ObjectDataSource.ObjectDisposing ObjectDataSource.ObjectDisposing ObjectDataSource.ObjectDisposing ObjectDataSource.ObjectDisposing Event

Definizione

Si verifica prima dell'eliminazione dell'oggetto identificato dalla proprietà TypeName.Occurs before the object that is identified by the TypeName property is discarded.

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 

Esempi

In questa sezione sono riportati due esempi di codice.This section contains two code examples. Nel primo esempio di codice viene illustrato come utilizzare ObjectDataSource un oggetto con un oggetto business e GridView un controllo per visualizzare le informazioni.The first code example demonstrates how to use an ObjectDataSource object with a business object and a GridView control to display information. Il secondo esempio di codice fornisce l'oggetto business di livello intermedio usato nel primo esempio di codice.The second code example provides the middle-tier business object that is used in the first code example.

Nell'esempio di codice riportato di seguito viene illustrato ObjectDataSource come utilizzare un controllo con un oggetto GridView business e un controllo per visualizzare le informazioni.The following code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to display information. È possibile utilizzare un oggetto business molto costoso da creare (in termini di tempo o risorse) per ogni operazione sui dati eseguita dalla pagina Web.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. Un modo per utilizzare un oggetto costoso potrebbe consistere nel creare un'istanza di una sola volta e quindi memorizzarla nella cache per le operazioni successive anziché crearla ed eliminarla per ogni operazione sui dati.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. Questo esempio illustra questo modello.This example demonstrates this pattern. È possibile gestire l' ObjectCreating evento per controllare innanzitutto la cache di un oggetto e crearne un'istanza, se non è già memorizzato nella cache.You can handle the ObjectCreating event to check the cache for an object first, and only create an instance of it, if one is not already cached. Quindi, gestire l' ObjectDisposing evento per memorizzare nella cache l'oggetto business per un uso futuro, anziché eliminarlo definitivamente.Then, handle the ObjectDisposing event to cache the business object for future use, instead of destroying it. In questo esempio di codice, CancelEventArgs.Cancel la proprietà ObjectDataSourceDisposingEventArgs dell'oggetto viene ObjectDataSource impostata true su per indicare a di non chiamare il Dispose metodo sull'oggetto.In this code example, the CancelEventArgs.Cancel property of the ObjectDataSourceDisposingEventArgs object is set to true to direct the ObjectDataSource to not call the 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>

Nell'esempio di codice riportato di seguito viene fornito l'oggetto business di livello intermedio di esempio utilizzato nell'esempio di codice precedente.The following code example provides the example middle-tier business object that the preceding code example uses. L'esempio di codice è costituito da un oggetto business di base EmployeeLogic , definito dalla classe, che è una classe con stato che incapsula la logica di business.The code example consists of a basic business object, defined by the EmployeeLogic class, which is a stateful class that encapsulates business logic. Per un esempio di funzionamento completo, è necessario compilare questo codice come una libreria e usare queste classi da una pagina ASP.NET (file con estensione aspx).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 'New
    
    
    Public Sub New(ByVal creationTime As DateTime) 
        _creationTime = creationTime
    
    End Sub 'New
    
    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 'EmployeeLogic
End Namespace ' Samples.AspNet.VB

Nell'esempio seguente viene illustrato come gestire l' ObjectDisposing evento quando si utilizza ObjectDataSource un controllo con una classe LINQ to SQL.The following example shows how to handle the ObjectDisposing event when using an ObjectDataSource control with a LINQ to SQL class.

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;  
}  

Commenti

L' ObjectDisposing evento viene sempre generato prima che l'istanza dell'oggetto business venga eliminata.The ObjectDisposing event is always raised before the instance of the business object is discarded. Se l'oggetto business implementa l' IDisposable interfaccia, il Dispose metodo viene chiamato dopo la generazione di questo evento.If the business object implements the IDisposable interface, the Dispose method is called after this event is raised.

Gestire l' ObjectDisposing evento per chiamare altri metodi sull'oggetto, impostare le proprietà o eseguire operazioni di pulizia specifiche per l'oggetto prima che l'oggetto venga eliminato definitivamente.Handle the ObjectDisposing event to call other methods on the object, set properties, or perform clean-up that is specific to the object before the object is destroyed. Il ObjectInstance riferimento all'oggetto è accessibile dalla proprietà, esposta ObjectDataSourceEventArgs dall'oggetto.A reference to the object is accessed by the ObjectInstance property, which is exposed by the ObjectDataSourceEventArgs object.

Quando si usa un ObjectDataSource controllo con una classe LINQ to SQL, è necessario annullare l'eliminazione della classe del contesto dati in un gestore per l' ObjectDisposing evento.When you use a ObjectDataSource control with a LINQ to SQL class, you must cancel the disposing of the data-context class in an handler for the ObjectDisposing event. Questo passaggio è necessario perché LINQ to SQL supporta l'esecuzione posticipata, mentre il ObjectDataSource controllo tenta di eliminare il contesto dati dopo l'operazione di selezione.This step is necessary because LINQ to SQL supports deferred execution, whereas the ObjectDataSource control tries to dispose the data context after the Select operation.

Per altre informazioni su come gestire gli eventi, vedere la gestione e generazione di eventi.For more information about how to handle events, see Handling and Raising Events.

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