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Cache.Add Method

Adds the specified item to the Cache object with dependencies, expiration and priority policies, and a delegate you can use to notify your application when the inserted item is removed from the Cache.

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

public Object Add(
	string key,
	Object value,
	CacheDependency dependencies,
	DateTime absoluteExpiration,
	TimeSpan slidingExpiration,
	CacheItemPriority priority,
	CacheItemRemovedCallback onRemoveCallback


Type: System.String
The cache key used to reference the item.
Type: System.Object
The item to be added to the cache.
Type: System.Web.Caching.CacheDependency
The file or cache key dependencies for the item. When any dependency changes, the object becomes invalid and is removed from the cache. If there are no dependencies, this parameter contains null.
Type: System.DateTime
The time at which the added object expires and is removed from the cache. If you are using sliding expiration, the absoluteExpiration parameter must be NoAbsoluteExpiration.
Type: System.TimeSpan
The interval between the time the added object was last accessed and the time at which that object expires. If this value is the equivalent of 20 minutes, the object expires and is removed from the cache 20 minutes after it is last accessed. If you are using absolute expiration, the slidingExpiration parameter must be NoSlidingExpiration.
Type: System.Web.Caching.CacheItemPriority
The relative cost of the object, as expressed by the CacheItemPriority enumeration. The cache uses this value when it evicts objects; objects with a lower cost are removed from the cache before objects with a higher cost.
Type: System.Web.Caching.CacheItemRemovedCallback
A delegate that, if provided, is called when an object is removed from the cache. You can use this to notify applications when their objects are deleted from the cache.

Return Value

Type: System.Object
An object that represents the item that was added if the item was previously stored in the cache; otherwise, null.


The key or value parameter is set to null.


The slidingExpiration parameter is set to less than TimeSpan.Zero or more than one year.


The absoluteExpiration and slidingExpiration parameters are both set for the item you are trying to add to the Cache.

Calls to this method will fail if an item with the same key parameter is already stored in the Cache. To overwrite an existing Cache item using the same key parameter, use the Insert method.

You cannot set both the absoluteExpiration and slidingExpiration parameters. If you intend the cache item to expire at a specific time, you set the absoluteExpiration parameter to the specific time, and the slidingExpiration parameter to NoSlidingExpiration.

If you intend the cache item to expire after a certain amount of time has passed since the item was last accessed, you set the slidingExpiration parameter to the expiration interval, and the absoluteExpiration parameter to NoAbsoluteExpiration.

The following example creates an AddItemToCache method. When this method is called, it sets an itemRemoved property to false and registers an onRemove method with a new instance of the CacheItemRemovedCallback delegate. The delegate's signature is used in the RemovedCallback method. The AddItemToCache method then checks the value associated with the Key1 key in the cache. If the value is null, the Add method places an item in the cache with a key of Key1, a value of Value 1, an absolute expiration of 60 seconds, and a high cache priority. It also uses the onRemove method as an argument. This allows the RemovedCallback method to be called when this item is removed from the cache.


For examples of how to use the CacheDependency class and the CacheItemRemovedCallback delegate, see Caching Application Data.

public void AddItemToCache(Object sender, EventArgs e) {
    itemRemoved = false;

    onRemove = new CacheItemRemovedCallback(this.RemovedCallback);

    if (Cache["Key1"] == null)
      Cache.Add("Key1", "Value 1", null, DateTime.Now.AddSeconds(60), Cache.NoSlidingExpiration, CacheItemPriority.High, onRemove);

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.