how to reference dynamically created control in asp.net 3.5 with VB
I'm writing a program that inserts controls onto a webform dynamically. Depending on a variable, I add either a textbox, a set of radio buttons, or a set of checkboxes. Later, after a user clicks a submit button I need to use the controls to determine if the user is submitting the correct answer, but when I try to reference the id of a control, I get "txtAnser is not declared. It may be inaccessible due to it's protections level.
Here is the .aspx page (it's the standard content page of a master page):
<%@ Page Title="" Language="VB" MasterPageFile="~/top.master" AutoEventWireup="false"
CodeFile="test_page.aspx.vb" Inherits="Default2" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="PageContent" Runat="Server">
<asp:SqlDataSource ID="sdsQuestionPuller" runat="server"
ConnectionString="<%$ ConnectionStrings:SchoolhouseConnectionString6 %>"
SelectCommand="SELECT QuestionText, AnswerType, PossibleAnswers, CorrectAnswers
FROM Questions WHERE (SubjectID = @SubjectID) AND (QuestionOrder = @QuestionOrder)">
<SelectParameters>
<asp:SessionParameter Name="SubjectID" SessionField="SubjectID" />
<asp:SessionParameter Name="QuestionOrder" SessionField="PageNumber" />
</SelectParameters>
</asp:SqlDataSource>
<asp:SqlDataSource ID="sdsMaxQuestions" runat="server"
ConnectionString="<%$ ConnectionStrings:SchoolhouseConnectionString7 %>"
SelectCommand="SELECT MAX(QuestionOrder) AS LastQuestion FROM Questions GROUP BY SubjectID HAVING (SubjectID = @SubjectID)">
<SelectParameters>
<asp:SessionParameter Name="SubjectID" SessionField="SubjectID" />
</SelectParameters>
</asp:SqlDataSource>
<div>
<asp:Label ID="lblInstructionHolder" runat="server"></asp:Label>
</div>
<div>
<asp:Label ID="lblQuestionHolder" runat="server"></asp:Label>
</div>
<asp:PlaceHolder ID="plhQuestionHolder" runat="server"></asp:PlaceHolder>
<div>
<asp:Button ID="btnSubmit" Text="Submit" runat="server" />
</div>
</asp:Content>
And here is the code behind, I'm running into problems in the submit button click event where I try to reference the txtAnswer control in the select case statement:
Imports System.Data
Partial Class Default2
Inherits System.Web.UI.Page
Dim intMaxPage As Integer
'QuestionText, AnswerType, PossibleAnswers, CorrectAnswers
Dim strQuestion As String
Dim strQuestionType As String
Dim astrPossibleAnswers() As String
Dim intNumberOfPossAnswers As Integer
Dim astrCorrectAnswers() As String
Dim intNumberOfCorrectAnswers As Integer
Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
End Sub
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
'Load up the variables(make sure data is retrieved, create a view from the source, retrieve the only row, assing the item(s) from the row to variables)
sdsMaxQuestions.DataBind()
Dim dtvLastPageView As DataView = CType(sdsMaxQuestions.Select(DataSourceSelectArguments.Empty), DataView)
Dim dtrLastPageRow As DataRowView = dtvLastPageView.Item(0)
intMaxPage = CInt(Trim(dtrLastPageRow.Item(0).ToString))
Dim dtvQuestionsView As DataView = CType(sdsQuestionPuller.Select(DataSourceSelectArguments.Empty), DataView)
Dim dtrQuestionsRow As DataRowView = dtvQuestionsView.Item(0)
strQuestion = Trim(dtrQuestionsRow.Item(0).ToString)
strQuestionType = Trim(dtrQuestionsRow.Item(1).ToString)
astrPossibleAnswers = Split(Trim(dtrQuestionsRow.Item(2).ToString), ";")
intNumberOfPossAnswers = astrPossibleAnswers.Count
astrCorrectAnswers = Split(Trim(dtrQuestionsRow.Item(3).ToString), ";")
intNumberOfCorrectAnswers = astrCorrectAnswers.Count
'Finish loading controls
lblQuestionHolder.Text = strQuestion
Select Case strQuestionType
Case "checkbox"
lblInstructionHolder.Text = "Choose the correct answer(s)."
Case "radio"
lblInstructionHolder.Text = "Choose the best answer."
Case "fillintheblank"
lblInstructionHolder.Text = "Please fill in the blank, case doesn't count, spelling does."
Case Else
lblInstructionHolder.Text = "Somethings wrong, contact admin"
End Select
'Generate the controls for answers...
GenerateControls()
End Sub
Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
'Declare the variables, get any existing values, then check to see if the answer is correct, display a message and go to the next page or store the score.
Dim intNumberRight As Integer = 0
Dim intNumberTotal As Integer = 0
If Not (Session("NumberRight") = Nothing) Then
intNumberRight = CInt(Session("NumberRight"))
End If
If Not (Session("NumberTotal") = Nothing) Then
intNumberTotal = CInt(Session("NumberTotal"))
End If
Select Case strQuestionType
Case "checkbox"
Case "radio"
Case "fillintheblank"
'Here is where I am having issues
If txtAnswer Is Not Nothing Then
End If
If txtAnswer.text.ToLower = astrCorrectAnswers(0).ToLower Then
End If
Case Else
MsgBox("Somethings wrong, contact admin")
End Select
If intMaxPage = CType(Session("PageNumber"), Integer) Then
Response.Redirect("user_landing.aspx")
Else
Session("PageNumber") = CType(Session("PageNumber"), Integer) + 1
Response.Redirect("test_page.aspx")
End If
End Sub
Private Sub GenerateControls()
'Make the correct controls depending on the type
Dim conDivHolder As HtmlGenericControl = New HtmlGenericControl("div")
Select Case strQuestionType
Case "checkbox"
For i As Integer = 0 To intNumberOfPossAnswers - 1
Dim chkAnswer As CheckBox = New CheckBox
With chkAnswer
.ID = "chkAnswer" + i.ToString
.Text = astrPossibleAnswers(i)
End With
conDivHolder.Controls.Add(chkAnswer)
Next
Case "radio"
For i As Integer = 0 To intNumberOfPossAnswers - 1
Dim rdoAnswer As RadioButton = New RadioButton
With rdoAnswer
.ID = "rdoAnswer" + i.ToString
.Text = astrPossibleAnswers(i)
.GroupName = "rdoGroup"
End With
conDivHolder.Controls.Add(rdoAnswer)
Next
Case "fillintheblank"
Dim txtAnswer As TextBox = New TextBox
txtAnswer.ID = "txtAnswer"
conDivHolder.Controls.Add(txtAnswer)
Case Else
Dim lblOops As Label = New Label
lblOops.Text = "Oops, contact admin"
conDivHolder.Controls.Add(lblOops)
End Select
plhQuestionHolder.Controls.Add(conDivHolder)
End Sub
End Class
If anyone could point out what I need to do, I would appreciate it.
Thanks, Simon
Answer
First of all, you're generating your controls on Page_Load (PostBack or not), so whatever the state of txtAnswer was before the submit button was clicked, it's gone now - txtAnswer has been regenerated again with an initial state. You should dynamically render your controls only if IsPostBack is false.
Secondly, you should probably be accessing the txtAnswer's Text property within the Is Not Nothing if statement block. Otherwise you may get a null reference exception.
Thirdly, to get a reference to your TextBox control you can try to find the control by ID within its placeholder, with something like this (I'm doing this in C# - you can translate to VB on your own):
Define function to look for a control recursively:
protected Control FindControl(Control parent, string controlID)
{
Control control = parent.FindControlByID("controlID");
if (control != null)
{
return control;
}
foreach(Control child in control.Controls)
{
Control childControl = FindControl(child , controlID);
if (childControl != null)
{
return childControl;
}
}
return null;
}
Call your recursive find function:
Control ctrl = FindControl(plhQuestionHolder, "txtAnswer");
None of this code is actually tested, so don't yell at me if it doesn't work as is. This is merely a guide.