Question

I have a fully dynamiclly generated page that has a set of linkbuttons basically switching views in a UpdatePanel. All that is working great except for when I have a button that is generated that needs to invoke a function to manipulate the data in the Update Panel.

.aspx

<div>
    <asp:panel runat="server" ID="buttons" />

     <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional"  >
        <ContentTemplate>
        </ContentTemplate>
     </asp:UpdatePanel>

</div>

Code Behind

Private Sub testpage_Init(sender As Object, e As System.EventArgs) Handles Me.Init
    For i As Integer = 0 To 5 'create a few dummy buttons
        Dim Btn As New LinkButton
        Btn.ID = "btn" & i.ToString
        Btn.Text = i.ToString
        AddHandler Btn.Click, AddressOf btn_Click
        buttons.Controls.Add(Btn)

        Dim Trgr As New AsyncPostBackTrigger 'async link them to the updatepanel
        Trgr.ControlID = Btn.ID
        UpdatePanel1.Triggers.Add(Trgr)
    Next
End Sub

Private Sub btn_Click(sender As Object, e As System.EventArgs)
    ScriptManager.GetCurrent(Me.Page).AddHistoryPoint(sender.id.ToString, sender.id.ToString, sender.id.ToString)

    UpdatePanel1.ContentTemplateContainer.Controls.Add(New LiteralControl(sender.id.ToString)) 'Show it got clicked

    If sender.id.ToString = "btn1" Then
        Dim Btn As New Button
        Btn.ID = "test"
        Btn.Text = "Click me"
        AddHandler Btn.Click, AddressOf subbtn_Click
        UpdatePanel1.ContentTemplateContainer.Controls.Add(Btn)
    End If
End Sub

Private Sub subbtn_Click(sender As Object, e As System.EventArgs)
    UpdatePanel1.ContentTemplateContainer.Controls.Add(New LiteralControl("It doesn't work"))
End Sub

So the problem is when the page_init is executed it does not know which linkbutton was selected so it never recreates the button and in turn never fires the event. I have seen people use the session to store the list of controls and/or the current frame but I don’t see that as an acceptable solution. Surely there has to be a way to do this.

Is there no way I can get the ScriptManager’s current/previous step information outside of the Navigate event?

Asp.net 4.0 with latest ajax toolkit.

Thanks for the help.

Answer 1

This is (I think) one of the fundamental flaws with webforms, and the ways of dealing with it are all a pain. The architecture should have included a native construct to permit event bindings to persist after a postback without recreating a control. Oftentimes you have no interest in using the control after the postback, but you are forced to track & recreate it in order to capture the event.

I usually store a list of strings containing information that can be used to recreate all the controls in ViewState; then recreate them on LoadViewState; add them to a page as the children of a placeholder control; and remove them from the placeholder again in SaveViewState. This isn’t really that awful, it’s just tedious.

Since you’re using an UpdatePanel you have the option of using the form field __EVENTTARGET which will contain the unique ID of the control that initiated an asynchronous postback. You may be able to extract what you need from that, and take whatever action you need based on that.