Populate DropdownList based upon other DropDownList VB - asp.net

Question

I have found a couple of examples on the internet to do this but really struggling to get it working in VB. (Tried a converter but had mixed results)
I need the selection options of a Dropdownlist to be populated based upon the differing values in the first dropdown list.
Can anyone help with a releativley simple example in VB? Not fussed if the values are "hard coded" in the script. Or a SQL bit that pulls the data from a table
Thanks in advance!

Answer 1

The way it is done is to populate second dropdown in SelectedIndexChanged event of the first dropdown
Example:
Protected Sub ddlCountry_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
Dim CountryID As Integer = Convert.ToInt32(ddlCountry.SelectedValue.ToString())
FillStates(CountryID)
End Sub
Private Sub FillStates(ByVal countryID As Integer)
Dim strConn As String = ConfigurationManager.ConnectionStrings("DatabaseConnectionString").ConnectionString
Dim con As New SqlConnection(strConn)
Dim cmd As New SqlCommand()
cmd.Connection = con
cmd.CommandType = CommandType.Text
cmd.CommandText = "Select StateID, State from State where CountryID =#CountryID"
cmd.Parameters.AddWithValue("#CountryID", countryID)
Dim objDs As New DataSet()
Dim dAdapter As New SqlDataAdapter()
dAdapter.SelectCommand = cmd
con.Open()
dAdapter.Fill(objDs)
con.Close()
If objDs.Tables(0).Rows.Count > 0 Then
ddlState.DataSource = objDs.Tables(0)
ddlState.DataTextField = "State"
ddlState.DataValueField = "StateID"
ddlState.DataBind()
ddlState.Items.Insert(0, "--Select--")
Else
lblMsg.Text = "No states found"
End If
End Sub
With html source as so:
<asp:DropDownList ID="ddlState" runat="server" AutoPostBack="True">
</asp:DropDownList>
<asp:DropDownList ID="ddlCountry" runat="server"
AutoPostBack="True" OnSelectedIndexChanged="ddlCountry_SelectedIndexChanged">
</asp:DropDownList>

Answer 2

You could accomplish this declaratively in the ASPX page like this:
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:myConnString %>" SelectCommand="SELECT id, name FROM planets"></asp:SqlDataSource>
<asp:DropDownList ID="ddlPlanets" AutoPostBack="true" DataTextField="name" DataValueField="id" DataSourceID="SqlDataSource1" runat="server" AppendDataBoundItems="true" />
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:myConnString %>" SelectCommand="SELECT planetid, name FROM moons" FilterExpression="planetid = '{0}'">
<FilterParameters>
<asp:ControlParameter Name="planetid" ControlID="ddlPlanets" PropertyName="SelectedValue" />
</FilterParameters>
</asp:SqlDataSource>
<asp:DropDownList ID="ddlMoons" DataTextField="name" DataValueField="planetid" DataSourceID="SqlDataSource2" runat="server" />

Answer 3

Your best option will be to capture the SelectedIndexChanged event on the first dropdownlist, examine what the current value of that dropdownlist is, and then use that to clear and then populate the items in the second dropdownlist. When you do so, remember to set the AutoPostBack property of the first DropDownList to "true".