VB asp.net：我想从数据库中添加一些数据到下拉列表中

Question

i want to add some data into dropdownlist from database and don't have duplicate data, so i did this ~

 Dim ads As New Web.UI.WebControls.AccessDataSource
        ads.DataFile = "~/app_data/board.mdb"
        ads.SelectCommand = "SELECT DISTINCT [photo_species] FROM [phototable]"
        Dim dv As DataView = ads.Select(New DataSourceSelectArguments)
        For i = 0 To dv.Count - 1
            DropDownList1.Items.Add(dv.Item(0).Row("photo_species"))
        Next

but when i run the code it shows the same data again and again

Answer 1

Change the 0 in this line:

DropDownList1.Items.Add(dv.Item(0).Row("photo_species"))

to i:

DropDownList1.Items.Add(dv.Item(i).Row("photo_species"))

Answer 2

It is not clear if this is a vb.net (NOT vb6), and it not clear if this is a web page (asp.net), or a desktop only program?

If this is asp.net (web based), then this should work:

First, the web markup is this:

        <h3>Select Hotel</h3>
        <asp:DropDownList ID="DropDownList1" runat="server"
            DataValueField="ID"
            DataTextField="HotelName" height="30px" Width="206px">
        </asp:DropDownList>

Like most drop downs, there are (can be) two columns.

The "hidden" value - in most cases the database PK row ID.

And then the display value. (hence in above Value field, and text field).

DataValueField = hidden column - value returned from drop down DataTextField = the display column from the data.table (to display).

our code to load is thus this:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If Not IsPostBack Then

        LoadData()

    End If

End Sub


Sub LoadData()

    Using conn As New OleDbConnection(My.Settings.AccessDB)

        Dim strSQL =
            "SELECT ID, Hotelname FROM tblhotelsA ORDER BY HotelName"

        Using cmdSQL As New OleDbCommand(strSQL, conn)

            conn.Open()
            Dim rstData As New DataTable
            rstData.Load(cmdSQL.ExecuteReader)
            DropDownList1.DataSource = rstData
            DropDownList1.DataBind()

            ' add default please select
            DropDownList1.Items.Insert(0, New ListItem("Please Select Hotel", ""))
        End Using
    End Using

End Sub

And we now get this:

And if in code we need to test/get/look at/grab the selected value?

Then use this code:

    Debug.Print("drop down pk (id) = " & DropDownList1.SelectedItem.Value)
    Debug.Print("drop down hotel text = " & DropDownList1.SelectedItem.Text)

The above allows you to get both columns (the hidden one), and the text/display one.

As a general rule, you can also use the.Text property of the drop down list to get the selected value.

So, this also gets the value.

Debug.Print("drop down value = " & DropDownList1.Text)

so, above will return the same as DropDownList1.SelectedItem.Value