asp.net - 在下拉列表中创建第一项“--select--”

Question

我想让我的下拉列表在第一次加载页面时选择第一个值“--select--”，因为我需要强制用户从列表中选择一个事件。我很模糊，因为我需要在 page_load 执行其他功能来检查复选框启用属性，所以我不确定应该将编码放在哪里，以将空值添加到下拉列表。

我确实在页面加载中放入了以下代码，但没有任何反应，“-select-”也没有出现在下拉列表中。

If Not Page.IsPostBack Then

        ddlEventTitle.Items.Insert(0, New ListItem("-select-", String.Empty))

    End If

我应该怎么做才能修改我的编码？

客户端代码：

<%@ Page Language="VB" MasterPageFile="~/MasterPageAdmin.master" AutoEventWireup="false" CodeFile="addbooth.aspx.vb" Inherits="addbooth" title="Untitled Page" %>
<%@ Register assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagprefix="asp" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>

<asp:Content ID="ContentPlaceHolder2" runat="server" 
contentplaceholderid="ContentPlaceHolder2">

 <table class="style8" cellpadding="3">
 <tr>
 <td class="style9">Add New Booth</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td class="style9">&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td class="style9">Event Title:</td>
 <td>
 <asp:SqlDataSource ID="SqlDataSourceEventTitle" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString1 %>" SelectCommand="SELECT DISTINCT [eventID], [eventTitle] FROM [eventinfo]">
 </asp:SqlDataSource>
 <asp:DropDownList ID="ddlEventTitle" runat="server" DataSourceID="SqlDataSourceEventTitle" DataTextField="eventTitle" DataValueField="eventID" Width="240px" AutoPostBack="True">
 </asp:DropDownList>
 </td>
 </tr>
 <tr>
 <td class="style9">Booth Alias:</td>
 <td>
 <asp:TextBox ID="txtBoothAlias" runat="server" Width="235px"></asp:TextBox>
 </td>
 </tr>
 <tr>
 <td class="style9"> Booth Type:</td>
 <td>
 <asp:DropDownList ID="ddlBoothType" runat="server" Width="240px" AutoPostBack="True">
 <asp:ListItem Value="7">8&#39;x8&#39;</asp:ListItem>
 <asp:ListItem Value="10">9&#39;x8&#39;</asp:ListItem>
 <asp:ListItem Value="11">12&#39;x50&#39;</asp:ListItem>
 <asp:ListItem Value="12">16&#39;x10&#39;</asp:ListItem>
 <asp:ListItem Value="13">20&#39;x16&#39;</asp:ListItem>
 <asp:ListItem Value="15">32&#39;x10&#39;</asp:ListItem>
 <asp:ListItem Value="17">32&#39;x14.5&#39;</asp:ListItem>
 </asp:DropDownList>
 </td>
 </tr>
 <tr>
 <td class="style10" valign="top" colspan="2">Booth Duration:<br />
 <font size="2">Tick to activate availability</font></td>
 </tr>
 <tr>
 <td class="style10" valign="top" colspan="2" align="center">
 <asp:Panel ID="Panel1" runat="server" Width="328px" Direction="LeftToRight" HorizontalAlign="Center">
 <table cellpadding="5" class="style8">
 <tr>
 <td>
 <asp:CheckBox ID="cbWeek1" runat="server" Text="Week 1" TextAlign="Left" OnCheckedChanged="cbWeek1_CheckedChanged" AutoPostBack="true"/>
  </td>
  <td>
 <asp:CheckBox ID="cbWeek2" runat="server" Text="Week 2" TextAlign="Left" OnCheckedChanged="cbWeek2_CheckedChanged" AutoPostBack="true"/>
   </td>
   <td>
  <asp:CheckBox ID="cbWeek3" runat="server" Text="Week 3" TextAlign="Left" OnCheckedChanged="cbWeek3_CheckedChanged" AutoPostBack="true"/>
   </td>
    <td>
 <asp:CheckBox ID="cbWeek4" runat="server" Text="Week 4" TextAlign="Left" OnCheckedChanged="cbWeek4_CheckedChanged" AutoPostBack="true"/>
                                                                                </td>
                                                                            </tr>
                                                                            <tr>
                                                                                <td>
                                                                                             <asp:CheckBox ID="cbWeek5" runat="server" Text="Week 5" TextAlign="Left" OnCheckedChanged="cbWeek5_CheckedChanged" AutoPostBack="true"/>
                                                                                </td>
                                                                                <td>
                                                                                              <asp:CheckBox ID="cbWeek6" runat="server" Text="Week 6" TextAlign="Left" OnCheckedChanged="cbWeek6_CheckedChanged" AutoPostBack="true"/>
                                                                                </td>
                                                                                <td>
                                                                                              <asp:CheckBox ID="cbWeek7" runat="server" Text="Week 7" TextAlign="Left" OnCheckedChanged="cbWeek7_CheckedChanged" AutoPostBack="true"/>
                                                                                </td>
                                                                                <td>
                                                                                              <asp:CheckBox ID="cbWeek8" runat="server" Text="Week 8" TextAlign="Left" OnCheckedChanged="cbWeek8_CheckedChanged" AutoPostBack="true"/>
                                                                                </td>
                                                                            </tr>
                                                                        </table>

  </asp:Panel>
  <asp:RoundedCornersExtender ID="Panel1_RoundedCornersExtender"runat="server" Enabled="True" TargetControlID="Panel1" BorderColor="CadetBlue" Color="ButtonFace">
 </asp:RoundedCornersExtender>
       </td>
       </tr>
       <tr>
        <td class="style11">
         </td>
         <td class="style11">
 <asp:Button ID="ButtonAddNewBooth" runat="server" Text="Add New Booth"  Height="50px" />
 </td>
 </tr>
   <tr>
    <td class="style9"> &nbsp;</td>
     <td>&nbsp;</td>
       </tr>
         <tr>
 <td class="style9" colspan="2">
 <asp:GridView ID="GridViewBoothAdded" runat="server" AutoGenerateColumns="False" CellPadding="4" DataSourceID="SqlDataSourceBoothAdded" Font-Size="Small" ForeColor="#333333" GridLines="None" AllowPaging="True" PageSize="5" Visible="False">
 <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
 <Columns>
  <asp:BoundField DataField="boothAlias" HeaderText="Booth Alias" SortExpression="boothAlias" />
 <asp:BoundField DataField="week1" HeaderText="week1" SortExpression="week1" />
 <asp:BoundField DataField="week2" HeaderText="week2" SortExpression="week2" />
 <asp:BoundField DataField="week3" HeaderText="week3" SortExpression="week3" />
 <asp:BoundField DataField="week4" HeaderText="week4" SortExpression="week4" />
 <asp:BoundField DataField="week5" HeaderText="week5" SortExpression="week5" />
 <asp:BoundField DataField="week6" HeaderText="week6" SortExpression="week6" />
 <asp:BoundField DataField="week7" HeaderText="week7" SortExpression="week7" />
 <asp:BoundField DataField="week8" HeaderText="week8" SortExpression="week8" />
  </Columns>
  <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
  <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
  <EmptyDataTemplate>
        No booth record
  </EmptyDataTemplate>
  <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
  <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" Font-Size="Small" ForeColor="White" />
  <EditRowStyle BackColor="#999999" />
  <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
   </asp:GridView>
   <asp:RoundedCornersExtender ID="GridViewBoothAdded_RoundedCornersExtender" runat="server" Enabled="True" TargetControlID="GridViewBoothAdded">
    </asp:RoundedCornersExtender>
    <asp:SqlDataSource ID="SqlDataSourceBoothAdded" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString1 %>" 
    SelectCommand="SELECT [week1], [week2], [week3], [week4], [week5], [week6], [week7], [week8], [eventID], [boothAlias], [eventTitle] FROM [booth_eventinfo] WHERE ([eventID] = @eventID)">
   <SelectParameters>
    <asp:ControlParameter ControlID="ddlEventTitle" Name="eventID" PropertyName="SelectedValue" Type="Int32" />
   </SelectParameters>
   </asp:SqlDataSource>
                                                                </td>
                                                            </tr>
   </table>

服务器代码：

Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Threading
Imports System.Object
Partial Class addbooth
Inherits System.Web.UI.Page

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    If Not Page.IsPostBack Then

        ddlEventTitle.Items.Insert(0, New ListItem("-select-", String.Empty))

    End If

    Dim eventID As String = ddlEventTitle.SelectedValue
    Dim connString As String = ConfigurationManager.ConnectionStrings("ConnectionString1").ConnectionString
    ' Dim connString As String = "Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\CikguTube3.mdf;Integrated Security=True;User Instance=True"
    Dim con As SqlConnection = New SqlConnection(connString)

    Dim cmdQuery As String = "SELECT * FROM eventinfo WHERE eventID = '" + eventID + "'"
    Dim cmd As SqlCommand = New SqlCommand(cmdQuery)
    Dim myReader As SqlDataReader


    cmd.Connection = con
    cmd.CommandType = CommandType.Text
    con.Open()

    myReader = cmd.ExecuteReader()

    While myReader.Read()

        Label1.Text = myReader("totalDay").ToString()

    End While

    myReader.Close()

    cmd.ExecuteNonQuery()
    cmd.Parameters.Clear()
    con.Close()

    If Label1.Text = "7" Then
        cbWeek1.Enabled = True
        cbWeek2.Enabled = False
        cbWeek3.Enabled = False
        cbWeek4.Enabled = False
        cbWeek5.Enabled = False
        cbWeek6.Enabled = False
        cbWeek7.Enabled = False
        cbWeek8.Enabled = False

    ElseIf Label1.Text = "14" Then

        cbWeek1.Enabled = True
        cbWeek2.Enabled = True
        cbWeek3.Enabled = False
        cbWeek4.Enabled = False
        cbWeek5.Enabled = False
        cbWeek6.Enabled = False
        cbWeek7.Enabled = False
        cbWeek8.Enabled = False

    End If


End Sub


Protected Sub ButtonAddNewBooth_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles ButtonAddNewBooth.Click



    Dim connString As String = ConfigurationManager.ConnectionStrings("ConnectionString1").ConnectionString
    '"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\eventdb.mdf;Integrated Security=True;User Instance=True"
    Dim con As SqlConnection = New SqlConnection(connString)


    Dim cmdQuery As String = "INSERT INTO booth(eventID,boothAlias,boothType,week1,week2,week3,week4,week5,week6,week7,week8) VALUES (@eventID,@boothAlias,@boothType,@week1,@week2,@week3,@week4,@week5,@week6,@week7,@week8)"

    Dim cmd = New SqlCommand(cmdQuery)
    cmd.Connection = con
    cmd.CommandType = CommandType.Text
    con.Open()
    cmd.Parameters.AddWithValue("@eventID", ddlEventTitle.SelectedValue)
    cmd.Parameters.AddWithValue("@boothAlias", txtBoothAlias.Text)
    cmd.Parameters.AddWithValue("@boothType", ddlBoothType.SelectedValue)



    If (cbWeek1.Checked = True) Then
        cmd.Parameters.AddWithValue("@week1", "1")
    Else
        cmd.Parameters.AddWithValue("@week1", "0")
    End If

    If (cbWeek2.Checked = True) Then
        cmd.Parameters.AddWithValue("@week2", "1")
    Else
        cmd.Parameters.AddWithValue("@week2", "0")
    End If

    If (cbWeek3.Checked = True) Then
        cmd.Parameters.AddWithValue("@week3", "1")
    Else
        cmd.Parameters.AddWithValue("@week3", "0")
    End If

    If (cbWeek4.Checked = True) Then
        cmd.Parameters.AddWithValue("@week4", "1")
    Else
        cmd.Parameters.AddWithValue("@week4", "0")
    End If

    If (cbWeek5.Checked = True) Then
        cmd.Parameters.AddWithValue("@week5", "1")
    Else
        cmd.Parameters.AddWithValue("@week5", "0")
    End If

    If (cbWeek6.Checked = True) Then
        cmd.Parameters.AddWithValue("@week6", "1")
    Else
        cmd.Parameters.AddWithValue("@week6", "0")
    End If

    If (cbWeek7.Checked = True) Then
        cmd.Parameters.AddWithValue("@week7", "1")
    Else
        cmd.Parameters.AddWithValue("@week7", "0")
    End If

    If (cbWeek8.Checked = True) Then
        cmd.Parameters.AddWithValue("@week8", "1")
    Else
        cmd.Parameters.AddWithValue("@week8", "0")
    End If


    GridViewBoothAdded.DataBind()

    cmd.ExecuteNonQuery()
    cmd.Parameters.Clear()
    con.Close()





End Sub

End Class

Answer 1

我不喜欢编写这样的代码。就我个人而言，我不喜欢将与数据库相关的信息和查询保存在 aspx 文件中。我会将该代码移动到代码隐藏文件中的函数中。

所以我会像这样更新我的 UI（.aspx 文件）。只是简单的下拉列表声明

<asp:DropDownList ID="ddlEventTitle" runat="server"></asp:DropDownList>

在你后面的代码中，写一个这样的方法

Private Sub LoadEvents()

    Dim cmdString As String = "SELECT DISTINCT eventID, eventTitle FROM eventinfo"
    Dim connStr As String = "Data Source=Localhost\SQLEXPRESS;Initial Catalog=Flash2;Integrated Security=True;"
    Using conn As New SqlConnection(connStr)
        conn.Open()
        Using cmd As New SqlCommand(cmdString, conn)
            Dim rdr As SqlDataReader = cmd.ExecuteReader()
            ddlEventTitle.DataValueField = "eventID"
            ddlEventTitle.DataTextField = "eventTitle"
            ddlEventTitle.DataSource = rdr
            ddlEventTitle.DataBind()
            ddlEventTitle.Items.Insert(0, New ListItem("Select Event", "0"))
        End Using
    End Using

End Sub

现在在页面加载事件中调用此方法

Protected Sub Page_Load(sender As Object, e As EventArgs)
    If Not IsPostBack Then
        LoadFromDataReader()
    End If
End Sub

这应该会为您带来带有事件的下拉列表，其中第一个元素“选择事件”的值为“0”。