ObjectDataSourceFilteringEventHandler Delegate


Represents the method that will handle the Filtering event of the ObjectDataSource control.

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

Public Delegate Sub ObjectDataSourceFilteringEventHandler (
	sender As Object,
	e As ObjectDataSourceFilteringEventArgs


Type: System.Object

The source of the event, the ObjectDataSource.

Type: System.Web.UI.WebControls.ObjectDataSourceFilteringEventArgs

An ObjectDataSourceFilteringEventArgs that contains the event data.

When you create an ObjectDataSourceFilteringEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event handler delegates, see NIB: Consuming Events.

This section contains two code examples. The first code example demonstrates how to display filtered data by using an ObjectDataSource control to retrieve data from a middle-tier business object, and then using a GridView control to display the results. The second code example provides an example of a middle-tier business object that is used by the first code example.

The following code example demonstrates how to display filtered data by using an ObjectDataSource control to retrieve data from a middle-tier business object, and then using a GridView control to display the results. The ObjectDataSource control can filter data only when the method that retrieves the data retrieves it as a DataSet or DataTable object. For this reason, the SelectMethod property identifies a business object method that retrieves data as a DataSet or DataTable object.

The code example consists of a TextBox control, a GridView control, the ObjectDataSource control, and a Submit button. By default, the TextBox control is populated with the name of one of the employees at Northwind Traders. The GridView control displays information about the employee who is identified by the name in the TextBox. To retrieve data for another employee, in the TextBox control, type the full name of the employee, and then click the Submit button.

The FilterExpression property specifies an expression that is used to filter the data that is retrieved by the method that is specified by the SelectMethod property. It uses parameter placeholders that are evaluated to the parameters that are contained in the FilterParameters collection. In this example, the parameter placeholder is enclosed by single quotation marks (') because the type of the parameter is a string type that might contain spaces. If the type of the parameter is numeric or date, quotation marks are not required. The FilterParameters collection contains one parameter, a FormParameter object that is bound to the TextBox control.

If no name is specified in the TextBox control, a new parameter is added to the ParameterValues collection so that the search is successful.

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.VB" Assembly="Samples.AspNet.VB" %>
<%@ Page language="vb" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<script runat="server">

    Protected Sub ObjectDataSource1_Filtering(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.ObjectDataSourceFilteringEventArgs)
        If Textbox1.Text = "" Then
            e.ParameterValues.Add("FullName", "Nancy Davolio")
        End If
    End Sub

<html xmlns="http://www.w3.org/1999/xhtml" >
    <title>ObjectDataSource - VB Example</title>
    <form id="Form1" method="post" runat="server">

        <p>Show all users with the following name.</p>

        <asp:textbox id="Textbox1" runat="server" text="Nancy Davolio" />

            <asp:boundfield headertext="ID" datafield="EmpID" />
            <asp:boundfield headertext="Name" datafield="FullName" />
            <asp:boundfield headertext="Street Address" datafield="Address" />

        <!-- Security Note: The ObjectDataSource uses a FormParameter,
             Security Note: which does not perform validation of input from the client. -->

          filterexpression="FullName='{0}'" OnFiltering="ObjectDataSource1_Filtering">
              <asp:formparameter name="FullName" formfield="Textbox1" defaultvalue="Nancy Davolio" />

        <p><asp:button id="Button1" runat="server" text="Search" /></p>


The following code example provides an example of a middle-tier business object that the preceding code example uses. The code example consists of two basic classes: EmployeeLogic and NorthwindEmployee. The EmployeeLogic class encapsulates business logic and the NorthwindEmployee class is a model class that contains only the basic functionality that is required to load and persist data from the data tier. For simplicity, the EmployeeLogic class creates a static set of data, rather than retrieving the data from a data tier. For a complete working example, you must compile and use these classes with the Web Forms code examples that are provided.

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

Namespace Samples.AspNet.VB
' EmployeeLogic is a stateless business object that encapsulates 
' the operations you can perform on a NorthwindEmployee object.
Public Class EmployeeLogic

   ' Returns a collection of NorthwindEmployee objects.
   Public Shared Function GetAllEmployees() As ICollection
      Dim data As New ArrayList()

      data.Add(New NorthwindEmployee(1, "Nancy", "Davolio", "507 - 20th Ave. E. Apt. 2A"))
      data.Add(New NorthwindEmployee(2, "Andrew", "Fuller", "908 W. Capital Way"))
      data.Add(New NorthwindEmployee(3, "Janet", "Leverling", "722 Moss Bay Blvd."))
      data.Add(New NorthwindEmployee(4, "Margaret", "Peacock", "4110 Old Redmond Rd."))
      data.Add(New NorthwindEmployee(5, "Steven", "Buchanan", "14 Garrett Hill"))
      data.Add(New NorthwindEmployee(6, "Michael", "Suyama", "Coventry House Miner Rd."))
      data.Add(New NorthwindEmployee(7, "Robert", "King", "Edgeham Hollow Winchester Way"))

      Return data
   End Function 'GetAllEmployees

   Public Shared Function GetEmployee(anID As Object) As NorthwindEmployee
      Dim data As ArrayList = CType(GetAllEmployees(), ArrayList)
      Dim empID As Integer = Int32.Parse(anID.ToString())
      Return CType(data(empID),NorthwindEmployee)   
   End Function 'GetEmployee

   ' To support basic filtering, the employees cannot
   ' be returned as an array of objects, rather as a 
   ' DataSet of the raw data values. 
   Public Shared Function GetAllEmployeesAsDataSet() As DataSet
      Dim employees As ICollection = GetAllEmployees()

      Dim ds As New DataSet("Table")

      ' Create the schema of the DataTable.
      Dim dt As New DataTable()
      Dim dc As DataColumn
      dc = New DataColumn("EmpID", GetType(Integer))
      dc = New DataColumn("FullName", GetType(String))
      dc = New DataColumn("Address", GetType(String))

      ' Add rows to the DataTable.
      Dim row As DataRow
      Dim ne As NorthwindEmployee
      For Each ne In employees         
         row = dt.NewRow()
         row("EmpID") = ne.EmpID
         row("FullName") = ne.FullName
         row("Address") = ne.Address
      ' Add the complete DataTable to the DataSet.

      Return ds
   End Function 'GetAllEmployeesAsDataSet

End Class 'EmployeeLogic 

Public Class NorthwindEmployee

   Public Sub New(anID As Integer, aFirstName As String, aLastName As String, anAddress As String)
      ID = anID
      Me.aFirstName = aFirstName
      Me.aLastName = aLastName
      Me.aAddress = anAddress
   End Sub 'NewNew

   Private ID As Object   
   Public ReadOnly Property EmpID() As String
         Return ID.ToString()
      End Get
   End Property 

   Private aLastName As String   
   Public Property LastName() As String
         Return aLastName
      End Get
         aLastName = value
      End Set
   End Property 

   Private aFirstName As String   
   Public Property FirstName() As String
         Return aFirstName
      End Get
         aFirstName = value
      End Set
   End Property 

   Public ReadOnly Property FullName() As String
         Return FirstName & " " & LastName
      End Get
   End Property 

   Private aAddress As String  
   Public Property Address() As String
         Return aAddress
      End Get
         aAddress = value
      End Set
   End Property 

End Class 'NorthwindEmployee
End Namespace

.NET Framework
Available since 2.0
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