ObjectDisposing Event

ObjectDataSource.ObjectDisposing Event


Occurs before the object that is identified by the TypeName property is discarded.

Namespace:   System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

Public Event ObjectDisposing As ObjectDataSourceDisposingEventHandler

The ObjectDisposing event is always raised before the instance of the business object is discarded. If the business object implements the IDisposable interface, the Dispose method is called after this event is raised.

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. A reference to the object is accessed by the ObjectInstance property, which is exposed by the ObjectDataSourceEventArgs object.

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. 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.

For more information about how to handle events, see NIB: Consuming Events.

This section contains two code examples. The first code example demonstrates how to use an ObjectDataSource object with a business object and a GridView control to display information. The second code example provides the middle-tier business object that is used in the first code example.

The following code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to display information. 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. 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. This example demonstrates this pattern. 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. Then, handle the ObjectDisposing event to cache the business object for future use, instead of destroying it. 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.

The following code example provides the example middle-tier business object that the preceding code example uses. The code example consists of a basic business object, defined by the EmployeeLogic class, which is a stateful class that encapsulates business logic. For a complete working example, you must compile this code as a library and use these classes from an ASP.NET page (.aspx file).

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

Namespace Samples.AspNet.VB

  Public Class EmployeeLogic

    Public Sub New() 

    End Sub 'NewNew

    Public Sub New(ByVal creationTime As DateTime) 
        _creationTime = creationTime

    End Sub 'NewNew

    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

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

.NET Framework
Available since 2.0
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