FileChangeMonitor Class

Represents an object that monitors changes to files.

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

public abstract class FileChangeMonitor : ChangeMonitor

The FileChangeMonitor type exposes the following members.

  NameDescription
Protected methodFileChangeMonitorInitializes a new instance of the FileChangeMonitor class. This constructor is called from constructors in derived classes in order to initialize the base class.
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  NameDescription
Public propertyFilePathsGets a collection that contains the paths of files that are monitored for changes.
Public propertyHasChangedGets a value that indicates that the state that is monitored by the ChangeMonitor class has changed. (Inherited from ChangeMonitor.)
Public propertyIsDisposedGets a value that indicates that the derived instance of a ChangeMonitor class is disposed. (Inherited from ChangeMonitor.)
Public propertyLastModifiedGets a value that indicates the last time that a file that is being monitored was changed.
Public propertyUniqueIdGets a value that represents the ChangeMonitor class instance. (Inherited from ChangeMonitor.)
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  NameDescription
Public methodDispose()Releases all resources that are used by the current instance of the ChangeMonitor class. (Inherited from ChangeMonitor.)
Protected methodDispose(Boolean)Releases all managed and unmanaged resources and any references to the ChangeMonitor instance. This overload must be implemented by derived change-monitor classes. (Inherited from ChangeMonitor.)
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.)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodInitializationCompleteCalled from the constructor of derived classes to indicate that initialization is finished. (Inherited from ChangeMonitor.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodNotifyOnChangedCalled by Cache implementers to register a callback and notify an ObjectCache instance through the OnChangedCallback delegate when a dependency has changed. (Inherited from ChangeMonitor.)
Protected methodOnChangedCalled by derived classes to raise the event when a dependency changes. (Inherited from ChangeMonitor.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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The FileChangeMonitor class is a base ChangeMonitor type for classes that monitor changes to files. To create a monitor for changes in the file system, you can inherit from this class.

Notes to Inheritors

For information about the inheritance contract that must be followed, see the Notes for Inheritors section in the ChangeMonitor class overview.

The following example shows how to create a cache item that uses a HostFileChangeMonitor object to monitor the state of the source data (a file) on the file system. The HostFileChangeMonitor class inherits from the FileChangeMonitor class. The cache entry is defined using a CacheItemPolicy object that provides eviction and expiration details for the cache entry.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Runtime.Caching;
using System.IO;

public partial class _Default : System.Web.UI.Page
{


    protected void Button1_Click1(object sender, EventArgs e)
    {
        ObjectCache cache = MemoryCache.Default;
        string fileContents = cache["filecontents"] as string;

        if (fileContents == null)
        {
            CacheItemPolicy policy = new CacheItemPolicy();
            policy.AbsoluteExpiration =
                DateTimeOffset.Now.AddSeconds(10.0);

            List<string> filePaths = new List<string>();
            string cachedFilePath = Server.MapPath("~") +
                "\\cacheText.txt";

            filePaths.Add(cachedFilePath);

            policy.ChangeMonitors.Add(new
                HostFileChangeMonitor(filePaths));

            // Fetch the file contents.
            fileContents = File.ReadAllText(cachedFilePath) + "\n"
                + DateTime.Now.ToString();

            cache.Set("filecontents", fileContents, policy);

        }

        Label1.Text = fileContents;
    }
}

.NET Framework

Supported in: 4.5, 4

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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