/*******************************
  AJAX相關基礎，希望對大家都有幫助

  [open]方法中包含了5個參數，前三個是必要的，后兩個是可選的(在服務器需要進行身份驗證時提供)，參數如下：
  http-method：HTTP的通信方式，比如GET或是POST
  url：接收XML數據的服務器的URL地址。通常在URL中要指明 ASP或CGI程序
  async：一個布爾標識，說明請求是否為異步的。如果是異步通信方式(true)，客戶機就不等待服務器的響應；如果是同步方式(false)，客戶機就要等到服務器返回消息后才去執行其他操作
  userID: 用戶ID，用于服務器身份驗證
  password: 用戶密碼，用于服務器身份驗證

  xmlObj.[setRequestHeader]('CONTENT-TYPE','application/x-www-form-urlencoded');
  //設置content type，作為表單數據發送

  [send]方法的參數類型可以是字符串、DOM樹或任意數據流

  在客戶端發送數據的過程中，與服務器端的交互狀態是不斷的發生變化的
[0]uninitialized未初始化(在XMLHttpRequest開始前)(還沒開始)
[1]loading(一旦初始化)(加載中)
[2]loaded(一旦XMLHttpRequest從服務器端獲得響應)(已加載)
[3]interactive(當對象連接到服務器)(信息交互中)
[4]complete(完成)(完成)

  var returnText = xmlObj.responseText;  //傳回的值作為字符串來處理
  var returnStream = xmlObj.responseStream;   //傳回的值作為Stream
  var returnXml = xmlObj.responseXML;  //傳回的值作為XMLDocument對象來處理，可以通過 JavaScript DOM 的相關函數處理
*******************************/

function createRequest()
{
  var http_request;

  if(window.XMLHttpRequest) { 
    http_request = new XMLHttpRequest();
    if (http_request.overrideMimeType) {
      http_request.overrideMimeType("text/xml");
    }
  }
  else if (window.ActiveXObject) { 
    try {
      http_request = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (e) {
      try {
        http_request = new ActiveXObject("Microsoft.XMLHTTP");
      } catch (e) {}
    }
  }
  if (!http_request) { 
    window.alert("can't create XMLHttpRequest object.");
    return null;
  }  
  return http_request;
}

var net = new Object();
net.READY_STATE_UNINITIALIZED = 0;
net.READY_STATE_LOADING       = 1;
net.READY_STATE_LOADED        = 2;
net.READY_STATE_INTERACTIVE   = 3;
net.READY_STATE_COMPLETE      = 4;
net.ContentLoader = function (url, onload, onerror, method, params, contentType)
{
  this.url = url;
  this.req = null;
  this.onload = onload;
  this.onerror = (onerror) ? onerror : this.defaultError;
  this.loadXMLDoc(url, method, params, contentType);
}
net.ContentLoader.prototype = {
  loadXMLDoc : function(url, method, params, contentType)
  {
    if (!method)
      method = 'GET';
    if (!contentType && method=='POST')
      contentType = 'application/x-www-form-urlencoded';
    this.req = createRequest();
    //if (window.ActiveXObject)
    //  this.req = new ActiveXObject("Microsoft.XMLHTTP");
    //else if (window.XMLHttpRequest)
    //  this.req = new XMLHttpRequest();
    if (this.req)
    {
      try
      {
        var loader = this;
        this.req.onreadystatechange = function()
        {
          loader.onReadyState.call(loader);
        }
        this.req.open(method, url, true);
        if (contentType)
          this.req.setRequestHeader('Content-Type', contentType);
        this.req.send(params);
      }
      catch(err)
      {
        this.onerror.call(this);
      }
    }
  },
  onReadyState : function()
  {
    var req = this.req;
    var ready = req.readyState;
    if (ready==net.READY_STATE_COMPLETE)
    {
      var httpStatus = req.status;
      if (httpStatus==200 || httpStatus==0)
        this.onload.call(this);
      else
        this.onerror.call(this);
    }
  },
  defaultError : function()
  {
    return;
    alert('error fetching data!' +
      '\n\nreadyState:' + this.req.readyState +
      '\nstatus:' + this.req.status +
      '\nheaders:'+ this.req.getAllResponseHeaders());
  }
}

function LoadXML(doc)
{
  var Browser = new Object();
  Browser.isMozilla = (typeof document.implementation != 'undefined') && (typeof document.implementation.createDocument != 'undefined') && (typeof HTMLDocument!='undefined');
  Browser.isIE = window.ActiveXObject ? true : false;
  Browser.isFirefox = (navigator.userAgent.toLowerCase().indexOf('firefox')!=-1);
  Browser.isOpera = (navigator.userAgent.toLowerCase().indexOf('opera')!=-1);
  var xml;
  if (Browser.isFirefox)
  {
    xml = new DOMParser().parseFromString(doc, "text/xml");
  }
  else
  {
    xml = new ActiveXObject("MSXml.DOMDocument");
    xml.loadXML(doc);
  }
  return xml;
}