Cache dependencies allow the validity of a cache item to be based on a file or directory on the web server, or on another cache item. When the dependency object changes, the dependent cache item is invalidated and removed automatically. To set up a dependency, you first create a CacheDependency object that references the file, directory, or cache item upon which the dependency will be based. You then use the Cache.Insert( ) method to add the dependent cache item, with the CacheDependency object supplied as a parameter.
The overloaded constructor of the CacheDependency class determines the type of dependency. You can pass a single string argument to set up a dependency on a file or directory (CacheDependency(Server.MapPath("data.xml")) or you can use a second string argument with the key of another cache item (CacheDependency(Nothing, "MyData")). Other versions of the constructor allow you to specify an array of strings specifying files or cache objects. If any one file or object changes, the dependent cache item will be invalidated.
The CacheDependency object begins to monitor for changes as soon as it is created to account for changes that may occur in the brief delay before the dependent cache item is added to the Cache class.
public sealed class CacheDependency : IDisposable { // Public Constructors public CacheDependency(string filename); public CacheDependency(string[ ] filenames); public CacheDependency(string[ ] filenames, DateTime start); public CacheDependency(string[ ] filenames, string[ ] cachekeys); public CacheDependency(string[ ] filenames, string[ ] cachekeys, CacheDependency dependency); public CacheDependency(string[ ] filenames, string[ ] cachekeys, CacheDependency dependency, DateTime start); public CacheDependency(string[ ] filenames, string[ ] cachekeys, DateTime start); public CacheDependency(string filename, DateTime start); // Public Instance Properties public bool HasChanged{get; } // Public Instance Methods public void Dispose( ); // implements IDisposable }
