我的upload-dialog.js中设置对话框的代码：

  function getDialog()
  {
    if (!dialog) {
      dialog = new Ext.ux.UploadDialog.Dialog({
        url: 'upload-dialog-request.php',
        reset_on_hide: false,
        allow_close_on_upload: true,
        upload_autostart: false, //true,
        post_var_name: 'upload',
		title: '图片上传',
		permitted_extensions:['JPG','jpg','jpeg','JPEG','GIF','gif']
		//minWidth: 400,
		//minHeight: 200,
		//width: 400,
		//height: 350
      });

      dialog.on('uploadsuccess', onUploadSuccess);
			//dialog.on('beforefileuploadstart', onBeforeFileUploadStart);
    }
    return dialog;
  }

upload-dialog-request.php的内容(来自这篇blog:http://zjnbshifox.javaeye.com/blog/123399)：

	$file = "";  
	$result = array();  
	$ext = strrchr($_FILES["file"]["name"],'.');  
	$file = "". date("YmdHis") . $ext;        

	if(move_uploaded_file($_FILES["file"]["tmp_name"],"uploadIDPic/" . $file)){  
		$result = array('success'=>true,data=>$file);  
	}else{  
		$result = array('success'=> false, 'error'=> '文件上传错误');  
	}                 
	echo json_encode($result);  

但是我上传总是失败，我发现upload-dialog-request.php中$ext的值总是为空，感觉这个php程序没有得到上传的文件名，不知道如何解决？