Give

<asp:GridView ID="gvResult2" runat="server" CssClass="table-view"
    DataKeyNames="MetadataId" DataSourceID="ObjectDataSource1">
    <RowStyle CssClass="row-item" />
    <Columns>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:CheckBox ID="CheckBox1" runat="server" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="序號">
            <ItemTemplate>
                <%# Container.DataItemIndex + 1 %></ItemTemplate>
        </asp:TemplateField>
    </Columns>
    <FooterStyle CssClass="row-foot" />
    <AlternatingRowStyle CssClass="row-alter" />
</asp:GridView>