高分求助（在线等，万分急啊！）：我的DataGrid的数据源是SqlDataReader，DataGrid自定义分页已经设置了VirtualItemCount，为什么点击分

我的DataGrid的数据源是SqlDataReader，DataGrid自定义分页已经设置了VirtualItemCount，为什么点击分页按钮的时候页面没有显示啊？
<asp:datagrid id=DataGrid1 style="Z-INDEX: 119; LEFT: 160px; POSITION: absolute; TOP: 232px" runat="server" Width="700px" DataSource="<%# dreader %>" AllowPaging="True" BorderColor="#6595D6" BorderStyle="None" BorderWidth="1px" BackColor="White" CellPadding="4" PageSize="6" AllowCustomPaging="True" OnPageIndexChanged="DataGrid1_PageIndexChanged" OnSelectedIndexChanged="DataGrid1_SelectedIndexChanged">
<FooterStyle ForeColor="Black" BackColor="#6595D6"></FooterStyle>
<SelectedItemStyle Font-Bold="True" ForeColor="Black" BackColor="#009999"></SelectedItemStyle>
<ItemStyle ForeColor="Black" BackColor="White"></ItemStyle>
<HeaderStyle Font-Bold="True" ForeColor="White" BackColor="#6595D6"></HeaderStyle>
<PagerStyle NextPageText="下一页" PrevPageText="上一页" HorizontalAlign="Left" ForeColor="White" BackColor="#6595D6"
Mode="NumericPages"></PagerStyle>
</asp:datagrid>
this.DataGrid1.PageIndexChanged += new System.Web.UI.WebControls.DataGridPageChangedEventHandler(this.DataGrid1_PageIndexChanged);
this.DataGrid1.SelectedIndexChanged += new System.EventHandler(this.DataGrid1_SelectedIndexChanged);public void  DataGrid1_PageIndexChanged(object source, System.Web.UI.WebControls.DataGridPageChangedEventArgs e)
{
sqlConnection1.Open();
dreader3 = sqlCommand3.ExecuteReader(CommandBehavior.SingleRow);
if (dreader3.Read())
{
DataGrid1.VirtualItemCount = (int)dreader3["mycount"];
}
dreader3.Close();
startIndex = e.NewPageIndex * DataGrid1.PageSize;
DataGrid1.CurrentPageIndex = e.NewPageIndex;
DataGrid1.DataBind();
sqlConnection1.Close();
} public void DataGrid1_SelectedIndexChanged(object sender, System.EventArgs e)
{
}