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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)

public class AsyncPostBackTrigger : UpdatePanelControlTrigger

The AsyncPostBackTrigger type exposes the following members.

Public methodAsyncPostBackTriggerInitializes a new instance of an AsyncPostBackTrigger class.

Public propertyControlIDGets or sets the name of the control that triggers an asynchronous postback for an UpdatePanel control.
Public propertyEventNameGets or sets the postback control event that triggers an UpdatePanel control to be updated.
Public propertyOwnerGets a reference to the UpdatePanel control that the UpdatePanelTrigger targets. (Inherited from UpdatePanelTrigger.)

Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Protected methodFindTargetControlSearches for the control specified in the ControlID property. (Inherited from UpdatePanelControlTrigger.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodHasTriggeredReturns a value that indicates whether the trigger was invoked. (Overrides UpdatePanelTrigger.HasTriggered().)
Protected methodInitializeInitializes the AsyncPostBackTrigger control and determines whether the event that is named in the trigger exists and is valid. (Overrides UpdatePanelTrigger.Initialize().)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodOnEventInfrastructure. Raises the event that will trigger a postback and refresh of an UpdatePanel control.
Public methodToStringReturns a string representation of the current AsyncPostBackTrigger control. (Overrides Object.ToString().)

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" />

.NET Framework

Supported in: 4, 3.5

Windows 7, Windows Vista SP1 or later, Windows XP SP3, 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.

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