Can a datareader be stored in a viewstate?
What data can be stored in viewstate?
Any data [serializable] that you need to access during postbacks can be stored in a ViewState.
A DataReader cannot be serialised because is is based on Connected model. So it can't be stored in ViewState.
Also storing huge datatables in ViewState is not advisable. Return only necessary data that you need to show in the current context.