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标题: Ajax基础-XMLHttpRequest对象的创建、数据请求和处理 [打印本页]

作者: tznktg 时间: 2007-9-19 23:01
标题: Ajax基础-XMLHttpRequest对象的创建、数据请求和处理
XMLHttpRequest是Ajax的基础对象。异步的数据请求是通过这个对象来实现的。下面的代码是建立XMLHttpRequest对象的示例。

代码在IE6、FireFox1.5、NetScape8.1、Opera8.54调试通过。服务器为Window2000 + IIS5

1、创建XMLHTTPREQUEST对象

var xhr;
var requestType = "";

//xhr = new XMLHttpRequest();

function createXMLHttpRequest()
{
if (window.ActiveXObject) // IE下创建XMLHTTPREQUEST
{
      xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
else if (window.XMLHttpRequest) // 其他浏览器创建XMLHTTPREQUEST
{
      xhr = new XMLHttpRequest();
}
}

这种方法对于低版本的IE不适合。

2、XMLHTTPREQUEST对象请求数据

function startRequest(requestedList)
{
if (xhr)
{
      requestType = requestedList;
      createXMLHttpRequest();
      xhr.onreadystatechange = handleStateChange;
      xhr.open("GET","../ajax/paraseXML.xml",true);
      xhr.send(null);
}
else
      alert("XMLHTTPREQUEST IS FALSE");
}

这是个处理XML文档的示例，请求的文件是paraseXML.xml文件
这里需要说明的是：如果请求的是一个HTML文件，服务器对象会将所有的标签全部返回，包括<HTML>、<head>、<meta>等标签。响应数据如果包含HTML标签，最好把这些标签去掉。

3、XMLHTTPREQUEST对象返回数据处理

function handleStateChange()
{
if (xhr.readyState == 4)
{
      if (xhr.status == 200)
      {
         if (requestType == "north")
         {
            listNorthStates();
         }
         if (requestType == "all")
         {
            listAllStates();
         }
      }
}
}

4、数据处理函数

function listNorthStates()
{
// xhr 为XMLHTTPREQUEST对象
// xmlDoc为XMLHTTPREQUEST响应的XML文档对象
var xmlDoc = xhr.responseXML; // 取得XML文档对象
var northNode = xmlDoc.getElementsByTagName("north")[0]; // 取得所有处于北方的节点
var northStates = northNode.getElementsByTagName("state"); // 在处于北方的节点中提取省份数据
outputList("north States", northStates); // 输出省份数据
}

function listAllStates()
{
var xmlDoc = xhr.responseXML;
var allStates = xmlDoc.getElementsByTagName("state"); // 取得所有的省份数据
outputList("All States in document ",allStates); // 输出省份的数据
}
/**********************************************************
// 输出数据
// title: 输出数据的标题
// states: 输出数据来源
********************************************************/
function outputList(title,states)
{
var out = title;
var currentState = null; // 初始化省份对象
for (var i = 0; i < states.length; i++) // 列出Ststes对象的所有数据,生成输出串
{
      currentState = states; // 取得当前的省份
      // 生成输出HTML字符串
      out = out + "<ul><font face='仿宋_GB2312'><span style='font-size: 9pt'>";
      out = out + "<li>" + currentState.childNodes[0].nodeValue + "</li>";
      out = out + "</span></font></ul>";
}
// 取得输出串的对象,输出生成的字符串
var test = document.getElementById("test");
test.innerHTML = out;
}

5、完整示例文件

<!DOCTYPE html PUBLIC "-//W3C//DTD XHML 1.0 Strict//EN" "http://www.w3.org/TR/xHML/DTD/xhtml-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
<meta http-equiv="Content-Type" CONTENT="text/html; charset=gb2312">
<meta http-equiv="Cache-Control" CONTENT="no-cache">
<meta http-equiv="Pragma" CONTENT="no-cache">
<meta http-equiv="Expires" CONTENT="0">

<title>AJAX 测试</title>
<script type="text/javascript">
///// 创建XMLHttpRequest对象
var xhr;
var requestType = "";

//xhr = new XMLHttpRequest();

function createXMLHttpRequest()
{
if (window.ActiveXObject)
{
      xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
else if (window.XMLHttpRequest)
{
      xhr = new XMLHttpRequest();
}
}
///// ＸＭＬ文档处理
function startRequest(requestedList)
{
if (xhr)
{
      requestType = requestedList;
      createXMLHttpRequest();
      xhr.onreadystatechange = handleStateChange;
      xhr.open("GET","../ajax/paraseXML.xml",true);
      xhr.send(null);
}
else
      alert("XMLHTTPREQUEST IS FALSE");
}

function handleStateChange()
{
if (xhr.readyState == 4)
{
      if (xhr.status == 200)
      {
         if (requestType == "north")
         {
            listNorthStates();
         }
         if (requestType == "all")
         {
            listAllStates();
         }
      }
}
}

function listNorthStates()
{
var xmlDoc = xhr.responseXML;
var northNode = xmlDoc.getElementsByTagName("north")[0];
var northStates = northNode.getElementsByTagName("state");
outputList("north States", northStates);
}
function listAllStates()
{
var xmlDoc = xhr.responseXML;
var allStates = xmlDoc.getElementsByTagName("state");
outputList("All States in document ",allStates);
}
function outputList(title,states)
{
var out = title;
var currentState = null;
for (var i = 0; i < states.length; i++)
{
      currentState = states;
      out = out + "<ul><font face='仿宋_GB2312'><span style='font-size: 9pt'>";
      out = out + "<li>" + currentState.childNodes[0].nodeValue + "</li>";
      out = out + "</span></font></ul>";
}
var test = document.getElementById("test");
test.innerHTML = out;
}
</script>

</head>

<body>

<form action="#">

<input type=“button" value="AJAX Test north" onclick="startRequest('north');"/>
<input type="button" value="AJAX Test all" onclick="startRequest('all');"/>

<input type="button" value="AJAX Test ASPX" onclick="startRequestFromServer();"/>

<input type="button" value="search" onclick="startRequestFromLanguage()"/>
</form>

<div id="test"><font face="仿宋_GB2312"><span style="font-size: 9pt"></span></font>
</div>
</body>

</html>

6、参考书籍

《Ajax基础教程》人民邮电出版社

本程序为该书的一些示例，仅供入门参考

7、补充

忘记XML文件: paraseXml.xml
将该文件与上面的HTML文件放在相同的目录下即可

<?xml version="1.0" encoding="UTF-8"?>
<states>
<north>
      <state>辽宁</state>
      <state>吉林</state>
      <state>黑龙江</state>
      <state>内蒙古</state>
</north>
<south>
      <state>福建</state>
      <state>广东</state>
      <state>云南</state>
      <state>广西</state>
</south>
<east>
      <state>上海</state>
      <state>浙江</state>
      <state>江苏</state>
      <state>安徽</state>
</east>
<west>
      <state>新疆</state>
      <state>陕西</state>
      <state>山西</state>
      <state>宁夏</state>
</west>
</states>

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