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vb.net - VB.Net - 如何让 DropDownList 根据 URL 查询字符串自动选择数据？

问题描述

在我的 Web 表单中，我的下拉列表已经包含加载数据选择的代码。现在我想根据 URL 中的查询字符串添加一个自动填充功能。

Private Sub FillLine() '1st dropdown

    '1. Load intial selection into drop down list (OK)
    '----------------------------------------------------------------------------------------------------
    Dim dt As New DataTable
    Dim strSql = "select distinct level1_id, [LCODE1]+ ' | '+[LNAME1] as [LCODE1]" _
                      & " FROM [SQLIOT].[dbo].[ZVIEW_MCM_LEVEL_LOOKUP]"
    Using conn As New SqlConnection(ConStr),
        cmd As New SqlCommand(strSql, conn)
        conn.Open()
        dt.Load(cmd.ExecuteReader)
    End Using
    If dt.Rows.Count > 0 Then
        line.DataSource = dt
        line.DataTextField = "LCODE1"
        line.DataValueField = "level1_id"
        line.DataBind()
        line.Items.Insert(0, "")
    End If
    '----------------------------------------------------------------------------------------------------


    '2. Pick out the value in drop down list based on URL query string (NG)
    '----------------------------------------------------------------------------------------------------
    Dim LID As String = Request.QueryString("LID")

    If LID <> Nothing Then

        LID3.Text = LID

        If Not IsPostBack() Then

            Dim cmdLID As New SqlCommand("select distinct [LCODE1]+ ' | '+[LNAME1] as [LCODE1] " _
                                         & "FROM [SQLIOT].[dbo].[ZVIEW_MCM_LEVEL_LOOKUP] " _
                                         & "where [LEVEL3_ID] = '" & LID3.Text & "'", conn)

            conn.Open()

            Dim rdr As SqlDataReader = cmdLID.ExecuteReader

            While rdr.Read

                line.Text = rdr("LCODE1")

            End While

            conn.Close()

        End If

    End If
    '----------------------------------------------------------------------------------------------------

End Sub

 Protected Sub line_selectedindexchanged(ByVal sender As Object, ByVal e As EventArgs)

    Try

        Dim level1_ID As Integer = Convert.ToInt32(line.SelectedValue.ToString())

        Dim value As Integer = Integer.Parse(level1_ID)

        FillProcess(level1_ID)

    Catch ex As Exception

        Console.WriteLine(ex)

    End Try
    'FillProcess(level1_ID)

End Sub

在测试期间，我的代码的第 1 部分很好。但是，在第 2 部分中，每次我LID在 URL 中输入查询字符串并刷新页面时，该值都不会显示在我的下拉列表中。

这里可能是什么问题？

标签： vb.netvisual-web-developer-2010

解决方案

我正在使用我的一个数据库进行测试。第 1 部分与您的代码相同。

第 2 部分
无需再次访问数据库。您需要的值在 DropDownList 中。我对 LID 使用硬编码值进行测试，但只需替换您的查询字符串值。循环遍历列表中的项目，直到找到您要查找的值。

Private Sub FillDropDownList()
    '1. Load intial selection into drop down list (OK)
    Dim dt As New DataTable
    Using cn As New SqlConnection(My.Settings.CoffeeConnection),
            cmd As New SqlCommand("Select Top 10 ID, Name From Coffees", cn)
        cn.Open()
        dt.Load(cmd.ExecuteReader)
    End Using
    DropDownList1.DataTextField = "Name"
    DropDownList1.DataValueField = "ID"
    DropDownList1.DataSource = dt
    DropDownList1.DataBind()
    '2. Pick out the value in drop down list based on URL query string 
    Dim LID As String = "14" 'Request.QueryString("LID")
    For Each item As ListItem In DropDownList1.Items
        If item.Value = LID Then
            item.Selected = True
            Exit For
        End If
    Next
End Sub

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