input file 兼容浏览器写法

<style type="text/css">
.ifile {position:absolute;opacity:0;filter:alpha(opacity=0);}
</style>
<form  method="post">
 <input type="file" name="file" id="file" size="20" class="ifile" onchange="upfile.value=this.value"/>
 <input type="text" name="upfile" size="20" readonly/>
 <input type="button" value="选择上传文件"/>
 <input type="Submit" name="Submit" value="上传"/>
</form>