datagrid row count in wpf

Hi,

    I have problem to getting datagrid row count in UserControl loaded in wpf...

My coding..

private void UserControl_Loaded(object sender, RoutedEventArgs e)
        {
            viewprojectdetails();
        }

public void viewprojectdetails()
        {
            con = new SqlConnection(cn);
            con.Open();
            SqlCommand cmd = new SqlCommand("viewongoing", con);
            cmd.CommandType = CommandType.StoredProcedure;
            DataTable dt = new DataTable();
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(dt);
            gvproject.DataContext = dt.DefaultView;
            int a = dt.Rows.Count;
            label3.Content = a.ToString();
            //MessageBox.Show(a.ToString());
            con.Close();
           // loadcount();
        }

in message box shows row count as 19 but if i remove that message box the label shows row count as zero..and also i put this coding in button means its shows row count as 19..i dont know why it will not in user control load...