Dynamic Event Handler not Firing

Question 1

Dynamic controls can be a bit tricky because of ViewState

Basically: you were adding the dynamic controls in response to the TextChanged event, which fires after Init and Load and after the ViewState was deserialized. Therefore you were experiencing the problem because the ViewState was not aware of the dynamic controls and was out of sync with your expectations. By checking the value of txtEnter.Text in the Load phase and creating the controls there, you can make your ViewState aware of the controls (which, remember, are created EVERY time the page loads!), and therefore your dynamicEventHandler now has a context from which to execute.

Here is the corrected code (but as a single file with embedded VB for simplicity, you could of course separate this out into a codebehind file):

<%@ Page Language="VB" AutoEventWireup="false" %>

<script runat="server">
    Dim numOfDesiredControls As Int16

    Protected Sub Page_Load() Handles form1.Load

        Try
            numOfDesiredControls = Convert.ToInt16(txtEnter.Text)
            If Not numOfDesiredControls = 0 Then
                For i As Int16 = 1 To numOfDesiredControls
                    Dim txtTest As New TextBox
                    txtTest.Text = "dynamicTextBox"
                    txtTest.ID = "dynamicTextBox" + i.ToString
                    txtTest.AutoPostBack = True
                    ' txtTest.EnableViewState = False
                    Form.Controls.Add(txtTest)
                    AddHandler txtTest.TextChanged, AddressOf dynamicEventHandler
                Next
            End If
        Catch ex As Exception

        End Try
    End Sub

    Protected Sub dynamicEventHandler(ByVal sender As Object, ByVal e As System.EventArgs)
        ' If the event handler gets fired, reflect this by changing the text of lblConfirm
        Dim txt As TextBox
        txt = CType(sender, TextBox)
        lblConfirm.Visible = True
        lblConfirm.Text = "Event handler " + txt.Id + " fired: " + txt.Text ' append ID and text so we know which one fired it.
    End Sub
</script>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
        <div id="dynamicControlDiv">
            <asp:Label ID="lblEnter" runat="server" Text="Enter the amount of textboxes you want:"></asp:Label>
            <asp:TextBox ID="txtEnter" runat="server" AutoPostBack="true"></asp:TextBox>
            <asp:Label ID="lblConfirm" runat="server" Text=""></asp:Label>
        </div>
    </form>
</body>
</html>

Here is a starting point from Msft about dynamic controls that explains the behavior. There are a lot of resources out there for this.

http://msdn.microsoft.com/en-us/library/hbdfdyh7.aspx

Pro-tip: don't use dynamic controls if you can help it. While this is arguably a decent way to support browsers that do not use JavaScript, these days the preferred approach is to build the controls dynamically with JavaScript and use AJAX to do updates. Otherwise, you are sending way more data than you need to. When you use PostBack, every time you you POST back to the server you are (1) uploading the entire ViewState PLUS the form data to the server, (2) rebuilding the entire page (parsing ViewState, rendering HTML, etc.) on the server, and (3) sending all the HTML (and ViewState) back to the client. This is especially troublesome for mobile devices where power usage and data plan rates apply.

Question 2

You will need to set the AutoPostback property of the dynamic textboxes to True for them to fire their TextChanged event.

Protected Overrides Sub OnInit(ByVal e As System.EventArgs)
    MyBase.OnInit(e)

    For i As Int16 = 0 To 5
        Dim txtTest As New TextBox
        txtTest.Text = "this is an OnInit generated textbox"
        txtTest.ID = "testOnInit" + i.ToString
        txtTest.AutoPostBack = True  
        Form.Controls.Add(txtTest)
        AddHandler txtTest.TextChanged, AddressOf txtTest_TextChanged
    Next
End Sub

Protected Sub txtTest_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim txt As TextBox = DirectCast(sender, TextBox)
    lblTest.Text = txt.ID & " value changed to " & txt.Text
End Sub