我正在编写一个程序，可以动态地将控件插入到webform中。根据变量，我添加一个文本框，一组单选按钮或一组复选框。之后，在用户单击提交按钮后，我需要使用控件来确定用户是否正在提交正确的答案，但是当我尝试引用控件的id时，我得到“txtAnser未声明。它可能无法访问由于它的保护水平。
这是.aspx页面（它是母版页的标准内容页面）：
<%@ 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>
这是后面的代码，我在提交按钮单击事件中遇到问题，我尝试在select case语句中引用txtAnswer控件：
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
如果有人能够指出我需要做什么，我将不胜感激。
谢谢， 西蒙
答案 0 :(得分：1)
您将不得不在占位符上执行递归FindControl以获取对动态控件的引用。试试这个
Public Shared Function FindChildControl(start As Control, id As String) As Control
If start IsNot Nothing Then
Dim foundControl As Control
foundControl = start.FindControl(id)
If foundControl IsNot Nothing Then
Return foundControl
End If
For Each c As Control In start.Controls
foundControl = FindChildControl(c, id)
If foundControl IsNot Nothing Then
Return foundControl
End If
Next
End If
Return Nothing
End Function
并致电
txtAnswer = FindChildControl(plhQuestionHolder, "txtAnswer")
If txtAnswer Is Not Nothing Then
End If
答案 1 :(得分：1)
首先，你在Page_Load（PostBack与否）上生成你的控件，所以无论txtAnswer的状态是什么，在点击提交按钮之前，它已经消失 - txtAnswer已经以初始状态再次重新生成。仅当IsPostBack为false时，才应动态呈现控件。
其次，您可能应该在Is Not Nothing if语句块中访问txtAnswer的Text属性。否则，您可能会得到一个空引用异常。
第三，为了获得对TextBox控件的引用，你可以尝试在其占位符中通过ID找到控件，使用类似的东西（我在C＃中这样做 - 你可以自己翻译成VB）：< / p>
定义函数以递归方式查找控件：
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;
}
调用递归查找函数：
Control ctrl = FindControl(plhQuestionHolder, "txtAnswer");
这些代码都没有经过实际测试，所以如果它不能正常工作，请不要对我大喊大叫。这只是一个指南。