/**
 * Ajax 类
 *   sUrl : 目标 URL
 *   sQueryString : 提交变量
 *   callbackFunc : 回调函数
 *   callbackParams : 回调函数参数
 *   sRecvType : 返回值格式 ( 0: 文本, 1: XML );
 */

function Ajax ( sUrl, sQueryString, callbackFunc, callbackParams, sRecvType )
{
    this.url = sUrl;
    this.queryString = sQueryString != null ? sQueryString : '';
    this.response; // 返回值
    this.maxRetry = 3; // 最大重试次数
    this.countRetry = 0; // 重试次数

    this.xmlHttp = this.createXMLHttpRequest ();
    if ( this.xmlHttp == null )
    {
        return false;
    }
    var objxml = this.xmlHttp;
    objxml.onreadystatechange = function ()
    {
        try
        {
            Ajax.handleStateChange ( objxml, sRecvType, callbackFunc, callbackParams )
        }
        catch ( e ) {}        
    }
}

Ajax.prototype.createXMLHttpRequest = function ()
{
	try
	{
		return new XMLHttpRequest ();
	}
	catch(e)
	{
	    try
	    {
	    	return new ActiveXObject ( 'Msxml2.XMLHTTP' );
	    }
	    catch(e)
	    {
	    	try
		    {
				return new ActiveXObject ( 'Microsoft.XMLHTTP' );
		    }
		    catch(e)
		    {
		    }
	    }
	}
    
    return null;
}

Ajax.prototype.createQueryString = function ()
{
    var queryString = '';
    if ( this.queryString != null && typeof ( this.queryString ) != 'string' )
    {
        var elements = this.queryString.elements;
        var pairs = new Array();
        for(var i=0;i<elements.length;i++){
            if((name=elements.name)&&(value = elements.value)){
                var eType = elements.getAttribute('type');
                if ( ( eType != 'radio' && eType != 'checkbox' ) || elements.checked )
                {
                    pairs.push(name + "=" + encodeURIComponent(value));
                }
            }
        }
        queryString = pairs.join ( '&' );
    }
    else
    {
        queryString = this.queryString;
    }
    return queryString;
}

Ajax.prototype.get = function ()
{
    sUrl = this.url;

    var queryString = sUrl;
    if ( extraQueryString = this.createQueryString() )
    {
        queryString += ( queryString.indexOf ('?') > 0 ? '&' : '?' ) + extraQueryString;
    }
    this.xmlHttp.open ( 'GET', queryString, true );
    this.xmlHttp.send ( null );
}

Ajax.prototype.post = function ()
{
    var sUrl = this.url;
    var queryString = this.createQueryString ();
    this.xmlHttp.open ( 'POST', sUrl, true );
    this.xmlHttp.setRequestHeader ( 'Content-Type', 'application/x-www-form-urlencoded' );
    this.xmlHttp.send ( queryString );
}

Ajax.handleStateChange = function ( xmlHttp, sRecvType, callbackFunc, callbackParams )
{
    if ( xmlHttp.readyState == 4 )
    {
        if ( xmlHttp.status == 200  )
        {
            Response = sRecvType ? xmlHttp.responseXML : xmlHttp.responseText;
            if ( callbackFunc != null )
            {
                callbackFunc ( Response, callbackParams );
                return true;
            }
            else
            {
            	document.getElementById(callbackParams).innerHTML=Response;
            }
        }
    }
}