ASP.NET中的gridview为什么不显示，我绑定了数据的

protected void Page_Load(object sender, EventArgs e)
{
string con = "data source=oract;uid=cheng;pwd=abc";
string sqlstr = "select * from tb_students";
oraSqlHelper os = new oraSqlHelper();
DataTable dt = os.getTable(con, sqlstr);
GridView1.DataSource = dt;
GridView1.DataBind();
string sqlstr1 = "select * from tb_cars";
DataTable dt2 = os.getTable(con, sqlstr1);
GridView2.DataSource = dt2;
GridView2.DataBind();
}