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Page.RegisterAsyncTask Method

Registers a new asynchronous task with the page.

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

'Declaration
Public Sub RegisterAsyncTask ( _
	task As PageAsyncTask _
)

Parameters

task
Type: System.Web.UI.PageAsyncTask

A PageAsyncTask that defines the asynchronous task.

ExceptionCondition
ArgumentNullException

The asynchronous task is Nothing.

Define an asynchronous task using the PageAsyncTask class. When the task is defined, use the RegisterAsyncTask method to register the task with the page. After registering the task, invoke the ExecuteRegisteredAsyncTasks method to begin the asynchronous task.

The RegisterAsyncTask method can be used with both synchronous and asynchronous pages.

The following code example demonstrates the use of the AsyncTimeout property with the ExecuteRegisteredAsyncTasks and RegisterAsyncTask methods. Note the use of beginning, ending, and time-out handlers. In the example, an artificial delay is introduced to demonstrate the situation of an asynchronous task exceeding the allotted time for the task as specified in the AsyncTimeout property. In a real-world scenario, an asynchronous task could be used to perform database calls or image generation, for example, and the time-out handler provides graceful degradation if the task is not performed in a specified amount of time.

<%@ Page Language="VB" AsyncTimeout="2"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">

  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)

    ' Define the asynchronuous task.
    Dim mytask As New Samples.AspNet.VB.Controls.MyAsyncTask()
    Dim asynctask As New PageAsyncTask(AddressOf mytask.OnBegin, AddressOf mytask.OnEnd, AddressOf mytask.OnTimeout, DBNull.Value)

    ' Register the asynchronous task.
    Page.RegisterAsyncTask(asynctask)

    ' Execute the register asynchronous task.
    Page.ExecuteRegisteredAsyncTasks()

    TaskMessage.InnerHtml = mytask.GetAsyncTaskProgress()

  End Sub
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Asynchronous Task Example</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
      <span id="TaskMessage" runat="server">
      </span>
    </div>
    </form>
</body>
</html>
Imports Microsoft.VisualBasic
Imports System
Imports System.Web
Imports System.Web.UI
Imports System.Threading

Namespace Samples.AspNet.VB.Controls

    Public Class MyAsyncTask

        Private _taskprogress As String 
        Private _dlgt As AsyncTaskDelegate

        ' Create delegate. 
        Delegate Function AsyncTaskDelegate()

        Public Function GetAsyncTaskProgress() As String 
            Return _taskprogress
        End Function 

        Public Function DoTheAsyncTask()

            ' Introduce an artificial delay to simulate a delayed  
            ' asynchronous task. Make this greater than the  
            ' AsyncTimeout property.
            Thread.Sleep(TimeSpan.FromSeconds(5.0))

        End Function 


        ' Define the method that will get called to 
        ' start the asynchronous task. 
        Public Function OnBegin(ByVal sender As Object, ByVal e As EventArgs, ByVal cb As AsyncCallback, ByVal extraData As Object) As IAsyncResult

            _taskprogress = "Beginning async task." 

            Dim _dlgt As New AsyncTaskDelegate(AddressOf DoTheAsyncTask)
            Dim result As IAsyncResult = _dlgt.BeginInvoke(cb, extraData)
            Return result

        End Function 'OnBegin

        ' Define the method that will get called when 
        ' the asynchronous task is ended. 
        Public Sub OnEnd(ByVal ar As IAsyncResult)

            _taskprogress = "Asynchronous task completed."
            _dlgt.EndInvoke(ar)

        End Sub 

        ' Define the method that will get called if the task 
        ' is not completed within the asynchronous timeout interval. 
        Public Sub OnTimeout(ByVal ar As IAsyncResult)

            _taskprogress = "Ansynchronous task failed to complete because " & _
            "it exceeded the AsyncTimeout parameter." 

        End Sub 

    End Class 

End Namespace

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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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