GridView and XmlDatasource

[勇敢的心]

I want to display data by gridview which binded to a xmldatasource.
In the .aspx file , I get xml string from a function ,and set

xmldatasource.data=strXml;

When running in browser, there is an error that said the xmldatasource is
empty.

I am using vs.net 2005 beta 2.
How to do?
Thanks!