Defines a callback method for notifying applications when a cached item is removed from the Cache.
(in System.Web.dll)
Visual Basic (Declaration)
Public Delegate Sub CacheItemRemovedCallback ( _
key As String, _
value As Object, _
reason As CacheItemRemovedReason _
)
Dim instance As New CacheItemRemovedCallback(AddressOf HandlerMethod)
public delegate void CacheItemRemovedCallback(
string key,
Object value,
CacheItemRemovedReason reason
)
public delegate void CacheItemRemovedCallback(
String^ key,
Object^ value,
CacheItemRemovedReason reason
)
JScript does not support delegates.
The following code example demonstrates a page that shows users the value assigned to an item in the cache and then notifies them when the item is removed from the cache. It creates a RemovedCallback method, which uses the signature of the CacheItemRemovedCallback delegate, to notify users when the cache item is removed and uses the CacheItemRemovedReason enumeration to tell them why it was removed. In addition, it uses the Cache..::.Item property to add objects to the cache and retrieve the value of those objects. In the AddItemToCache method, it uses the Cache..::.Add method to add an item to the cache. To use the CacheItemRemovedCallback delegate, you must add an item to the cache with this method or the Cache..::.Insert method so that that ASP.NET can automatically make the proper method calls when the item is removed. The custom RemoveItemFromCache method uses the Cache..::.Remove method to explicitly delete the item from the cache, causing the RemovedCallback method to be invoked.
<%@ Page Language="VB" %>
<html>
<Script runat=server>
Shared itemRemoved As boolean = false
Shared reason As CacheItemRemovedReason
Dim onRemove As CacheItemRemovedCallback
Public Sub RemovedCallback(k As String, v As Object, r As CacheItemRemovedReason)
itemRemoved = true
reason = r
End Sub
Public Sub AddItemToCache(sender As Object, e As EventArgs)
itemRemoved = false
onRemove = New CacheItemRemovedCallback(AddressOf Me.RemovedCallback)
If (IsNothing(Cache("Key1"))) Then
Cache.Add("Key1", "Value 1", Nothing, DateTime.Now.AddSeconds(60), Cache.NoSlidingExpiration, CacheItemPriority.High, onRemove)
End If
End Sub
Public Sub RemoveItemFromCache(sender As Object, e As EventArgs)
If (Not IsNothing(Cache("Key1"))) Then
Cache.Remove("Key1")
End If
End Sub
</Script>
<body>
<Form runat="server">
<input type=submit OnServerClick="AddItemToCache" value="Add Item To Cache" runat="server"/>
<input type=submit OnServerClick="RemoveItemFromCache" value="Remove Item From Cache" runat="server"/>
</Form>
<%
If (itemRemoved) Then
Response.Write("RemovedCallback event raised.")
Response.Write("<BR>")
Response.Write("Reason: <B>" + reason.ToString() + "</B>")
Else
Response.Write("Value of cache key: <B>" + Server.HtmlEncode(CType(Cache("Key1"),String)) + "</B>")
End If
%>
</body>
</html>
<html>
<Script runat=server language="C#">
static bool itemRemoved = false;
static CacheItemRemovedReason reason;
CacheItemRemovedCallback onRemove = null;
public void RemovedCallback(String k, Object v, CacheItemRemovedReason r){
itemRemoved = true;
reason = r;
}
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);
}
public void RemoveItemFromCache(Object sender, EventArgs e) {
if(Cache["Key1"] != null)
Cache.Remove("Key1");
}
</Script>
<body>
<Form runat="server">
<input type=submit OnServerClick="AddItemToCache" value="Add Item To Cache" runat="server"/>
<input type=submit OnServerClick="RemoveItemFromCache" value="Remove Item From Cache" runat="server"/>
</Form>
<% if (itemRemoved) {
Response.Write("RemovedCallback event raised.");
Response.Write("<BR>");
Response.Write("Reason: <B>" + reason.ToString() + "</B>");
}
else {
Response.Write("Value of cache key: <B>" + Server.HtmlEncode(Cache["Key1"] as string) + "</B>");
}
%>
</body>
</html>
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
.NET Framework
Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
Reference