关于ajax上传文件的流程 和选择图片立即显示

关键点:

1.制作一个表单..然后把上传字段附加到该表单中

2.制作一个框架..把表单的_target的属性指向该框架.

3.提交表单..

jQuery.extend({

    createUploadIframe: function(id, uri)
    {
            //create frame
            var frameId = 'jUploadFrame' + id;
            var iframeHtml = '<iframe id="' + frameId + '" name="' + frameId + '" style="position:absolute; top:-9999px; left:-9999px"';
            if(window.ActiveXObject)
            {
                if(typeof uri== 'boolean'){
                    iframeHtml += ' src="' + 'javascript:false' + '"';

                }
                else if(typeof uri== 'string'){
                    iframeHtml += ' src="' + uri + '"';

                }
            }
            iframeHtml += ' />';
            jQuery(iframeHtml).appendTo(document.body);

            return jQuery('#' + frameId).get();
    },
    createUploadForm: function(id, fileElementId, data)
    {
        //create form
        var formId = 'jUploadForm' + id;
        var fileId = 'jUploadFile' + id;
        var form = jQuery('<form  action="" method="POST" name="' + formId + '" id="' + formId + '" enctype="multipart/form-data"></form>');
        if(data)
        {
            for(var i in data)
            {
                jQuery('<input type="hidden" name="' + i + '" value="' + data[i] + '" />').appendTo(form);
            }
        }
        var oldElement = jQuery('#' + fileElementId);
        var newElement = jQuery(oldElement).clone();
        jQuery(oldElement).attr('id', fileId);
        jQuery(oldElement).before(newElement);
        jQuery(oldElement).appendTo(form);

        //set attributes
        jQuery(form).css('position', 'absolute');
        jQuery(form).css('top', '-1200px');
        jQuery(form).css('left', '-1200px');
        jQuery(form).appendTo('body');
        return form;
    },

    ajaxFileUpload: function(s) {
        // TODO introduce global settings, allowing the client to modify them for all requests, not only timeout
        s = jQuery.extend({}, jQuery.ajaxSettings, s);
        var id = new Date().getTime()
        var form = jQuery.createUploadForm(id, s.fileElementId, (typeof(s.data)=='undefined'?false:s.data));
        var io = jQuery.createUploadIframe(id, s.secureuri);
        var frameId = 'jUploadFrame' + id;
        var formId = 'jUploadForm' + id;
        // Watch for a new set of requests
        if ( s.global && ! jQuery.active++ )
        {
            jQuery.event.trigger( "ajaxStart" );
        }
        var requestDone = false;
        // Create the request object
        var xml = {}
        if ( s.global )
            jQuery.event.trigger("ajaxSend", [xml, s]);
        // Wait for a response to come back
        var uploadCallback = function(isTimeout)
        {
            var io = document.getElementById(frameId);
            try
            {
                if(io.contentWindow)
                {
                     xml.responseText = io.contentWindow.document.body?io.contentWindow.document.body.innerHTML:null;
                     xml.responseXML = io.contentWindow.document.XMLDocument?io.contentWindow.document.XMLDocument:io.contentWindow.document;

                }else if(io.contentDocument)
                {
                     xml.responseText = io.contentDocument.document.body?io.contentDocument.document.body.innerHTML:null;
                    xml.responseXML = io.contentDocument.document.XMLDocument?io.contentDocument.document.XMLDocument:io.contentDocument.document;
                }
            }catch(e)
            {
                jQuery.handleError(s, xml, null, e);
            }
            if ( xml || isTimeout == "timeout")
            {
                requestDone = true;
                var status;
                try {
                    status = isTimeout != "timeout" ? "success" : "error";
                    // Make sure that the request was successful or notmodified
                    if ( status != "error" )
                    {
                        // process the data (runs the xml through httpData regardless of callback)
                        var data = jQuery.uploadHttpData( xml, s.dataType );
                        // If a local callback was specified, fire it and pass it the data
                        if ( s.success )
                            s.success( data, status );

                        // Fire the global callback
                        if( s.global )
                            jQuery.event.trigger( "ajaxSuccess", [xml, s] );
                    } else
                        jQuery.handleError(s, xml, status);
                } catch(e)
                {
                    status = "error";
                    jQuery.handleError(s, xml, status, e);
                }

                // The request was completed
                if( s.global )
                    jQuery.event.trigger( "ajaxComplete", [xml, s] );

                // Handle the global AJAX counter
                if ( s.global && ! --jQuery.active )
                    jQuery.event.trigger( "ajaxStop" );

                // Process result
                if ( s.complete )
                    s.complete(xml, status);

                jQuery(io).unbind()

                setTimeout(function()
                                    {    try
                                        {
                                            jQuery(io).remove();
                                            jQuery(form).remove();    

                                        } catch(e)
                                        {
                                            jQuery.handleError(s, xml, null, e);
                                        }                                    

                                    }, )

                xml = null

            }
        }
        // Timeout checker
        if ( s.timeout >  )
        {
            setTimeout(function(){
                // Check to see if the request is still happening
                if( !requestDone ) uploadCallback( "timeout" );
            }, s.timeout);
        }
        try
        {

            var form = jQuery('#' + formId);
            jQuery(form).attr('action', s.url);
            jQuery(form).attr('method', 'POST');
            jQuery(form).attr('target', frameId);
            if(form.encoding)
            {
                jQuery(form).attr('encoding', 'multipart/form-data');
            }
            else
            {
                jQuery(form).attr('enctype', 'multipart/form-data');
            }
            jQuery(form).submit();

        } catch(e)
        {
            jQuery.handleError(s, xml, null, e);
        }

        jQuery('#' + frameId).load(uploadCallback    );
        return {abort: function () {}};    

    },

    uploadHttpData: function( r, type ) {
        var data = !type;
        data = type == "xml" || data ? r.responseXML : r.responseText;
        // If the type is "script", eval it in global context
        if ( type == "script" )
            jQuery.globalEval( data );
        // Get the JavaScript object, if JSON is used.
        if ( type == "json" )
            eval( "data = " + data );
        // evaluate scripts within html
        if ( type == "html" )
            jQuery("<div>").html(data).evalScripts();

        return data;
    }
})

很多人问：在上传图片文件时，在上传之前怎么进行无刷新预览呢？这里我把我所使用的方法写一下，包括了flash和视频文件，代码如下。

选择页面JS代码：
<script language="javascript">
function checkData()
{
   var fileName=document.getElementById("FileUp").value;
   if(fileName=="")
     return;
     //检查文件类型
   var exName=fileName.substr(fileName.lastIndexOf(".")+1).toUpperCase()
      if(exName=="JPG"||exName=="BMP"||exName=="GIF")
       {
          //document.getElementById("myimg").src=fileName;
          document.getElementById("previewImage").innerHTML='<img src=\''+fileName+'\' width=100 height=100 >';
       }
     else
       if(exName=="SWF")
        {
          document.getElementById("previewImage").innerHTML='<embed src=\''+fileName+'\' width=\'100\' height=\'100\' quality=\'high\' bgcolor=\'#f5f5f5\' ></embed>';
         }
     else
        if(exName=="WMV"||exName=="MPEG"||exName=="ASF"||exName=="AVI")
         {
            var strcode='<embed src=\''+fileName+'\' border=\'0\' width=\'100\' height=\'100\'  quality=\'high\' ';
            strcode+=' autoStart=\'1\' playCount=\'0\' enableContextMenu=\'0\' type=\'application/x-mplayer2\'></embed>';
            document.getElementById("previewImage").innerHTML=strcode;
         }
    else
       {
          alert("请选择正确的图片文件");
          document.getElementById("FileUp").value="";
        }
     }

</script>

HTML代码：

<table border="0" cellpadding="0" cellspacing="0" width="100%" height="100%" ID="Table1">
<tr>
<td width="255" height="100%" valign="middle">
<INPUT id="FileUp" style="WIDTH: 253px; HEIGHT: 22px" type="file" size="23" name="File1"
runat="server" onchange="checkData()"><br>
&nbsp;&nbsp;注：这里可以是图片（jpg或gif格式）,flash动画（swf）及视频文件（wmv,mpeg,asf,avi）。大小限定在1M以内。
</td>
<td>
<div id="previewImage">当前页预览</div>
</td>
</tr>
</table>