ObjectDataSourceDisposingEventHandler 代理人

定義

命名空間:: System.Web.UI.WebControls

組件:: System.Web.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

代表將處理 ObjectDisposing 控制事件 ObjectDataSource 的方法。

public delegate void ObjectDataSourceDisposingEventHandler(System::Object ^ sender, ObjectDataSourceDisposingEventArgs ^ e);

public delegate void ObjectDataSourceDisposingEventHandler(object sender, ObjectDataSourceDisposingEventArgs e);

type ObjectDataSourceDisposingEventHandler = delegate of obj * ObjectDataSourceDisposingEventArgs -> unit

Public Delegate Sub ObjectDataSourceDisposingEventHandler(sender As Object, e As ObjectDataSourceDisposingEventArgs)

參數

sender: Object

事件的來源是 ObjectDataSource。

e: ObjectDataSourceDisposingEventArgs

一個 ObjectDataSourceDisposingEventArgs 包含事件資料的。

範例

本節包含兩個程式代碼範例。第一個程式碼範例示範如何將控制項與商業物件結合，並ObjectDataSource使用GridView控制項來顯示資訊。第二個範例提供了第一個範例所使用的中間層商業物件範例。

以下程式碼範例示範如何將 ObjectDataSource 控制項與商業物件 GridView 及控制項用於顯示資訊。你可能會處理一個非常昂貴（無論是時間或資源）的業務物件，為網頁執行的每一個資料操作都建立。處理昂貴物件的一種方法是先建立一次實例，然後快取以供後續操作使用，而不是每次資料操作都建立並銷毀。這個例子說明了這種模式。你可以先處理 ObjectCreating 檢查快取物件的事件，然後建立一個實例，前提是該物件尚未被快取。接著，處理 ObjectDisposing 事件以快取商業物件以供未來使用，而非銷毀它。在此範例中，CancelEventArgs.Cancel類別的性質ObjectDataSourceDisposingEventArgs設為 true，以指示不ObjectDataSource Dispose呼叫該實例。

<%@ Import namespace="Samples.AspNet.CS" %>
<%@ Page language="c#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">

// Instead of creating and destroying the business object each time, the 
// business object is cached in the ASP.NET Cache.
private void GetEmployeeLogic(object sender, ObjectDataSourceEventArgs e)
{
    // First check to see if an instance of this object already exists in the Cache.
    EmployeeLogic cachedLogic;
    
    cachedLogic = Cache["ExpensiveEmployeeLogicObject"] as EmployeeLogic;
    
    if (null == cachedLogic) {
            cachedLogic = new EmployeeLogic();            
    }
        
    e.ObjectInstance = cachedLogic;     
}

private void ReturnEmployeeLogic(object sender, ObjectDataSourceDisposingEventArgs e)
{    
    // Get the instance of the business object that the ObjectDataSource is working with.
    EmployeeLogic cachedLogic = e.ObjectInstance as EmployeeLogic;        
    
    // Test to determine whether the object already exists in the cache.
    EmployeeLogic temp = Cache["ExpensiveEmployeeLogicObject"] as EmployeeLogic;
    
    if (null == temp) {
        // If it does not yet exist in the Cache, add it.
        Cache.Insert("ExpensiveEmployeeLogicObject", cachedLogic);
    }
    
    // Cancel the event, so that the object will 
    // not be Disposed if it implements IDisposable.
    e.Cancel = true;
}
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>ObjectDataSource - C# Example</title>
  </head>
  <body>
    <form id="Form1" method="post" runat="server">

        <asp:gridview
          id="GridView1"
          runat="server"          
          datasourceid="ObjectDataSource1">
        </asp:gridview>

        <asp:objectdatasource 
          id="ObjectDataSource1"
          runat="server"          
          selectmethod="GetCreateTime"          
          typename="Samples.AspNet.CS.EmployeeLogic"
          onobjectcreating="GetEmployeeLogic"
          onobjectdisposing="ReturnEmployeeLogic" >
        </asp:objectdatasource>        

    </form>
  </body>
</html>

<%@ Import namespace="Samples.AspNet.VB" %>
<%@ Page language="vb" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">

' Instead of creating and destroying the business object each time, the 
' business object is cached in the ASP.NET Cache.
Sub GetEmployeeLogic(sender As Object, e As ObjectDataSourceEventArgs)

    ' First check to see if an instance of this object already exists in the Cache.
    Dim cachedLogic As EmployeeLogic 
    
    cachedLogic = CType( Cache("ExpensiveEmployeeLogicObject"), EmployeeLogic)
    
    If (cachedLogic Is Nothing) Then
            cachedLogic = New EmployeeLogic            
    End If
        
    e.ObjectInstance = cachedLogic
    
End Sub ' GetEmployeeLogic

Sub ReturnEmployeeLogic(sender As Object, e As ObjectDataSourceDisposingEventArgs)
    
    ' Get the instance of the business object that the ObjectDataSource is working with.
    Dim cachedLogic  As EmployeeLogic  
    cachedLogic = CType( e.ObjectInstance, EmployeeLogic)
    
    ' Test to determine whether the object already exists in the cache.
    Dim temp As EmployeeLogic 
    temp = CType( Cache("ExpensiveEmployeeLogicObject"), EmployeeLogic)
    
    If (temp Is Nothing) Then
        ' If it does not yet exist in the Cache, add it.
        Cache.Insert("ExpensiveEmployeeLogicObject", cachedLogic)
    End If
    
    ' Cancel the event, so that the object will 
    ' not be Disposed if it implements IDisposable.
    e.Cancel = True
End Sub ' ReturnEmployeeLogic
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>ObjectDataSource - VB Example</title>
  </head>
  <body>
    <form id="Form1" method="post" runat="server">

        <asp:gridview
          id="GridView1"
          runat="server"          
          datasourceid="ObjectDataSource1">
        </asp:gridview>

        <asp:objectdatasource 
          id="ObjectDataSource1"
          runat="server"          
          selectmethod="GetCreateTime"          
          typename="Samples.AspNet.VB.EmployeeLogic"
          onobjectcreating="GetEmployeeLogic"
          onobjectdisposing="ReturnEmployeeLogic" >
        </asp:objectdatasource>        

    </form>
  </body>
</html>

以下程式碼範例提供了一個中間層商業物件範例，該物件即為前述範例所使用的。程式碼範例包含一個基本的商業物件，由 EmployeeLogic 類別定義，該類別負責維護狀態並封裝商業邏輯。要完整工作範例，你必須將這些程式碼編譯成函式庫，然後從 ASP 頁面使用這些類別。

namespace Samples.AspNet.CS {

using System;
using System.Collections;
using System.Web.UI;
using System.Web.UI.WebControls;
  //
  // EmployeeLogic is a stateless business object that encapsulates
  // the operations you can perform on a NorthwindEmployee object.
  //
  public class EmployeeLogic {

    public EmployeeLogic () : this(DateTime.Now) {        
    }
    
    public EmployeeLogic (DateTime creationTime) { 
        _creationTime = creationTime;
    }

    private DateTime _creationTime;
    
    // Returns a collection of NorthwindEmployee objects.
    public ICollection GetCreateTime () {
      ArrayList al = new ArrayList();
      
      // Returns creation time for this example.      
      al.Add("The business object that you are using was created at " + _creationTime);
      
      return al;
    }
  }
}

Imports System.Collections
Imports System.Web.UI
Imports System.Web.UI.WebControls

Namespace Samples.AspNet.VB

  Public Class EmployeeLogic
    
    
    Public Sub New() 
        MyClass.New(DateTime.Now)
    
    End Sub
    
    
    Public Sub New(ByVal creationTime As DateTime) 
        _creationTime = creationTime
    
    End Sub
    
    Private _creationTime As DateTime
    
    
    ' Returns a collection of NorthwindEmployee objects.
    Public Function GetCreateTime() As ICollection 
        Dim al As New ArrayList()
        
        ' Returns creation time for this example.      
        al.Add("The business object that you are using was created at " + _creationTime)
        
        Return al
    
    End Function 'GetCreateTime
  End Class
End Namespace ' Samples.AspNet.VB

備註

當你建立 ObjectDataSourceDisposingEventHandler 代理人時，你就能確定處理事件的方法。要將事件與你的事件處理器關聯，請將該代理的實例加入事件中。事件處理程序會在事件發生時被呼叫，除非你移除代理。欲了解更多如何處理事件的資訊，請參閱「處理與提升事件」。

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

意見反應

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