CacheItemRemovedCallback 代理人

定義

命名空間:
System.Web.Caching
組件:
System.Web.dll

定義了一種回調方法，用於通知應用程式快取項目被移除 Cache。

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)

參數

key
String

就是從快取中移除的金鑰。

value
Object

Object與金鑰相關的項目從快取中移除。

reason
CacheItemRemovedReason

項目被從快取中移除的原因，依列 CacheItemRemovedReason 舉方式所規定。

範例

以下程式碼範例展示了一個頁面，向使用者展示快取中某項目的值，並在該項目從快取中移除時通知使用者。 它建立一種 RemovedCallback 方法，利用代理的簽名 CacheItemRemovedCallback 通知使用者快取項目被移除，並利用 CacheItemRemovedReason 列舉說明為何被移除。 此外，它還會利用 屬性 Cache.Item[] 將物件加入快取並取得這些物件的值。 在該 AddItemToCache 方法中，它使用 的方法 Cache.Add 將項目加入快取。 要使用 CacheItemRemovedCallback 代理，必須用此方法或 Cache.Insert 方法將項目加入快取，這樣當項目被移除時，ASP.NET 才能自動進行正確的方法呼叫。 自訂 RemoveItemFromCache 方法會利用該 Cache.Remove 方法明確刪除快取中的項目，導致 RemovedCallback 該方法被呼叫。

<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>

擴充方法

名稱 Description
GetMethodInfo(Delegate)

取得一個代表指定代理所代表方法的物件。

適用於

另請參閱