求教！pull解析xml时eventType = parser.next()无效

代码很短如下：
public String gettext(InputStream input)
    {
        String kk="null";
        try {
            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
            // 获取一个解析实例
            XmlPullParser parser = factory.newPullParser();
            parser.setInput(input, "UTF-8");
            int eventType =parser.getEventType();
            while (eventType != XmlPullParser.END_DOCUMENT)
            {
                switch (eventType)
                {
                    case XmlPullParser.START_DOCUMENT://这句能正常解析，说明已经得到文件开头了啊，怎么以后的标签会得不到
                        kk="lihongyipp";
                        break;
                    case XmlPullParser.START_TAG:
                            kk="lihongyi";
                        break;
                }
                eventType = parser.next();//一到这里while就不继续执行，也不报错，程序输出lihongyipp
                Toast toast = Toast.makeText(this,"下一个",Toast.LENGTH_SHORT);
                toast.show();
            }
}catch(XmlPullParserException e) {
            e.printStackTrace();
        }
        catch(IOException e){
            e.printStackTrace();
        }
        catch(Exception e){
            e.printStackTrace();
        }
        return kk;
    }
}

xml文件：
<?xml version="1.0" encoding="UTF-8"?>
<resources><book>lihongyi</book></resources>

求解怎么回事？谢谢！