如果下拉列表的选定值从代码后面更改，如何更新UpdatePanel？

Question

我的下拉列表相互关联，我正在使用更新面板和sqldatasource，我想在设置从后面的代码中选择下拉值时更新更新面板。

Protected Sub Admin_ManageUsers_UserListing_new_PreRenderComplete(sender As Object, e As System.EventArgs) Handles Me.PreRenderComplete
    If Not IsPostBack Then
        ddlStatus.SelectedValue = _Status

        If ddlClients.Items.FindByValue(_Client.ToString()) Is Nothing = False Then
            ddlClients.SelectedValue = _Client
            dsCountries.DataBind()
            upCountry.Update()
        End If
        If ddlCountries.Items.FindByValue(_Country.ToString()) Is Nothing = False Then
            ddlCountries.SelectedValue = _Country
            sdsStates.DataBind()
            upStates.Update()
            upStore.Update()
        End If

        If ddlStates.Items.FindByValue(_State.ToString()) Is Nothing = False Then
            ddlStates.SelectedValue = _State
            sdsStates.DataBind()
            upStore.Update()
        End If

        If ddlStore.Items.FindByValue(_Store.ToString()) Is Nothing = False Then
            ddlStore.SelectedValue = _Store
        End If

        If ddlRole.Items.FindByValue(_Role.ToString()) Is Nothing = False Then
            ddlRole.SelectedValue = _Role
        End If

    End If
End Sub

如果对问题有任何疑惑，请帮助我。请问。谢谢。