Web Forms :: Retrieve Value Of Row When Clicked

 I am using Common field button in each row of a gridview. I am displaying  trainerID,names,mobile numbers .The name of my command field button is View Profile. I want to retrieve the trainer iD  when i Click on the command field b I always get row.Cells[1].Text as null.

protected void GridView1_SelectedIndexChanging(object sender,GridViewSelectEventArgs e)
{
GridViewRow row = (GridViewRow)GridView1.Rows[e.NewSelectedIndex];
Session["contactID"] = row.Cells[1].Text;
Response.RedirectPermanent("~/TrainersDetails.aspx", false);
}