Assembly: System.Web (in System.Web.dll)
Thetype exposes the following members.
|Equals(Object)||Determines whether the specified object is equal to the current object. (Inherited from Object.)|
|Finalize||Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)|
|GetHashCode||Serves as the default hash function. (Inherited from Object.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|ToString||Returns a string that represents the current object. (Inherited from Object.)|
The class is used in the OnObjectDisposing method to provide access to the business object instance after any data operations that are using the ObjectDataSource control and business object are performed, but before the business object is destroyed. The business object is accessed using the ObjectInstance property. By adding a delegate to handle the ObjectDisposing event, you can access any publicly exposed members of the business object to perform any final work or clean up.
The OnObjectDisposing method is not called by the ObjectDataSource control, if the method that performs data operations is a static method. No business object instance is created when the method is static.
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 display information. The second code example provides the example middle-tier 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 display information. You might work with a business object that is very expensive (in terms of time or resources) to create for every data operation that 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 then create an instance, only 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 example, the CancelEventArgs.Cancel property of the object is set to true, to direct the ObjectDataSource to not call the Dispose method on the instance.
<%@ 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 an 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 class that maintains state and encapsulates business logic. For a complete working example, you must compile this code as a library, and then use these classes from an ASP page.
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 '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