object expired.

When an object expires in the cache, ASP.NET calls the CacheItemUpdateCallback method with the key for the cache item and the reason you might want to update the item. The remaining parameters of this method are out parameters. You supply the new cached item and optional expiration and dependency values to use when refreshing the cached item.

The update callback is not called if the cached item is explicitly removed by using a call to Remove.

If you want the cached item to be removed from the cache, you must return null in the expensiveObject parameter. Otherwise, you return a reference to the new cached data by using the expensiveObject parameter. If you do not specify expiration or dependency values, the item will be removed from the cache only when memory is needed.

If the callback method throws an exception, ASP.NET suppresses the exception and removes the cached value.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5 SP1, 3.0 SP2, 2.0 SP2
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