对asp.net实现DropDownList、ListBox无刷新三级联动(javascript)的改进

上篇文章说明了如何实现三级联动，但如果数据量较大，加载时会慢一些，因此经过测试，将需要读取的数据先写入一个文本文件中，然后在加载页面时直接调用此文本文件的内容，省去了读取数据库浪费的时间，数据量大时速度比先前快了许多。

数据库请见上一篇文章“asp.net实现DropDownList、ListBox无刷新三级联动(javascript)”

生成数据文本文件的代码

//将地区信息写入文本文件area.js

//添加二级地区

string strAreaData, strSQL;

strAreaData = "<script language = 'JavaScript' type='text/javascript'>var onecount;onecount=0;subcat = new Array();";

strSQL = "select * from nts_area where oneid<>0 and twoid<>0 and threeid=0 order by sort";

IDataReader dr = DataClass.GetDataReader(strSQL);

int i1 = 0;

while (dr.Read())

strAreaData += "onecount=" + i1.ToString() + ";";

//添加三级地区

strAreaData += "var onecount1;onecount1=0;subcat1 = new Array();";

strSQL = "select * from nts_area where oneid<>0 and twoid<>0 and threeid<>0 order by sort";

dr = DataClass.GetDataReader(strSQL);

int n1 = 0;

while (dr.Read())

dr.Close();

strAreaData += "onecount1=" + n1.ToString() + ";</script>";

StreamWriter str;

File.Delete(Server.MapPath("~/js/area.js"));

str = File.CreateText(Server.MapPath("~/js/area.js"));

str.WriteLine(strAreaData);

str.Close();

aspx页面代码
<%--地区无刷新显示 --%>

<% Response.WriteFile(Server.MapPath("~/js/area.js")); %>

<script language = "JavaScript" type="text/javascript">

function changearea1()

function changearea2()

</script>

<asp:DropDownList ID="Ddl_AreaOne" runat="server" AppendDataBoundItems="True">

<asp:ListItem Value="0">请选择</asp:ListItem>

</asp:DropDownList>

<asp:DropDownList ID="Ddl_AreaTwo" runat="server" >

<asp:ListItem Value="0">请选择</asp:ListItem>

</asp:DropDownList>

<asp:DropDownList ID="Ddl_AreaThree" runat="server" >

<asp:ListItem Value="0">请选择</asp:ListItem>

</asp:DropDownList>

cs页面代码

protected void Page_Load(object sender, EventArgs e)

{

Ddl_AreaOne.Attributes.Add("onchange", "changearea1()");

Ddl_AreaTwo.Attributes.Add("onchange", "changearea2()");

string strSQL;

strSQL = "select * from nts_area where oneid<>0 and twoid=0 and threeid=0 order by sort";

Ddl_AreaOne.DataSource = DataClass.GetDataReader(strSQL); //此为我写的读取DataReader对象的类

Ddl_AreaOne.DataTextField = "areaname";

Ddl_AreaOne.DataValueField = "oneid";

Ddl_AreaOne.DataBind();

}