ObjectDataSourceDisposingEventHandler 委托

定义

表示将处理 ObjectDisposing 控件的 ObjectDataSource 事件的方法。Represents the method that will handle the ObjectDisposing event of the ObjectDataSource control.

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)

参数

sender
Object

事件的源,即 ObjectDataSourceThe source of the event, the ObjectDataSource.

示例

本部分包含两个代码示例。This section contains two code examples. 第一个代码示例演示如何将 ObjectDataSource 控件与业务对象和控件结合使用 GridView 来显示信息。The first code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to display information. 第二个代码示例提供了第一个代码示例使用的中间层业务对象示例。The second code example provides an example middle-tier business object that the first code example uses.

下面的代码示例演示如何将 ObjectDataSource 控件与业务对象和控件结合使用 GridView 来显示信息。The following code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to display information. 使用的业务对象可能会消耗非常昂贵的 (时间或资源) 为网页执行的每个数据操作创建。You might work with a business object that is very expensive (in terms of time or resources) to create for every data operation that your Web page performs. 处理昂贵对象的一种方法是创建一次实例,然后将其缓存起来进行后续操作,而不是为每个数据操作创建并销毁它。One way to work with an expensive object might be to create an instance of it once, and then cache it for subsequent operations instead of creating and destroying it for every data operation. 此示例演示了此模式。This example demonstrates this pattern. 您可以处理 ObjectCreating 事件,以便首先检查某个对象的缓存,然后创建实例(仅当尚未缓存的情况下)。You can handle the ObjectCreating event to check the cache first for an object, and then create an instance, only if one is not already cached. 然后,处理 ObjectDisposing 事件以便缓存业务对象以供将来使用,而不是将其销毁。Then, handle the ObjectDisposing event to cache the business object for future use, instead of destroying it. 在此示例中, CancelEventArgs.Cancel 类的属性 ObjectDataSourceDisposingEventArgs 设置为 true ,以指示在 ObjectDataSource Dispose 实例上不调用。In this example, the CancelEventArgs.Cancel property of the ObjectDataSourceDisposingEventArgs class is set to true, to direct the ObjectDataSource to not call Dispose on the instance.

<%@ 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中间层业务对象示例。The following code example provides an example middle-tier business object that the preceding code example uses. 此代码示例包含一个由类定义的基本业务对象,该类 EmployeeLogic 用于维护状态并封装业务逻辑。The code example consists of a basic business object, defined by the EmployeeLogic class, which is a class that maintains state and encapsulates business logic. 对于完整的工作示例,你必须将此代码编译为库,然后从 ASP 页中使用这些类。For a complete working example, you must compile this code as a library, and then use these classes from an ASP page.

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

注解

创建 ObjectDataSourceDisposingEventHandler 委托时,需要标识将要处理该事件的方法。When you create an ObjectDataSourceDisposingEventHandler delegate, you identify the method that will handle the event. 若要将事件与事件处理程序关联,请将该委托的一个实例添加到事件中。To associate the event with your event handler, add an instance of the delegate to the event. 除非移除了该委托,否则每当发生该事件时就会调用事件处理程序。The event handler is called whenever the event occurs, unless you remove the delegate. 有关如何处理事件的详细信息,请参阅 处理和引发事件For more information about how to handle events, see Handling and Raising Events.

扩展方法

GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。Gets an object that represents the method represented by the specified delegate.

适用于

另请参阅