The first is directly in the Aspx page GridView template column. This has the disadvantage of starting again by page 2.

<asp:TemplateField HeaderText=" The serial number " InsertVisible="False">
<ItemTemplate>
<%#Container.DataItemIndex+1%>
</ItemTemplate>
</asp:TemplateField>

The second method is calculated when paging, which adds up downward.

<asp:TemplateField HeaderText=" The serial number " InsertVisible="False">
<ItemStyle HorizontalAlign="Center" />
<HeaderStyle HorizontalAlign="Center"/>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# this.GridView1.PageIndex * this.GridView1.PageSize + this.GridView1.Rows.Count + 1%>' />
</ItemTemplate>
</asp:TemplateField>

There is another way to put it in the cs code, similar to the second.

<asp:BoundField HeaderText=" The serial number " ></asp:BoundField>
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowIndex != -1)
{
int indexID = this.GridView1.PageIndex * this.myGridView.PageSize + e.Row.RowIndex + 1;
e.Row.Cells[0].Text = indexID.ToString();
}
}