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CacheDependency Class

Establishes a dependency relationship between an item stored in an ASP.NET application's Cache object and a file, cache key, an array of either, or another CacheDependency object. The CacheDependency class monitors the dependency relationships so that when any of them changes, the cached item will be automatically removed.

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

public class CacheDependency : IDisposable

The CacheDependency type exposes the following members.

  NameDescription
Protected methodCacheDependency()Initializes a new instance of the CacheDependency class.
Public methodCacheDependency(String)Initializes a new instance of the CacheDependency class that monitors a file or directory for changes.
Public methodCacheDependency(String[])Initializes a new instance of the CacheDependency class that monitors an array of paths (to files or directories) for changes.
Public methodCacheDependency(String, DateTime)Initializes a new instance of the CacheDependency class that monitors a file or directory for changes.
Public methodCacheDependency(String[], DateTime)Initializes a new instance of the CacheDependency class that monitors an array of paths (to files or directories) for changes and specifies a time when change monitoring begins.
Public methodCacheDependency(String[], String[])Initializes a new instance of the CacheDependency class that monitors an array of paths (to files or directories), an array of cache keys, or both for changes.
Public methodCacheDependency(String[], String[], DateTime)Initializes a new instance of the CacheDependency class that monitors an array of paths (to files or directories), an array of cache keys, or both for changes.
Public methodCacheDependency(String[], String[], CacheDependency)Initializes a new instance of the CacheDependency class that monitors an array of paths (to files or directories), an array of cache keys, or both for changes. It also makes itself dependent upon a separate instance of the CacheDependency class.
Public methodCacheDependency(String[], String[], CacheDependency, DateTime)Initializes a new instance of the CacheDependency class that monitors an array of paths (to files or directories), an array of cache keys, or both for changes. It also makes itself dependent upon another instance of the CacheDependency class and a time when the change monitoring begins.
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  NameDescription
Public propertyHasChangedGets a value indicating whether the CacheDependency object has changed.
Public propertyUtcLastModifiedGets the time when the dependency was last changed.
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  NameDescription
Protected methodDependencyDisposeReleases the resources used by the CacheDependency class and any classes that derive from CacheDependency.
Public methodDisposeReleases the resources used by the CacheDependency object.
Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Protected methodFinishInitCompletes initialization of the CacheDependency object.
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetUniqueIDRetrieves a unique identifier for a CacheDependency object.
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodNotifyDependencyChangedNotifies the base CacheDependency object that the dependency represented by a derived CacheDependency class has changed.
Protected methodSetUtcLastModifiedMarks the time when a dependency last changed.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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If you add an item to the cache that is dependent on another object, such as a file or array of files, the dependent item is automatically removed from the cache when the object changes. For example, suppose you create a DataSet object based on data in an XML file. You can add the DataSet to the cache with a CacheDependency object that makes the DataSet dependent on the XML file. If the XML file changes, the DataSet is removed from the cache.

You can add items with dependencies to your application's cache with the Add and Cache.Insert methods. You cannot use the Item property to add items to the cache with dependencies.

To set up a dependency, you create an instance of the CacheDependency class, specifying the files, keys, or directories on which the item is dependent, and then pass the dependency to the Add or Cache.Insert method. The CacheDependency instance can represent a single file or directory, an array of files or directories, or an array of files or directories along with an array of cache keys (these represent other items stored in the Cache object).

The following code example demonstrates using the HasChanged property to determine whether a CacheDependency changed since the previous request for an item in the Cache. The dt value passed in the start parameter is set to DateTime.Now.

// Insert the cache item.
CacheDependency dep = new CacheDependency(fileName, dt);
cache.Insert("key", "value", dep);

// Check whether CacheDependency.HasChanged is true.
if (dep.HasChanged)
  Response.Write("<p>The dependency has changed.");  
else Response.Write("<p>The dependency has not changed.");

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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