In the. NET Framework, a file type is generally used to process files (. ashx ). It can be used as a server in Ajax development. In particular, when a request stays on a page, the following example is used to implement cascading update in the HTML drop-down list.
(1) ddlinnerjoin. aspx code:
<% @ Page Language = "C #" autoeventwireup = "true" codefile = "ddlinnerjoin. aspx. cs" inherits = "ddlinnerjoin" %>
<! Doctype HTML public "-// W3C // dtd xhtml 1.0 transitional // en" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<HTML xmlns = "http://www.w3.org/1999/xhtml">
<Head runat = "server">
<Title> No title page </title>
<SCRIPT type = "text/JavaScript" src = "ddlinnerjoin. js"> </SCRIPT>
</Head>
<Body>
<Form ID = "form1" runat = "server">
<Div>
<Select id = "Major" onchange = "startrequest ();">
<Option value = "1"> Software Technology </option>
<Option value = "2"> network technology </option>
</SELECT>
<Select id = "class">
</SELECT>
</Div>
</Form>
</Body>
</Html>
(2) ddlinnerjoin. js code:
/* Creator: haohai
Created on: 2007-6-4
Version: 1.0
*/
VaR XMLHTTP;
VaR requesttype = "";
Function createxmlhttp ()
{
If (window. XMLHttpRequest)
{
XMLHTTP = new XMLHttpRequest (); // Mozilla Browser
}
Else if (window. activexobject)
{
Try
{
XMLHTTP = new activexobject ("msxml2.xmlhttp"); // old version of IE
}
Catch (E)
{
}
Try
{
XMLHTTP = new activexobject ("Microsoft. XMLHTTP"); // new version of IE
}
Catch (E)
{
}
If (! XMLHTTP)
{
Window. Alert ("the XMLHTTPRequest object cannot be created! ");
Return false;
}
}
}
Function startrequest ()
{
Createxmlhttp ();
// Use the get Method
VaR url = "ddlinnerjoin. ashx? Major = "+ document. getelementbyid (" Major "). Options. value;
XMLHTTP. Open ("get", URL, true );
XMLHTTP. onreadystatechange = bindclass;
XMLHTTP. Send (null );
}
Function bindclass ()
{
If (XMLHTTP. readystate = 4)
{
If (XMLHTTP. Status = 200)
{
VaR selclass = Document. getelementbyid ("class ");
// If the passive (triggered) drop-down has content, clear the content first.
While (selclass. haschildnodes ())
{
VaR node = selclass. Children (0)
Selclass. removechild (node );
}
// Obtain the response content
VaR result = XMLHTTP. responsetext;
// Split to facilitate binding
VaR optiontext = result. Split ('');
// Bind the split content to the passive drop-down list
For (VAR I = 0; I <optiontext. length; I ++)
{
VaR optionnode = Document. createelement ("option ");
Optionnode. Text = optiontext [I];
Selclass. Add (optionnode );
}
}
}
}
(3) ddlinnerjoin. ashx code:
<% @ Webhandler Language = "C #" class = "ddlinnerjoin" %>
// Creator: haohai
// Creation date: 2007-6-4
// Version 1.0
Using system;
Using system. Web;
// Introduce the namespace to access the database
Using system. Data. sqlclient;
Using system. Data;
Public class ddlinnerjoin: ihttphandler {
Public void processrequest (httpcontext context ){
Context. response. contenttype = "text/plain ";
String majorid = context. Request. Params ["Major"]. tostring (). Trim ();
String major = "";
// Avoid not recognizing Chinese Characters
If (majorid = "1 ")
{
Major = "software technology ";
}
Else if (majorid = "2 ")
{
Major = "Network Technology ";
}
// Extract data from the database
Sqlconnection conn = new sqlconnection ("Server =.; database = tuition; uid = sa; Pwd = sa ;");
Sqldataadapter da = new sqldataadapter ("select classname from dictblclass where classname like '" + major + "%'", Conn );
Dataset DS = new dataset ();
Da. Fill (DS );
// Define the response text format to return
String result = "";
Foreach (datarow row in DS. Tables [0]. Rows)
{
Result + = row [0]. tostring (). Trim () + "";
}
Context. response. Write (result. Trim ());
// Context. response. Write ("Hello World ");
}
Public bool isreusable {
Get {
Return false;
}
}
}
In this way, you can easily implement cascade updates, especially when the data volume is large.
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