好吧，我想我已经找到了.我这样称呼我的页面-mywebpage.aspx?id = 1，其中id = 1是我要显示Webpart的列表中项目的ID.由于只有Microsoft知道的某些原因，在查询字符串中使用'id'是不可以的.因此，我将参数名称更改为"lid"，现在一切正常.

Well, I think I've found it. I was calling my page like this - mywebpage.aspx?id=1, where id=1 was the id of the item in the list I wanted my webpart to display. For some reason known only to Microsoft, using 'id' in the query string is a no-no. So I changed the param name to 'lid' and now everything works like I would expect.

感谢大家的回应.