CacheItemRemovedCallback 委托

  • 参考

定义

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

定义在从 Cache 移除缓存项时通知应用程序的回调方法。

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

从缓存中移除的键。

value
Object

与从缓存中移除的键关联的 Object 项。

reason
CacheItemRemovedReason

CacheItemRemovedReason 枚举指定的、从缓存移除项的原因。

示例

下面的代码示例演示了一个页面，它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 枚举来告知他们为什么删除它。 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。 在该方法中 AddItemToCache ，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 ASP.NET 可以在删除项时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，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

GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。

适用于

另请参阅