FileChangeMonitor FileChangeMonitor FileChangeMonitor FileChangeMonitor Class


Represents an object that monitors changes to files.

public ref class FileChangeMonitor abstract : System::Runtime::Caching::ChangeMonitor
public abstract class FileChangeMonitor : System.Runtime.Caching.ChangeMonitor
type FileChangeMonitor = class
    inherit ChangeMonitor
Public MustInherit Class FileChangeMonitor
Inherits ChangeMonitor


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 =

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



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

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


        Label1.Text = fileContents;
Imports System.Runtime.Caching
Imports System.IO

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Button1_Click(ByVal sender As Object, _
            ByVal e As System.EventArgs) Handles Button1.Click
        Dim cache As ObjectCache = MemoryCache.Default
        Dim fileContents As String = TryCast(cache("filecontents"), _
        If fileContents Is Nothing Then
            Dim policy As New CacheItemPolicy()
            policy.AbsoluteExpiration = _
            Dim filePaths As New List(Of String)()
            Dim cachedFilePath As String = Server.MapPath("~") & _
            policy.ChangeMonitors.Add(New  _

            ' Fetch the file contents.
            fileContents = File.ReadAllText(cachedFilePath) & _
                vbCrLf & DateTime.Now.ToString()
            cache.Set("filecontents", fileContents, policy)
        End If
        Label1.Text = fileContents
    End Sub

End Class


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.


FileChangeMonitor() FileChangeMonitor() FileChangeMonitor() FileChangeMonitor()

Initializes a new instance of the FileChangeMonitor class. This constructor is called from constructors in derived classes in order to initialize the base class.


FilePaths FilePaths FilePaths FilePaths

Gets a collection that contains the paths of files that are monitored for changes.

HasChanged HasChanged HasChanged HasChanged

Gets a value that indicates that the state that is monitored by the ChangeMonitor class has changed.

(Inherited from ChangeMonitor)
IsDisposed IsDisposed IsDisposed IsDisposed

Gets a value that indicates that the derived instance of a ChangeMonitor class is disposed.

(Inherited from ChangeMonitor)
LastModified LastModified LastModified LastModified

Gets a value that indicates the last time that a file that is being monitored was changed.

UniqueId UniqueId UniqueId UniqueId

Gets a value that represents the ChangeMonitor class instance.

(Inherited from ChangeMonitor)


Dispose() Dispose() Dispose() Dispose()

Releases all resources that are used by the current instance of the ChangeMonitor class.

(Inherited from ChangeMonitor)
Dispose(Boolean) Dispose(Boolean) Dispose(Boolean) Dispose(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)
Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Determines whether the specified object is equal to the current object.

(Inherited from Object)
GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Serves as the default hash function.

(Inherited from Object)
GetType() GetType() GetType() GetType()

Gets the Type of the current instance.

(Inherited from Object)
InitializationComplete() InitializationComplete() InitializationComplete() InitializationComplete()

Called from the constructor of derived classes to indicate that initialization is finished.

(Inherited from ChangeMonitor)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Creates a shallow copy of the current Object.

(Inherited from Object)
NotifyOnChanged(OnChangedCallback) NotifyOnChanged(OnChangedCallback) NotifyOnChanged(OnChangedCallback) NotifyOnChanged(OnChangedCallback)

Called by Cache implementers to register a callback and notify an ObjectCache instance through the OnChangedCallback delegate when a dependency has changed.

(Inherited from ChangeMonitor)
OnChanged(Object) OnChanged(Object) OnChanged(Object) OnChanged(Object)

Called by derived classes to raise the event when a dependency changes.

(Inherited from ChangeMonitor)
ToString() ToString() ToString() ToString()

Returns a string that represents the current object.

(Inherited from Object)

Applies to