Question

我正在VS 2008中开发一个VB.NET ASPX文件。但是我无法检索所选的输入参数。这是一个真正简单的问题。这是我目前的代码：

<html>
    <SCRIPT LANGUAGE="VB" RUNAT="Server">
        Sub Page_Load(ByVal Sender As Object, ByVal E As EventArgs)

            If Not IsPostBack Then
                Main()
            Else
                Main2()
                If part_transfer.Value.Trim() <> "" Then
                    ShowChart()
                    Panel1.Visible = False
                    Panel2.Visible = True
                End If
            End If

        End Sub

Sub Main() 
'*** Query database and get arrays for the chart and bind query results to datagrid  

Dim YearDate As Date = "1/1/2010"
Dim arrYear As New ArrayList()
While YearDate <= Today
arrYear.Add(YearDate.ToString("yyyy"))
YearDate = YearDate.AddYears(1)
End While

dYear.DataSource = arrYear
dYear.DataBind()
dYear.SelectedValue = Today.ToString("yyyy")

Dim ListMonth As Date = "1/1/2010"
Dim arrListMonth As New ArrayList()
While ListMonth <= "12/1/2010"
arrListMonth.Add(ListMonth.ToString("MMM"))
ListMonth = ListMonth.AddMonths(1)
End While

dEndMonth.DataSource = arrListMonth
dEndMonth.DataBind()

dEndMonth.SelectedValue = Today.ToString("MMM")

Response.Write("Main " & dEndMonth.SelectedValue & "<br>")...
        End Sub

        Sub Main2()
        '*** Query database and get arrays for the chart and bind query results to datagrid  
            Dim YearDate As Date = "1/1/2010"
            Dim arrYear As New ArrayList()

            Dim TextSearch As String 
            TextSearch = dTextSearch.Text

            While YearDate <= Today
                arrYear.Add(YearDate.ToString("yyyy"))
                YearDate = YearDate.AddYears(1)
            End While

            dYear.DataSource = arrYear
            dYear.DataBind()

            Dim ListMonth As Date = "1/1/2010"
            Dim arrListMonth As New ArrayList()
            While ListMonth <= "12/1/2010"
                arrListMonth.Add(ListMonth.ToString("MMM"))
                ListMonth = ListMonth.AddMonths(1)
            End While

            dEndMonth.DataSource = arrListMonth
            dEndMonth.DataBind()

            Response.Write("Main2 " & dEndMonth.SelectedValue & "<br>")
...
        <form runat="Server" method="post" id="Form1">
            <div style="font-size:18pt; font-family:verdana; font-weight:bold; color:#336699">
               Parts Watch List
            </div>
            <br />
             <br />
                    <table>
                <tr><th>Year</th><th>Ending Month</th></tr>
                <tr>
                    <td><ASP:DROPDOWNLIST id="dYear" runat="Server" autopostback="true" /></td>
                    <td><ASP:DROPDOWNLIST id="dEndMonth" runat="Server" autopostback="true" width="75"/></td>
                    <td><ASP:TEXTBOX id="dTextSearch" OnTextChanged="dBtn_TextChanged" columns="2" MaxLength="30" Text="" runat="Server" autopostback="true" Width="150" /></td>
                    <td><ASP:BUTTON id="dBtn" Text="Search" OnClick="dBtn_Click" runat="Server" autopostback="true" width="100"/></td>
                </tr>
            </table>

......这是一个非常基本的问题。此代码目前设置了我想要的下拉列表，但只是没有返回选定的月份和年份。我该如何解决这个问题？请注意，Main2 sub适用于PostBack = True。

Answer 1

您正在Main2（在PostBack中）绑定DropDownList。这可以防止触发事件并覆盖SelectedValue。

如果您再次在dEndMonth.SelectedValue之前查找DataBind，则会看到SelectedValue是正确的。

为什么不使用事件处理程序来处理SelectedIndexChanged - DropDownList事件而不是Main2 - 方法？

<ASP:DropDownList id="dEndMonth" OnSelectedIndexChanged="EndMonthChanged" autopostback="true" runat="Server" width="75"/></td>

和代码隐藏：

Protected Sub EndMonthChanged(sender as Object, e as EventArgs)
    Dim dEndMonth = DirectCast(sender, DropDownList)
    'get selected value etc. and DataBind it AFTERWARDS when needed or whatever...'
End Sub

您应该对用户的操作做出反应，而不是根据您认为用户可以做的事情做出反应，因此请使用事件处理程序。

如何实现VB.NET DropDownList？

1 个答案: