Adding PostBackTriggers and AsyncPostBackTriggers to UpdatePanel for dynamically-generated grandchild controls - asp.net

Question

I have a page with a ScriptManager, a generic HTML drop-down list (<select>), and an UpdatePanel. The UpdatePanel contains a PlaceHolder (for now). During Page_Load, a number of user controls are added to the PlaceHolder (really, it's several instances of the same user control). The number to add is not known until the page loads, so they do need to be loaded dynamically. The drop-down list is populated with the same number of menu items, and there is javascript on the page also (using jQuery) to show only one of the controls at a time depending on the state of the drop-down list.
Each user control has two buttons that should generate an asynchronous postback, a drop-down list that should generate an asynchronous postback on a change in selected value, and a button that should generate a synchronous postback. If I was not generating the controls dynamically, and if there was only one control, the structure would be something like:
<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"
onclick="asyncButton1_Click" />
<asp:DropDownList ID="asyncDropDown" ruant="server" AutoPostBack="true"
OnSelectedIndexChanged="asyncDropDown_SelectedIndexChanged" />
<asp:Button ID="asyncButton2" runat="server" Text="Button2"
OnClick="asyncButton2_Click" />
<asp:Button ID="syncButton" runat="server" Text="SyncButton"
OnClick="syncButton_Click" />
</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>
Of course, all the controls inside the ContentTemplate would actually be part of each user control.
Adding the triggers on the server side does not seem to work because no ControlID seems to help the UpdatePanel find the relevant controls. I can use either the control's ID or the control's UniqueID, and it does not work, and I get an error along the lines of
A control with ID 'ctl00$ContentPlaceHolder1$ctl01$asyncButton1' could not be
found for the trigger in UpdatePanel 'myUpdatePanel'.
So, I wonder if I need to register the triggers in the client instead using ASP.NET Ajax. I found this page that basically explains how. However, I do not know how to get the EventName taken into consideration. The examples I have seen so far have merely been adding button clicks, but I don't know how to handle the SelectedIndexChanged event from the DropDownList.
Any help here? Are there examples out there I have missed? It doesn't help, of course, that the method in the link I gave appears to be "unofficial," so I don't see any MSDN documents on the subject.
Thanks!

Answer 1

My suggestion would be to pull all your controls inclusive this UpdatePanel out of this UpdatePanel into an UserControl. Define events in your usercontrol that are raised when the buttons are clicked or the Dropdown's selected index get changed. Handle these events in your page that holds the Placeholder(in a single UpdatePanel,conditional,without triggers). Call the Update-method of the main update panel manually if you add UserControls.
To clarify what i mean have a look at following example:
Main-page aspx:
<asp:UpdatePanel ID="Upd1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
</ContentTemplate>
</asp:UpdatePanel>
Codebehind:
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 which holds your controls:
<%# 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>
Codebehind of UserControl:
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
On this way you won't have problems with ClientID's.
Addition:
If you need access to the controls of your UserControls in the event-handlers, use one of following two options:
cast the sender's NamingContainer to the userControl's type: Dim uc As DynamicControls = DirectCast(DirectCast(sender, Control).NamingContainer, DynamicControls)
replace all occurences of (ByVal sender As Object, ByVal e As System.EventArgs) with (uc as DynamicControls). On this way the reference of your UserControl is added to the event as parameter and you could access public properties of it from the page, f.e.:
dim txt1 as String = uc.Text1
If you have exposed a property Text1 in the UserControl:
Public Property Text1() As String
Get
Return textBox1.Text
End Get
Set(ByVal value As String)
textBox1.Text = value
End Set
End Property
The second option is the cleanest and most readable way.
Update:
According to your comment: you should place the UpdateProgress in the UserControl inside of the UpdatePanel that gets updated. Remember to set the AssociatedUpdatePanelID correctly. For example:
<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>