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IPostBackDataHandler Interface

Defines methods that ASP.NET server controls must implement to automatically load postback data.

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

'Declaration
Public Interface IPostBackDataHandler

The IPostBackDataHandler type exposes the following members.

  NameDescription
Public methodLoadPostDataWhen implemented by a class, processes postback data for an ASP.NET server control.
Public methodRaisePostDataChangedEventWhen implemented by a class, signals the server control to notify the ASP.NET application that the state of the control has changed.
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You must implement the IPostBackDataHandler interface when creating a server control that needs to examine form data that is posted back to the server by the client. The contract that this interface defines allows a server control to determine whether its state should be altered as a result of the postback, and to raise the appropriate events. For more information, see Server Event Handling in ASP.NET Web Pages.

The following code example demonstrates a custom text box server control that implements the IPostBackDataHandler interface. The Text property is changed as a result of the postback, and the server control raises a TextChanged event after postback data has been loaded.


Imports System
Imports System.Web
Imports System.Web.UI
Imports System.Collections
Imports System.Collections.Specialized

Namespace CustomWebFormsControls

    <System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> Public Class MyTextBox
        Inherits Control
        Implements IPostBackDataHandler


        Public Property Text() As String
            Get
                Return CType(Me.ViewState("Text"), String)
            End Get

            Set
                Me.ViewState("Text") = value
            End Set
        End Property


        Public Event TextChanged As EventHandler


        Public Overridable Shadows Function LoadPostData( _
        postDataKey As String, _
        postCollection As System.Collections.Specialized.NameValueCollection) _
        As Boolean Implements IPostBackDataHandler.LoadPostData

            Dim presentValue As String = Text
            Dim postedValue As String = postCollection(postDataKey)

            If presentValue Is Nothing Or Not presentValue.Equals(postedValue) Then
                Text = postedValue
                Return True
            End If

            Return False
        End Function


        Public Overridable Shadows Sub RaisePostDataChangedEvent() _
        Implements IPostBackDataHandler.RaisePostDataChangedEvent

            OnTextChanged(EventArgs.Empty)
        End Sub


        Protected Overridable Sub OnTextChanged(e As EventArgs)
            RaiseEvent TextChanged(Me, e)
        End Sub


        Protected Overrides Sub Render(output As HtmlTextWriter)
            output.Write("<INPUT type= text name = " & Me.UniqueID & _
                " value = " & Me.Text & " >")
        End Sub

    End Class

End Namespace



.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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