Question

我有这个代码可以根据第一个下拉列表填充第二个下拉列表（在页面的Page_Init事件中）：

Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    . . .
    'Populate the Units dropdown
    Dim unitsDT As DataTable
    sql = "Select distinct unit from masterunits where abs(active) = 1"
    retDS = sqlDAL.runSQLDataSet(sql)
    unitsDT = retDS.Tables(0)
    DropDownListUnits.DataSource = unitsDT
    DropDownListUnits.DataTextField = "unit"
    DropDownListUnits.DataValueField = "unit"
    DropDownListUnits.DataBind()

    'Populate the Members dropdown based on Unit selected
    'Dim selectedUnit As String = DropDownListUnits.Text
    Dim selectedUnit As String = DropDownListUnits.SelectedItem.Text
    Dim membersDT As DataTable
    sql = "select distinct shortname, M.memberno from members M left join memberunitproducts mup on M.MemberNo = mup.MemberNo where unit = '" + selectedUnit  + "' order by shortname"
    retDS = sqlDAL.runSQLDataSet(sql)
    membersDT = retDS.Tables(0)
    DropDownListMembers.DataSource = membersDT
    DropDownListMembers.DataTextField = "shortname"
    DropDownListMembers.DataValueField = "memberno"
    DropDownListMembers.DataBind()
    . . .
End Sub

...我需要在第一个下拉列表更改时更新第二个下拉列表，所以请输入以下代码：

Protected Sub DropDownListUnits_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownListUnits.SelectedIndexChanged

DropDownListMembers.Items.Clear
    DropDownListCustomers.Items.Clear

    Dim selectedUnit As String = DropDownListUnits.SelectedItem.Text

    Dim sqlDAL As New SQLServer(ConfigurationSettings.AppSettings("ConnectionString"))
    Dim membersDT As DataTable
    Dim retDS As DataSet
    Dim sql As String = "select distinct shortname, M.memberno from members M left join memberunitproducts mup on M.MemberNo = mup.MemberNo where unit = '" + selectedUnit  + "' order by shortname"
    retDS = sqlDAL.runSQLDataSet(sql)
    membersDT = retDS.Tables(0)

    DropDownListMembers.DataSource = membersDT
    DropDownListMembers.DataTextField = "shortname"
    DropDownListMembers.DataValueField = "memberno"
    DropDownListMembers.DataBind()
End Sub

...但它不起作用 - 从DropDownListUnits中选择一个不同的单位不会改变DropDownListMembers中的内容。

显然这是：

Dim selectedUnit As String = DropDownListUnits.SelectedItem.Text

...不会将从DropDownListUnits中选择的新值检索到selectedUnit。

我甚至添加了这个，用于调试目的：

Label2.Text = selectedUnit

...但Label2永远不会改变。

我在这里做错了什么？

更新

基于this，我也试过了：

Dim selectedUnit As String = DropDownListUnits.SelectedItem.ToString()

......但没有区别。

更新2

事件显然甚至没有开火。这段代码：

Protected Sub DropDownListUnits_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownListUnits.SelectedIndexChanged
        Label2.Text = "it fired"
        . . .

...显示Label2的文字没有变化......

更新3

当我尝试将其作为Page_Init事件的第一行时：

If Not IsPostBack Then Exit Sub

......它甚至没有运行一次。

我已经有类似的事情了：

Dim PageAlreadyInitted As Boolean = False

Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If PageAlreadyInitted = True Then Exit Sub
    PageAlreadyInitted = True
    . . .

更新4

根据最后的评论，我在Page_Init中尝试了这个：

If Page.IsPostBack = True Then Exit Sub

...并没有什么区别 - 我仍然没有得到DropDownListUnits_SelectedIndexChanged事件的结果;它显然没有被解雇，因为Label2没有改变为“它被解雇”，因为它应该：

Protected Sub DropDownListUnits_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownListUnits.SelectedIndexChanged
    Label2.Text = "it fired"

更新5

这比Keith Richards的头发从他的noggin的椰子树上掉下来后更加混乱：我试图访问下拉列表中显示的值，它给了我错误的价值。

以下是填充下拉列表的代码：

Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If PageAlreadyInitted = True Then Exit Sub
    If Page.IsPostBack = True Then Exit Sub
    PageAlreadyInitted = True

    Dim sqlDAL As New SQLServer(ConfigurationSettings.AppSettings("ConnectionString"))
    'Populate the Units dropdown
    Dim unitsDT As DataTable
    Dim sql As String = "Select distinct mu.unit from masterunits mu left join MasterUnitsProjSales mps on mps.Unit = mu.Unit where abs(active) = 1 and mps.NewBiz != 0 order by mu.unit"
    Dim retDS As DataSet = sqlDAL.runSQLDataSet(sql)
    unitsDT = retDS.Tables(0)
    DropDownListUnits.DataSource = unitsDT
    DropDownListUnits.DataTextField = "unit"
    DropDownListUnits.DataValueField = "unit"
    DropDownListUnits.DataBind()

    'Populate the Members dropdown - TODO: Call this when Unit changes, too
    Dim selectedUnit As String = DropDownListUnits.SelectedItem.Text
    Dim membersDT As DataTable
    sql = "select distinct shortname, M.memberno from members M left join memberunitproducts mup on M.MemberNo = mup.MemberNo where unit = '" + selectedUnit + "' order by shortname"
    retDS = sqlDAL.runSQLDataSet(sql)
    membersDT = retDS.Tables(0)
    DropDownListMembers.DataSource = membersDT
    DropDownListMembers.DataTextField = "shortname"
    DropDownListMembers.DataValueField = "memberno"
    DropDownListMembers.DataBind()

    'Populate the Customers dropdown - TODO: Call this when Member changes, too
    Dim selectedMember As String = DropDownListMembers.SelectedItem.Value
    Dim customersDT As DataTable
    sql = "select distinct companyname from customers C left join members M on M.MemberNo = C.MemberNo where M.MemberNo = '" + selectedMember + "' order by companyname"
    retDS = sqlDAL.runSQLDataSet(sql)
    customersDT = retDS.Tables(0)
    DropDownListCustomers.DataSource = customersDT
    DropDownListCustomers.DataTextField = "companyname"
    DropDownListCustomers.DataValueField = "companyname"
    DropDownListCustomers.DataBind()

    sqlDAL.Dispose()
End Sub

这就是我所看到的：

请注意，“Applebees”是显示的单位（我没有选择它 - 它是集合中的第一个项目，默认显示）。

然而，当我按下按钮时，存储在Unit的数据库中的值是“Abuelos”而不是“Applebees”。这不仅令人沮丧，而且极端奇怪，因为“Abuelos”甚至不存在于物品集合中：

以下是试图获取值的代码，用于更新和插入数据库中的记录：

Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim connStr As String = "SERVER=PROSQL05;DATABASE=cpsdata;UID=sa;PWD=sqlsql"
    Dim upd8DML As String = "UPDATE CustomerCategoryLog SET Category = 'Existing', EndDate = @DateTimeYesterday, ChangedOn = @CurrentDateTime WHERE Unit = @Unit And MemberNo = @MemberNo AND Custno = @CustNo"
    Dim insertDML As String = "INSERT INTO CustomerCategoryLog (MemberNo, Unit, Custno, Category, Subcategory, BeginDate, ChangedBy, ChangedOn) VALUES (@MemberNo_Insert, @Unit_Insert, @CustNo_Insert, @Category, @Subcategory, @BeginDate, @ChangedBy, @ChangedOn)"

    Dim coName As String
    Dim argVals(2) As String
    Dim _Unit As String
    Dim _MemberNo As String
    Dim _CustNo As String

    coName = DropDownListCustomers.SelectedItem.ToString()
    argVals = GetArgValsForCompanyName(coName)
    _Unit = argVals(0)
    _MemberNo = argVals(1)
    _CustNo = argVals(2)
    Using conn As New SqlConnection(connStr), _
            cmd As New SqlCommand(upd8DML, conn)
        cmd.Parameters.Add("@Unit", SqlDbType.VarChar, 50).Value = _Unit
        cmd.Parameters.Add("@MemberNo", SqlDbType.VarChar, 50).Value = _MemberNo
        cmd.Parameters.Add("@CustNo", SqlDbType.VarChar, 50).Value = _CustNo
        cmd.Parameters.Add("@DateTimeYesterday", SqlDbType.DateTime).Value = DateTime.Today.AddDays(-1)
        cmd.Parameters.Add("@CurrentDateTime", SqlDbType.DateTime).Value = Date.Now
        conn.Open()
        cmd.ExecuteScalar()
    End Using
    ' Now insert a new record with "Existing" categories and Now as the BeginDate
    Using conn As New SqlConnection(connStr), _
            cmd As New SqlCommand(insertDML, conn)
        cmd.Parameters.Add("@MemberNo_Insert", SqlDbType.VarChar, 50).Value = _MemberNo
        cmd.Parameters.Add("@Unit_Insert", SqlDbType.VarChar, 50).Value = _Unit
        cmd.Parameters.Add("@CustNo_Insert", SqlDbType.VarChar, 50).Value = _CustNo
        cmd.Parameters.Add("@Category", SqlDbType.VarChar, 50).Value = "Existing"
        cmd.Parameters.Add("@Subcategory", SqlDbType.VarChar, 50).Value = "Existing"
        cmd.Parameters.Add("@BeginDate", SqlDbType.DateTime).Value = DateTime.Today
        cmd.Parameters.Add("@ChangedBy", SqlDbType.VarChar, 50).Value = Environment.UserName
        cmd.Parameters.Add("@ChangedOn", SqlDbType.DateTime).Value = Date.Now
        conn.Open()
        cmd.ExecuteScalar()
    End Using
End Sub

这是在数据库中插入和更新的内容：

正如你所看到的，“Abuelos”是单位价值，虽然应该是“Applebees” - Hec Ramsey是什么！？！

Answer 1

这实际上确实有效：

_Unit = DropDownListUnits.SelectedItem.ToString() 
_MemberNo = DropDownListMembers.SelectedValue.ToString()
_CustNo = DropDownListCustomers.SelectedValue.ToString()

正在使用这些值更新/插入记录。在更多背景下：

Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim connStr As String = "SERVER=PROSQL05;DATABASE=cpsdata;UID=sa;PWD=sqlsql"
    Dim upd8DML As String = "UPDATE CustomerCategoryLog SET Category = 'Existing', EndDate = @DateTimeYesterday,

ChangedOn = @CurrentDateTime WHERE Unit = @Unit And MemberNo = @MemberNo AND Custno = @CustNo“ Dim insertDML As String =“INSERT INTO CustomerCategoryLog（MemberNo，Unit，Custno，Category，Subcategory， VALDES（@ MemberNo_Insert，@ Unit_Insert，@ CustomerNo_Insert，@ Category，@ Subcategory， @BeginDate，@ ChangedBy，@ ChangedOn）“

    Dim _Unit As String
    Dim _MemberNo As String
    Dim _CustNo As String

    _Unit = DropDownListUnits.SelectedItem.ToString() 
    _MemberNo = DropDownListMembers.SelectedValue.ToString()
    _CustNo = DropDownListCustomers.SelectedValue.ToString()
    Using conn As New SqlConnection(connStr), _
            cmd As New SqlCommand(upd8DML, conn)
        cmd.Parameters.Add("@Unit", SqlDbType.VarChar, 50).Value = _Unit
        cmd.Parameters.Add("@MemberNo", SqlDbType.VarChar, 50).Value = _MemberNo
        cmd.Parameters.Add("@CustNo", SqlDbType.VarChar, 50).Value = _CustNo
        cmd.Parameters.Add("@DateTimeYesterday", SqlDbType.DateTime).Value = DateTime.Today.AddDays(-1)
        cmd.Parameters.Add("@CurrentDateTime", SqlDbType.DateTime).Value = Date.Now
        conn.Open()
        cmd.ExecuteScalar()
    End Using
    ' Now insert a new record with "Existing" categories and Now as the BeginDate
    Using conn As New SqlConnection(connStr), _
            cmd As New SqlCommand(insertDML, conn)
        cmd.Parameters.Add("@MemberNo_Insert", SqlDbType.VarChar, 50).Value = _MemberNo
        cmd.Parameters.Add("@Unit_Insert", SqlDbType.VarChar, 50).Value = _Unit
        cmd.Parameters.Add("@CustNo_Insert", SqlDbType.VarChar, 50).Value = _CustNo
        cmd.Parameters.Add("@Category", SqlDbType.VarChar, 50).Value = "Existing"
        cmd.Parameters.Add("@Subcategory", SqlDbType.VarChar, 50).Value = "Existing"
        cmd.Parameters.Add("@BeginDate", SqlDbType.DateTime).Value = DateTime.Today
        cmd.Parameters.Add("@ChangedBy", SqlDbType.VarChar, 50).Value = Environment.UserName
        cmd.Parameters.Add("@ChangedOn", SqlDbType.DateTime).Value = Date.Now
        conn.Open()
        cmd.ExecuteScalar()
    End Using
End Sub

所以，得到显示的值如下：

_Unit = DropDownListUnits.SelectedItem.ToString()

...和数据值如下：

_MemberNo = DropDownListMembers.SelectedValue.ToString()
_CustNo = DropDownListCustomers.SelectedValue.ToString()

......确实有效。

我仍然（不同的问题）不能让第二个和第三个下拉列表根据第一个值的变化重新填充，但是... ...

Answer 2

您需要使用 If Not IsPostBack 在初始页面加载时填充DropDownListUnits 。否则，DropDownListUnits将在回发时填充新数据，并丢失所选值。

Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If Not IsPostBack . . . 'Populate the Units dropdown Dim unitsDT As DataTable sql = "Select distinct unit from masterunits where abs(active) = 1" retDS = sqlDAL.runSQLDataSet(sql) unitsDT = retDS.Tables(0) DropDownListUnits.DataSource = unitsDT DropDownListUnits.DataTextField = "unit" DropDownListUnits.DataValueField = "unit" DropDownListUnits.DataBind() . . . End If End Sub Protected Sub DropDownListUnits_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownListUnits.SelectedIndexChanged DropDownListMembers.Items.Clear DropDownListCustomers.Items.Clear Dim selectedUnit As String = DropDownListUnits.SelectedValue ^^^^^^ Dim sqlDAL As New SQLServer(ConfigurationSettings.AppSettings("ConnectionString")) Dim membersDT As DataTable Dim retDS As DataSet Dim sql As String = "select distinct shortname, M.memberno from members M left join memberunitproducts mup on M.MemberNo = mup.MemberNo where unit = '" + selectedUnit + "' order by shortname" retDS = sqlDAL.runSQLDataSet(sql) membersDT = retDS.Tables(0) DropDownListMembers.DataSource = membersDT DropDownListMembers.DataTextField = "shortname" DropDownListMembers.DataValueField = "memberno" DropDownListMembers.DataBind() End Sub

如何在下拉列表中访问所选项目的值？

更新

更新2

更新3

更新4

更新5

2 个答案: