ObjectDataSource.ObjectDisposing 事件

参考

定义

命名空间:: System.Web.UI.WebControls

程序集:: System.Web.dll

重要

一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。

在丢弃由 TypeName 属性标识的对象之前发生。

public:
 event System::Web::UI::WebControls::ObjectDataSourceDisposingEventHandler ^ ObjectDisposing;

public event System.Web.UI.WebControls.ObjectDataSourceDisposingEventHandler ObjectDisposing;

member this.ObjectDisposing : System.Web.UI.WebControls.ObjectDataSourceDisposingEventHandler

Public Custom Event ObjectDisposing As ObjectDataSourceDisposingEventHandler

事件类型

ObjectDataSourceDisposingEventHandler

示例

本部分包含两个代码示例。第一个 ObjectDataSource 代码示例演示如何将对象与业务对象和控件配合使用 GridView 来显示信息。第二个代码示例提供在第一个代码示例中使用的中间层业务对象。

下面的代码示例演示如何将 ObjectDataSource 控件与业务对象和控件配合使用 GridView 来显示信息。你可能使用业务对象，该对象在为网页执行的每个数据操作创建 (的时间或资源方面) 非常昂贵。使用昂贵对象的一种方法可能是创建一次它的实例，然后缓存它以供后续操作，而不是为每个数据操作创建和销毁它。此示例演示了此模式。可以处理 ObjectCreating 事件以先检查对象的缓存，并且仅创建它的实例（如果尚未缓存）。然后，处理 ObjectDisposing 事件以缓存业务对象以供将来使用，而不是销毁它。在此代码示例中 CancelEventArgs.Cancel ，对象的属性 ObjectDataSourceDisposingEventArgs 设置为， true 以指示 ObjectDataSource 不对对象调用 Dispose 方法。

<%@ 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>

下面的代码示例提供了前面的代码示例使用的示例中间层业务对象。代码示例由类定义 EmployeeLogic 的基本业务对象组成，该类是封装业务逻辑的有状态类。对于完整的工作示例，必须将此代码编译为库，并从 ASP.NET 页 (.aspx 文件) 使用这些类。

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

以下示例演示如何在 ObjectDisposing 将控件与 LINQ to SQL 类一起使用 ObjectDataSource 时处理事件。

Public Sub ExampleObjectDisposing(ByVal sender As Object, _
        ByVal e As ObjectDataSourceDisposingEventArgs)
    e.Cancel = True
End Sub

public void ExampleObjectDisposing(object sender,
        ObjectDataSourceDisposingEventArgs e)
{
    e.Cancel = true;
}

注解

始终在 ObjectDisposing 放弃业务对象的实例之前引发事件。如果业务对象实现 IDisposable 接口，则会在 Dispose 引发此事件后调用方法。

ObjectDisposing处理事件以调用对象上的其他方法、设置属性或执行特定于对象的清理，然后再销毁对象。对对象的引用由 ObjectInstance 属性访问，该属性由 ObjectDataSourceEventArgs 对象公开。

将控件与 LINQ to SQL 类一 ObjectDataSource 起使用时，必须取消在事件的处理程序 ObjectDisposing 中释放数据上下文类。此步骤是必需的，因为 LINQ to SQL 支持延迟执行，而 ObjectDataSource 控件会尝试在 Select 操作后释放数据上下文。

有关如何处理事件的详细信息，请参阅处理和引发事件。

适用于

ObjectDataSource.ObjectDisposing 事件

定义

事件类型

示例

注解

适用于

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