CacheItemRemovedCallback 委托

定义

命名空间:
System.Web.Caching
程序集:
System.Web.dll

定义一个回调方法，用于在从中删除 Cache缓存项时通知应用程序。

public delegate void CacheItemRemovedCallback(System::String ^ key, System::Object ^ value, CacheItemRemovedReason reason);
public delegate void CacheItemRemovedCallback(string key, object value, CacheItemRemovedReason reason);
type CacheItemRemovedCallback = delegate of string * obj * CacheItemRemovedReason -> unit
Public Delegate Sub CacheItemRemovedCallback(key As String, value As Object, reason As CacheItemRemovedReason)

参数

key
String

从缓存中删除的密钥。

value
Object

Object与从缓存中删除的键关联的项。

reason
CacheItemRemovedReason

从缓存中删除项的原因，由 CacheItemRemovedReason 枚举指定。

示例

下面的代码示例演示了一个页面，该页面向用户显示分配给缓存中某个项的值，然后在从缓存中删除该项时通知他们。 它创建一个 RemovedCallback 方法，该方法使用委托的 CacheItemRemovedCallback 签名，在删除缓存项时通知用户，并使用 CacheItemRemovedReason 枚举告诉他们为什么删除它。 此外，它还使用 Cache.Item[] 属性将对象添加到缓存并检索这些对象的值。 在 AddItemToCache 方法中，它使用 Cache.Add 该方法将项添加到缓存中。 若要使用 CacheItemRemovedCallback 委托，必须使用此方法或 Cache.Insert 方法将项添加到缓存中，以便删除项时，ASP.NET 可以自动进行正确的方法调用。 自定义 RemoveItemFromCache 方法使用 Cache.Remove 该方法从缓存中显式删除项，从而导致 RemovedCallback 调用该方法。

<html>
 <Script runat=server language="C#">
// <snippet2>
    static bool itemRemoved = false;
    static CacheItemRemovedReason reason;
    CacheItemRemovedCallback onRemove = null;

    public void RemovedCallback(String k, Object v, CacheItemRemovedReason r){
      itemRemoved = true;
      reason = r;
    }
// </snippet2>

// <snippet3>
    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);
    }
// </snippet3>

// <snippet4>
    public void RemoveItemFromCache(Object sender, EventArgs e) {
        if(Cache["Key1"] != null)
          Cache.Remove("Key1");
    }
// </snippet4>
 </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 {
// <snippet5>
        Response.Write("Value of cache key: <B>" + Server.HtmlEncode(Cache["Key1"] as string) + "</B>");
// </snippet5>
     }
  %>
 </body>
</html>

<%@ Page Language="VB" %>

<html>
 <Script runat=server>
' <snippet2>
    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
' </snippet2>

' <snippet3>
    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
' </snippet3>

' <snippet4>
    Public Sub RemoveItemFromCache(sender As Object, e As EventArgs)
        If (Not IsNothing(Cache("Key1"))) Then
          Cache.Remove("Key1")
        End If
    End Sub
' </snippet4>
 </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
' <snippet5>
    Response.Write("Value of cache key: <B>" + Server.HtmlEncode(CType(Cache("Key1"),String)) + "</B>")
' </snippet5>
End If
%>
 </body>
</html>

扩展方法

名称 说明
GetMethodInfo(Delegate)

获取一个对象，该对象表示由指定委托表示的方法。

适用于

另请参阅