Why does ObjectDataSource send an empty DataObjectTypeName to UpdateMethod?

Question

I'm trying to use an ObjectDataSource with a custom DataObjectTypeName (Person), and an UpdateMethod (PersonManager.Instance.Update(Person p))

I'm using a GridView for display, and each column in the GridView has an EditItemTemplate.

My problem is that the ObjectDataSource is sending an empty Person object to my UpdateMethod.

Am I supposed to fill in the Person fields (like Person.name etc) at some point using an event, or should it be filled for me automatically? If I should fill it, at what point?

If I should fill it on ObjectDataSource .OnUpdating method, how do I get the values to update from the GridView? (Since my ObjectDataSourceMethodEventArgs do not contain a RowUpdatingIndex).

Please help!