listbox添加的问题？

有3个listbox  listbox1 listbox2 listbox3
listbox1是省的信息  listbox2是对应市的信息现在前面2个联动好用但是我想点button实现把listbox2的值添到listbox3 中加了如下代码不好用只添加第一个省的市的信息请高手指点下应该怎么做才实现选完省信息对应的市添到listbox3中呢
Private Sub btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn.Click
        Dim i As Integer
        For i = 0 To (Me.listbox2.Items.Count) - 1
            If Me.listbox2.Items(i).Selected = True Then

                If Me.Listbox3.Items.Contains(Me.listbox2.Items(i)) = False Then

                    Listbox3.Items.Add(Me.listbox2.Items(i))
                End If
            End If
        Next i
    End Sub --------------------编程问答-------------------- 循环倒着写看看

Private Sub btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn.Click
        Dim i As Integer
        For i = Me.listbox2.Items.Count - 1 To 0 Step -1
            If Me.listbox2.Items(i).Selected = True Then
                If Me.Listbox3.Items.Contains(Me.listbox2.Items(i)) = False Then
                    Listbox3.Items.Add(Me.listbox2.Items(i))
                End If
            End If
        Next i
End Sub --------------------编程问答-------------------- LS的不好用哦。为什么我选listbox1里的值点击button  listbox2都是默认显示listbox1是1的值？ --------------------编程问答-------------------- 你的联动有问题,发代码上来看. --------------------编程问答-------------------- 哦联动是着样的也是在网上找的
     '建立数据库连接
        Dim conn As SqlConnection = New SqlConnection(ConfigurationSettings.AppSettings("connectionString")) '如果设置了web.config,也可以从web.config中读取数据库连接字符串
        conn.Open()
        Dim cmd As SqlCommand = New SqlCommand
        cmd.Connection = conn

        '=====================================================================================
        '生成客户端脚本控制的联动菜单
        '查询Tb_Province表获得所有的省份
        Dim sqlstr As String = "SELECT zhuid, zhuname FROM zhulm order by zhuid"
        cmd.CommandText = sqlstr
        Dim sqlda As SqlDataAdapter = New SqlDataAdapter(cmd)
        '建立临时表存储省份数据
        Dim Province As DataTable = New DataTable
        sqlda.Fill(Province)
        'Response.Write("将省份数据绑定到DropDownList1控件")
        'Response.End()

        '将省份数据绑定到DropDownList1控件
        listbox1.DataSource = Province
        listbox1.DataValueField = "zhuid"
        listbox1.DataTextField = "zhuname"
        If Not IsPostBack Then listbox1.DataBind()

        '获取省份的个数
        Dim ProvinceNum As Integer = Province.Rows.Count()

        '使用StringBuilder构造含客户端控制脚本的字符串
        Dim sbscript As New System.Text.StringBuilder
        sbscript.Append("<script>")
        sbscript.Append("<")
        sbscript.Append("/")
        sbscript.Append("script>")

        '注册客户端脚本，将脚本内容写入客户端输出流
        Dim strscript As String = sbscript.ToString()

        If (Not IsClientScriptBlockRegistered("clientScript")) Then
            RegisterClientScriptBlock("clientScript", strscript)
        End If
        '=====================================================================================

        '初始化DropDownList2中的内容
        sqlstr = "SELECT fuid,funame FROM fulm WHERE (Left(zhuid,2) = '" & Province.Rows(0)(0) & "')"
        cmd.CommandText = sqlstr
        sqlda = New SqlDataAdapter(cmd)

        Dim dtCity As DataTable = New DataTable
        sqlda.Fill(dtCity)

        listbox2.DataSource = dtCity
        listbox2.DataValueField = "fuid"
        listbox2.DataTextField = "funame"
        If Not IsPostBack Then listbox2.DataBind()

        sqlda.Dispose()
        cmd.Dispose()
        conn.Close() --------------------编程问答-------------------- 你是用的客户端的连动,不能保存listbox2的状态.
所以出现这种情况,简单的做法是在服务器端连动,
将 listbox1的autopostback设为true,在selectedindexchanged事件中联动,这样才能保存状态,

否则用上面的方法还要在Page_load中重新根据listbox1的选项再生成listbox2的选项,然后根据Request.Form["listobx2的值来设置listbox2的选中的项. --------------------编程问答-------------------- 直接绑定的话
把值取出来然后赋值给list3 --------------------编程问答-------------------- selectedindexchanged 是什么事件没用过 --------------------编程问答-------------------- 大哥们详细给讲讲把不会写 --------------------编程问答-------------------- selectedindexchanged 就是选择listbox1时触发的服务器事件，将litbox1设成autopostback="true"
就会触发这个事件。

--------------------编程问答-------------------- HTML代码：
<asp:Listbox ID="Listbox1" runat="server" OnSelectedIndexChanged="Listbox 1_SelectedIndexChanged" AutoPostBack="True">
CS代码：
protected void Listbox1_SelectedIndexChanged(object sender, EventArgs e)
{
     这里根据listbox1的selectedvalue来绑定listbox2
}
--------------------编程问答--------------------

引用 10 楼 cpp2017 的回复:

HTML代码：
<asp:Listbox ID="Listbox1" runat="server" OnSelectedIndexChanged="Listbox 1_SelectedIndexChanged" AutoPostBack="True">
CS代码：
protected void Listbox1_SelectedIndexChanged(object sender, EventArgs e)
{
这里根据listbox1的selectedvalue来绑定listbox2
}

要是着样联动的话就不用我上面的代码了把？怎么联动。。。 --------------------编程问答-------------------- 不用上面的代码了。怎么联动？

查数据库，绑定listbox2
条件就是省=listbox1的选中的值，这里应该是单选吧？考虑用dropdownlsit --------------------编程问答-------------------- 不知道要怎么写 --------------------编程问答-------------------- 谁会给个例子什么的可以么不知道应该怎么做 --------------------编程问答-------------------- 好久了大家帮帮忙把

补充：.NET技术 ,  ASP.NET