Html select 不填充其他控件的下拉列表

我是一个完全的网络应用新手，但现在开始了

我有一个带有下拉列表的web表单，它通过数据库过程填充度假胜地列表。那个钻头很好用。当我从列表中选择一个项目时，我需要在列表框中填充该度假村特定的酒店

这一点我遇到了麻烦，如果我从下拉列表中单击表单上的日历控件，列表就会填充

问题：在我从下拉列表中点击值后，如何让它填充列表

谢谢

顺便说一下，下面是代码：

Private Sub Page_Init(sender As Object, e As System.EventArgs) Handles Me.Init
    Me.Calendar1.SelectedDate = Now()


    Me.DropDownList1.Items.Clear()

    Dim connStr As String = Web.Configuration.WebConfigurationManager.ConnectionStrings("ITC").ConnectionString
    Dim conn As New SqlClient.SqlConnection(connStr)
    conn.Open()

    Dim sqlProducts As String = "<<sql_string>>"

    Dim da As New SqlDataAdapter(sqlProducts, conn)
    Dim ds As New DataSet()
    da.Fill(ds, "Products")

    DropDownList1.DataTextField = "Rcode"
    DropDownList1.DataValueField = "Rcode"
    DropDownList1.DataSource = ds.Tables("Products")
    DropDownList1.DataBind()

    ds.Dispose()
    da.Dispose()

    conn.Close()

End Sub

Protected Sub DropDownList1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownList1.SelectedIndexChanged

    Me.ListBox1.Items.Clear()
    Me.ListBox2.Items.Clear()

    Dim connStr As String = WebConfigurationManager.ConnectionStrings("ITC").ConnectionString
    Dim conn As New SqlConnection(connStr)
    conn.Open()

    Dim sqlProducts As String = "sql_string '" & Me.DropDownList1.Text & "'"

    Dim da As New SqlDataAdapter(sqlProducts, conn)
    Dim ds As New DataSet()
    da.Fill(ds, "Products")

    ListBox1.DataTextField = "accommDescription"
    ListBox1.DataValueField = "accommCode"
    ListBox1.DataSource = ds.Tables("Products")
    ListBox1.DataBind()

    ds.Dispose()
    da.Dispose()
    conn.Close()

    ListBox1.Focus()

End Sub