IPostBackDataHandler Interface
Defines methods that ASP.NET server controls must implement to automatically load postback data.
Assembly: System.Web (in System.Web.dll)
| Name | Description | |
|---|---|---|
![]() | LoadPostData(String, NameValueCollection) | When implemented by a class, processes postback data for an ASP.NET server control. |
![]() | RaisePostDataChangedEvent() | When implemented by a class, signals the server control to notify the ASP.NET application that the state of the control has changed. |
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 Forms 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
Available since 1.1
