我的建议是将包括此 UpdatePanel 在内的所有控件从此 UpdatePanel 中拉出到 UserControl 中。在您的用户控件中定义在单击按钮或下拉菜单的选定索引发生更改时引发的事件。在包含占位符的页面中处理这些事件（在单个 UpdatePanel 中，有条件，无触发器）。如果添加 UserControls，请手动调用主更新面板的更新方法。
为了澄清我的意思，请看以下示例：
主页aspx：
<asp:UpdatePanel ID="Upd1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
</ContentTemplate>
</asp:UpdatePanel>
代码隐藏：
Private Property UserControlCount() As Int32
Get
If ViewState("UserControlCount") Is Nothing Then
ViewState("UserControlCount") = 1
End If
Return DirectCast(ViewState("UserControlCount"), Int32)
End Get
Set(ByVal value As Int32)
ViewState("UserControlCount") = value
End Set
End Property
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
recreateUserControls()
End Sub
Private Sub recreateUserControls()
For i As Int32 = 1 To Me.UserControlCount
Dim uc As DynamicControls = DirectCast(Me.LoadControl("DynamicControls.ascx"), DynamicControls)
uc.ID = "DynamicControls_" & i
Addhandlers(uc)
Me.PlaceHolder1.Controls.Add(uc)
Next
End Sub
Private Sub Addhandlers(ByVal uc As DynamicControls)
AddHandler uc.asyncButton1Clicked, AddressOf ucAsyncButton1Clicked
AddHandler uc.asyncButton2Clicked, AddressOf ucAsyncButton2Clicked
AddHandler uc.syncButtonClicked, AddressOf ucSyncButtonClicked
AddHandler uc.asyncDropDownSelectedIndexChanged, AddressOf ucAsyncDropDownSelectedIndexChanged
End Sub
Private Sub addUserControl()
Me.UserControlCount += 1
Dim uc As DynamicControls = DirectCast(Me.LoadControl("DynamicControls.ascx"), DynamicControls)
uc.ID = "DynamicControls_" & Me.UserControlCount
Addhandlers(uc)
Me.PlaceHolder1.Controls.Add(uc)
Upd1.Update()
End Sub
Private Sub ucAsyncButton1Clicked(ByVal sender As Object, ByVal e As EventArgs)
'only to demonstrate how to add control dynamically and update the UpdatePanel'
addUserControl()
Me.Upd1.Update()
End Sub
Private Sub ucAsyncButton2Clicked(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Private Sub ucSyncButtonClicked(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Private Sub ucAsyncDropDownSelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
End Sub
ascx 包含您的控件：
<%@ Control Language="vb" AutoEventWireup="false" CodeBehind="DynamicControls.ascx.vb" Inherits="AJAXEnabledWebApplication1.DynamicControls" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
<asp:UpdatePanel ID="myUpdatePanel" runat="server" UpdateMode="Conditional"
ChildrenAsTriggers="false">
<ContentTemplate>
<asp:TextBox ID="textBox1" runat="server" />
<asp:TextBox ID="textBox2" runat="server" />
<asp:Button ID="asyncButton1" runat="server" Text="Button1" />
<asp:DropDownList ID="asyncDropDown" runat="server" AutoPostBack="true" />
<asp:Button ID="asyncButton2" runat="server" Text="Button2" />
<asp:Button ID="syncButton" runat="server" Text="SyncButton" />
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="asyncButton1" EventName="Click" />
<asp:AsyncPostBackTrigger ControlID="asyncButton2" EventName="Click" />
<asp:AsyncPostBackTrigger ControlID="asyncDropDown" EventName="SelectedIndexChanged" />
<asp:PostBackTrigger ControlID="syncButton" />
</Triggers>
</asp:UpdatePanel>
UserControl 的代码隐藏：
Public Partial Class DynamicControls
Inherits System.Web.UI.UserControl
Public Event asyncButton1Clicked(ByVal sender As Object, ByVal e As System.EventArgs)
Public Event asyncButton2Clicked(ByVal sender As Object, ByVal e As System.EventArgs)
Public Event syncButtonClicked(ByVal sender As Object, ByVal e As System.EventArgs)
Public Event asyncDropDownSelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)
Private Sub asyncButton1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles asyncButton1.Click
RaiseEvent asyncButton1Clicked(sender, e)
End Sub
Private Sub asyncButton2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles asyncButton2.Click
RaiseEvent asyncButton2Clicked(sender, e)
End Sub
Private Sub syncButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles syncButton.Click
RaiseEvent syncButtonClicked(sender, e)
End Sub
Private Sub asyncDropDown_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles asyncDropDown.SelectedIndexChanged
RaiseEvent asyncDropDownSelectedIndexChanged(sender, e)
End Sub
End Class
这样您就不会遇到 ClientID 的问题。
补充：
如果您需要访问事件处理程序中的 UserControls 控件，请使用以下两个选项之一：
- 将发送者的 NamingContainer 转换为 userControl 的类型：
Dim uc As DynamicControls = DirectCast(DirectCast(sender, Control).NamingContainer, DynamicControls)
-
将所有出现的(ByVal sender As Object, ByVal e As System.EventArgs) 替换为(uc as DynamicControls)。通过这种方式，您的 UserControl 的引用作为参数添加到事件中，您可以从页面访问它的公共属性，例如：
dim txt1 as String = uc.Text1
如果您在 UserControl 中公开了一个属性 Text1：
Public Property Text1() As String
Get
Return textBox1.Text
End Get
Set(ByVal value As String)
textBox1.Text = value
End Set
End Property
第二个选项是最干净和最易读的方式。
更新：
根据您的评论：您应该将 UpdateProgress 放在被更新的 UpdatePanel 内的 UserControl 中。记得正确设置AssociatedUpdatePanelID。例如：
<asp:UpdatePanel ID="UdpForm" runat="server" UpdateMode="conditional" ChildrenAsTriggers="false" >
<ContentTemplate>
<asp:panel ID="FormPanel" runat="server">
<asp:UpdateProgress ID="UpdateProgress1" DynamicLayout="true" runat="server" AssociatedUpdatePanelID="UdpForm" DisplayAfter="0" >
<ProgressTemplate>
<div class="progress">
<asp:Image ID="ImgProgress1" runat="server" ImageUrl="~/images/ajax-loader-arrows.gif" ToolTip="loading..." /> please wait...
</div>
</ProgressTemplate>
</asp:UpdateProgress>
<asp:FormView ID="FormView1" runat="server" DefaultMode="ReadOnly" >
<ItemTemplate></ItemTemplate>
<EditItemTemplate></EditItemTemplate>
<InsertItemTemplate></InsertItemTemplate>
<EmptyDataTemplate>
</EmptyDataTemplate>
<PagerTemplate >
</PagerTemplate>
</asp:FormView>
</asp:panel>
</contenttemplate>
</asp:UpdatePanel>
<asp:UpdatePanel ID="UpdContent" runat="server" UpdateMode="conditional" ChildrenAsTriggers="false" >
<ContentTemplate>
<asp:Panel ID="PnlMain" runat="server">
<asp:UpdateProgress ID="UpdateProgress2" DynamicLayout="true" runat="server" AssociatedUpdatePanelID="UpdContent" DisplayAfter="0" >
<ProgressTemplate>
<div class="progress">
<asp:Image ID="ImgProgress1" runat="server" ImageUrl="~/images/ajax-loader-arrows.gif" ToolTip="loading..." /> please wait...
</div>
</ProgressTemplate>
</asp:UpdateProgress>
Content
</asp:Panel>
</ContentTemplate>
<Triggers ></Triggers>
</asp:UpdatePanel>