VB.Net - How to get DropDownList to auto select data based on URL query string?

Question

In my web form, my drop down list already have the code to load the data selection. Now I want to add an auto fill function based on the query string in URL.

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

During testing, part 1 of my code is fine. However, in part 2, every time I input the LID query string in my URL and refresh the page, the value won't show in my drop down list.

What may be the issue here?

score 0 · Answer 1 · answered Sep 19 '20 at 06:59

I am using one of my databases to test. Part 1 is the same as your code.

Part 2
It is not necessary to hit the database again. The values you need are in the DropDownList. I use a hard coded value for LID for testing but just substitute your query string value. Loop through the items in the list until you find the value you are looking for.

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

Thanks. But the code doesn't look like its working... I even hard coded the LID value like you did and still got no value. I should also mention that there are other dropdownlists in my form that are cascading, each new list is based on the list before it. Neither of them are working. — hjh93, Sep 21 '20 at 00:31

VB.Net - How to get DropDownList to auto select data based on URL query string?

1 Answers1