Occurs before the object that is identified by the TypeName property is discarded.
Assembly: System.Web (in System.Web.dll)
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 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 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.
<%@ 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>
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() MyClass.New(DateTime.Now) 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 ObjectDataSource control with a LINQ to SQL class.event when using an
Available since 2.0