ObjectDataSource.ObjectCreating ObjectDataSource.ObjectCreating ObjectDataSource.ObjectCreating ObjectDataSource.ObjectCreating Event

定义

在创建由 TypeName 属性标识的对象之前发生。Occurs before the object that is identified by the TypeName property is created.

public:
 event System::Web::UI::WebControls::ObjectDataSourceObjectEventHandler ^ ObjectCreating;
public event System.Web.UI.WebControls.ObjectDataSourceObjectEventHandler ObjectCreating;
member this.ObjectCreating : System.Web.UI.WebControls.ObjectDataSourceObjectEventHandler 
Public Custom Event ObjectCreating As ObjectDataSourceObjectEventHandler 

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对象与业务对象GridView和控件结合使用来显示信息。The first code example demonstrates how to use an ObjectDataSource object with a business object and a GridView control to display information. 第二个代码示例提供了在第一个代码示例中使用的中间层业务对象。The second code example provides the middle-tier business object that is used in the first code example.

下面的代码示例演示如何将ObjectDataSource控件与业务对象GridView和控件结合使用来显示信息。The following code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to display information. 对于您的网页执行的每个数据操作, 都可以使用非常昂贵的业务对象 (就时间或资源而言)。You might work with a business object that is very expensive to create (in terms of time or resources) for every data operation 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.

备注

在生产应用程序中, 多个请求可能会同时使用同一个实例。In a production application, multiple requests might end up simultaneously using the same instance. 因此, 需要在线程安全的方式下实现该对象。Therefore, the object needs to be implemented in a thread-safe manner.

此代码示例演示了此模式。This code example demonstrates this pattern. 您可以处理ObjectCreating事件以首先检查某个对象的缓存, 并且仅创建该对象的实例 (如果尚未缓存)。You can handle the ObjectCreating event to check the cache for an object first, and only create an instance of the object, 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. 在此代码示例中, CancelEventArgs.CancelObjectDataSourceDisposingEventArgs对象的属性ObjectDataSource设置为true , 以指示对对象不调用Dispose方法。In this code example, the CancelEventArgs.Cancel property of the ObjectDataSourceDisposingEventArgs object is set to true to direct the ObjectDataSource to not call Dispose method on the object.

<%@ 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 the example middle-tier business object that the preceding code example uses. 此代码示例包含一个由EmployeeLogic类定义的基本业务对象, 该类是封装业务逻辑的有状态类。The code example consists of a basic business object, defined by the EmployeeLogic class, which is a stateful class that encapsulates business logic. 若要获取完整的工作示例, 必须将此代码编译为库, 并从 ASP.NET 页 (.aspx 文件) 使用这些类。For a complete working example, you must compile this code as a library and use these classes from an ASP.NET page (.aspx file).

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

如果标识为执行数据操作的方法static是 (Shared在 Visual Basic 中), 则ObjectCreating永远不会ObjectCreated引发和事件。If the method that is identified to perform the data operation is static (Shared in Visual Basic), the ObjectCreating and ObjectCreated events are never raised.

ObjectDataSource控件自动调用业务对象的无参数构造函数, 以使用反射来创建它的实例。The ObjectDataSource control automatically calls the parameterless constructor of a business object to create an instance of it using reflection. 处理事件以显式调用另一个构造函数, 并将生成的对象实例设置ObjectInstance为关联ObjectDataSourceEventArgs对象的属性。 ObjectCreatingHandle the ObjectCreating event to explicitly call another constructor, and set the instance of the object that results to the ObjectInstance property of the associated ObjectDataSourceEventArgs object.

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.

适用于

另请参阅