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AsyncPostBackTrigger Class

Defines a control and optional event of the control as an asynchronous postback control trigger that causes an UpdatePanel control to refresh.

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

[AspNetHostingPermissionAttribute(SecurityAction.LinkDemand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermissionAttribute(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
public class AsyncPostBackTrigger : UpdatePanelControlTrigger

Use the AsyncPostBackTrigger control to enable controls to be triggers for an UpdatePanel control. Controls that are triggers for an update panel cause a refresh of the panel's content after an asynchronous postback. Defining an asynchronous trigger control is useful in the following scenarios:

  • For controls that are outside a panel.

  • For controls that are inside a panel when the ChildrenAsTriggers property is false.

  • For controls that are inside nested panels, in order to cause a refresh of parent panels.

The control that the AsyncPostBackTrigger control references must be in the same naming container as the update panel for which it is a trigger. Triggers that are based on controls in other naming containers are not supported.

Add AsyncPostBackTrigger controls either by using the UpdatePanelTrigger Collection Editor dialog box in the designer or by creating a Triggers element declaratively in the UpdatePanel control. The ControlID property is required, but the EventName property is optional. If the EventName property is not specified, the DefaultEventAttribute attribute of the control is used to determine the default event. For example, the default event for the Button control is the Click event. The EventName property is case-insensitive.

You can also reference a naming container as a trigger. In that case, all child controls in the container that cause a postback are considered triggers for the UpdatePanel control.

Programmatically adding AsyncPostBackTrigger controls is not supported. To programmatically register a postback control, use the RegisterAsyncPostBackControl method of the ScriptManager control. Then call the Update method of the UpdatePanel control when the control posts back.

If you define a control using both PostBackTrigger and AsyncPostBackTrigger, an exception is thrown.

The following example shows how to add an AsyncPostBackTrigger control declaratively. A Button control that is outside an UpdatePanel control lets users enter a search term to find in the Products table of the Northwind database. A GridView control that is inside the UpdatePanel control shows the results. The Button control is specified as an asynchronous trigger for the UpdatePanel control.

<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"  

<script runat="server">
    protected void Button1_Click(object sender, EventArgs e)
        SqlDataSource1.SelectParameters["SearchTerm"].DefaultValue = 
        Label1.Text = "Searching for '" + 
            Server.HtmlEncode(TextBox1.Text) + "'";


<html xmlns="">
<head runat="server">
    <title>AsyncPostBackTrigger Example</title>
    <form id="form1" defaultbutton="Button1"
          defaultfocus="TextBox1" runat="server">
            <asp:ScriptManager ID="ScriptManager1" runat="server" />
            <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            <asp:Button ID="Button1" Text="Submit" 
                        OnClick="Button1_Click" runat="server"  />
            <asp:UpdatePanel ID="UpdatePanel1" UpdateMode="Conditional" 
                  <asp:AsyncPostBackTrigger ControlID="Button1" />
                    <hr />
                    <asp:Label ID="Label1" runat="server"/>
                    <br />
                    <asp:GridView ID="GridView1" runat="server" AllowPaging="True"
                        Enter a search term.
                    <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
                        ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
                        SelectCommand="SELECT [ProductName], [UnitsInStock] FROM 
                        [Alphabetical list of products] WHERE ([ProductName] LIKE 
                        '%' + @SearchTerm + '%')">
                            <asp:Parameter Name="SearchTerm" Type="String" />

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

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

.NET Framework

Supported in: 3.5