Question

我正在尝试动态创建一个页面，但是我第一次进入了这个页面。我在阅读后可以创建以下博客/帖子/文章。我遇到的问题是，当我点击第一个按钮时，我没有发生任何事情，如果我再点击它就可以了。

任何人都可以告诉我哪里出错了吗？

由于

ASP页面：

<%@ Page Title="Create / Amend Quotes" Language="vb" AutoEventWireup="false" CodeBehind="Quote.aspx.vb" Inherits="BIS.Quote" %>

 <!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 id="Head1" runat="server">
     <title></title>
 </head>
 <body>

    <form id="form1" runat="server">
     <div>
         <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>     

    </div>
     </form>
 </body>
 </html>

VB

Imports System.Data
 Imports System.Data.SqlClient
 Public Class Quote
     Inherits System.Web.UI.Page

    Const CREATE_SELECTION As String = "create"
     Const AMEND_SELECTION As String = "amend"
     Const VIEWSTATEKEY_DYNCONTROL As String = "VS_Controls"

    Protected Property VS_Controls() As String
         Get
             Dim result As String = ViewState.Item(VIEWSTATEKEY_DYNCONTROL)
             If result Is Nothing Then
                 Return String.Empty
             Else
                 Return result
             End If
         End Get
         Set(ByVal value As String)
             ViewState.Item(VIEWSTATEKEY_DYNCONTROL) = value
         End Set

    End Property

    Private Sub Quote_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
         PlaceHolder1.Controls.Clear()

    End Sub

    Private Sub Quote_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        Select Case Me.VS_Controls
             Case CREATE_SELECTION
                 Dim Lab As New Label
                 Lab.ID = "Tester"
                 Lab.Text = "Create"
                 Me.PlaceHolder1.Controls.Add(Lab)

            Case AMEND_SELECTION
                 Dim Lab As New Label
                 Lab.ID = "Tester_2"
                 Lab.Text = "Amend"
                 Me.PlaceHolder1.Controls.Add(Lab)

            Case Else
                 Dim btn_create As New Button
                 Dim btn_Amend As New Button
                 Dim Label1 As New Label

                btn_create.ID = "but_Create"
                 btn_create.Text = "Create"
                 btn_create.CommandName = "Create"
                 AddHandler btn_create.Click, AddressOf onClick

                btn_Amend.ID = "but_Amend"
                 btn_Amend.Text = "Amend"
                 btn_Amend.CommandName = "Amend"
                 AddHandler btn_Amend.Click, AddressOf onClick

                Label1.id = "lab1"

                Label1.Text = VS_Controls

                Me.PlaceHolder1.Controls.Add(btn_create)
                 Me.PlaceHolder1.Controls.Add(New LiteralControl(" ")) 'space them out
                 Me.PlaceHolder1.Controls.Add(btn_Amend)
                 Me.PlaceHolder1.Controls.Add(New LiteralControl(" ")) 'space them out
                 Me.PlaceHolder1.Controls.Add(Label1)
         End Select

    End Sub

    Private Sub onClick(ByVal sender As Object, ByVal e As EventArgs)

        Dim From As Button = DirectCast(sender, Button)
         Dim But_String As String = From.ID

        If But_String = "but_Create" Then
             Me.VS_Controls = CREATE_SELECTION
             ' Me.VS_Controls = "create"
             ' ViewState("create_amend") = "create"
         ElseIf But_String = "but_Amend" Then
             Me.VS_Controls = AMEND_SELECTION
             'ViewState("create_amend") = "amend"
         End If

    End Sub

    Private Sub Quote_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender





    End Sub
 End Class

Answer 1

在ASP.NET页面生命周期（http://msdn.microsoft.com/en-us/library/ms178472.aspx）中，Page_Load在事件处理之前发生。因此，在创建标签之前，您的视图状态不会被修改。你应该用你的逻辑来创建Page_PreRender中的标签（或者可以从点击事件中调用的单独方法，或者如果Page_Load为假则从IsPostback调用。）

Answer 2

你需要检查页面是否处于回发模式.....

if(!Page.IsPostBack){}

Answer 3

创建按钮并在OnInit期间分配事件处理程序。在您点击Page_Load时已经加载了ViewState。

动态创建按钮需要2次单击才能返回视图状态

3 个答案: