Assembly: System.Web (in System.Web.dll)
'Declaration <AspNetHostingPermissionAttribute(SecurityAction.LinkDemand, Level := AspNetHostingPermissionLevel.Minimal)> _ <AspNetHostingPermissionAttribute(SecurityAction.InheritanceDemand, Level := AspNetHostingPermissionLevel.Minimal)> _ Public Class ObjectDataSourceEventArgs _ Inherits EventArgs 'Usage Dim instance As ObjectDataSourceEventArgs
The class is used in the OnObjectCreating and OnObjectCreated methods to provide access to the business object instance before any data operations that are using the ObjectDataSource control and business object are performed. The business object is set and accessed using the ObjectInstance property. By adding an event handler delegate to handle the ObjectCreating event, you can create an instance of the business object in custom code instead of the ObjectDataSource performing the instantiation. This is useful when you want a non-default instance of your business object or to call a non-default constructor to create the instance; the ObjectDataSource always calls the default constructor to create an instance of the business object it works with. You can also add an event handler delegate to handle the ObjectCreated event, which enables you to access any publicly exposed members of the business object to perform any additional initialization or work.
The ObjectDataSource control exposes many events that you can handle to work with the underlying business object at various times in its lifecycle. The following table lists the events and the associated EventArgs classes and event handler delegates.
Occurs immediately before the instance of the business object is created.
Occurs immediately after the instance of the business object is created.
Occurs before the data is retrieved.
Occur before an insert, update, or delete operation is performed.
Occurs after the data is retrieved.
Occur after the insert, update, or delete operation is completed.
Occurs before a business object is destroyed.
This section contains two code examples. The first code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to retrieve and display information. The second code example provides the example basic business object that the first code example uses.
The following code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to retrieve and display information. In this example, as in many real-world scenarios, it might not be possible nor appropriate to use a default instance of the business object with the ObjectDataSource control. In this example, the ObjectDataSource cannot successfully call the default constructor because it will throw an exception. In some cases, the default constructor might be protected and in others it might not initialize the business object to a desired state. Whatever the reason, you can create an instance of the business object yourself and set the instance to the ObjectInstance property of the object that is passed to the handler. This is the business object instance that the ObjectDataSource will use to perform its work.
<%@ 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"> Private Sub NorthwindLogicCreating(sender As Object, e As ObjectDataSourceEventArgs) ' Create an instance of the business object using a non-default constructor. Dim eLogic As EmployeeLogic = New EmployeeLogic("Not created by the default constructor!") ' Set the ObjectInstance property so that the ObjectDataSource uses the created instance. e.ObjectInstance = eLogic End Sub ' NorthwindLogicCreating </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="GetAllEmployees" onobjectcreating="NorthwindLogicCreating" typename="Samples.AspNet.VB.EmployeeLogic" > </asp:objectdatasource> </form> </body> </html>
The following code example demonstrates the example basic business object that the preceding code example uses.
Imports System Imports System.Collections Imports System.Web.UI Imports System.Web.UI.WebControls Namespace Samples.AspNet.VB Public Class EmployeeLogic Public Sub New() Throw New NotSupportedException("Initialize data.") End Sub 'New Public Sub New(ByVal data As String) _data = data End Sub 'New Private _data As String ' Returns a collection of NorthwindEmployee objects. Public Function GetAllEmployees() As ICollection Dim al As New ArrayList() al.Add(_data) Return al End Function 'GetAllEmployees End Class 'EmployeeLogic End Namespace ' Samples.AspNet.VB
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The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.