Filter Data And Update GridView

I have a GridView that gets data from an SqlDataSource. It works fine, but now when I want to filter the results and add more parameters to my sql query, nothing happens. My initial select statement in the SqlDataSource contains only 2 parameters, so now when a user clicks a Button, onclick I call a function that is supposed to change the select statement of the SqlDataSource, add 2 more parameters taken from 2 controls, and then update the GridView. This is what I use: dataSource.SelectCommand = "new select command here";  dataSource.SelectParameters.Add("State", txtState.Text); dataSource.SelectParameters.Add("City", txtCity.Text);  grid.DataBind(); It compiles, but when I click the button to filter the results, the GridView always looks the same as if nothing happened. I do not know if this is the right way to do it, or am I on the wrong track? Help is appreciated. Thank you in advance.