SQLDataSource And Updating SelectCommand With Parameters

I have a vb.net application that I want to dynamically create a search criteria using a SQLDataSource. I was trying to dynamically generate a select statement with parameters, assign that string to the selectCommand for the SQLDataSource then selectively assign the parameters.

The issue is several fields (user id) (user name) (email addr)... that I wanted to allow the user to enter any number of these and construct the select given what they entered.

That works if I just construct the string. But I want to use parameters for some sql injection protection as that page will be viewable on the internet.

What happens is I assign the select command but the SqlDataSource does not pick up that there are now some parameters that were not there before.

as in.
Dim firstName As String = tbFirstName.Text
Dim userName As String = tbUserName.Text
Dim userIdFlag As Boolean = False

[Code].....