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Ajax & XMLHttpRequset

 1<%@ Page language="c#" Codebehind="$FILENAME$.cs" AutoEventWireup="false" Inherits="$INHERITS$" %>
 2<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
 3
 4<html>
 5  <head>
 6    <title>Ajax_exam1</title>
 7    <meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
 8    <meta name="CODE_LANGUAGE" Content="C#">
 9    <meta name=vs_defaultClientScript content="JavaScript">
10    <meta name=vs_targetSchema content="">
11    <meta http-equiv="Content-Type" content="text/html charset=big5 "/>
12    <script language=javascript>
13   
14        var ajax;
15        function CreateAJAX()
16        {
17            if(window.ActiveXObject)
18            {
19                try
20                {
21                    return new ActiveXObject("Msxml2.XMLHTTP");
22                }
23                catch(e)
24                {
25                    try
26                    {
27                        return new ActiveXObject("Microsoft.XMLHTTP");
28                    }
29                    catch(e2)
30                    {
31                        return null;
32                    }
33                }
34            }
35            else if(window.XMLHttpRequest)
36            {
37                return new XMLHttpRequest();
38            }
39            else
40            {
41                return null;
42            }
43        }
44       
45        function onRcvData()
46        {
47            if(ajax.readyState == 4)
48            {
49                if(ajax.status == 200)
50                {
51                    var content = document.getElementById('content');
52                    content.innerHTML = ajax.responseText;
53                }
54                else
55                {
56                    alert('Error from server !');
57                }
58            }
59        }
60       
61        function ajaxSendRequest(url)
62        {
63            ajax = CreateAJAX();
64            if(!ajax)
65            {
66                alert('explorer is unsupport !');
67                return 0;
68            }
69       
70            ajax.onreadystatechange = onRcvData;
71            ajax.open("GET",url,true);
72            ajax.send("");
73        }
74       
75       
76    </script>
77  </head>
78  <body MS_POSITIONING="GridLayout">
79   
80    <div id="content"></div>
81    <br>
82    <input type="button" value="search" onclick="ajaxSendRequest('http://www.baidu.com')">
83   
84  </body>
85</html>
86
  請看上面一個簡單的例子,通過他,我們能夠初步認識Ajax架構的工作模式!本例子,只包含了一個DIV標籤,用來顯示最後的結果,以及一個”查詢”button.整個執行流程如下:

Ajax的精神在於非同步傳輸,所以,在Ajax發出清球后,並不會待server的回應,而必須指定一個特定的對象讓XMLHttpRequest在接收到server的回應的時候通知javascript.這個負責通知的onreadystatechange.

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