<asp:TemplateField>
  <ItemTemplate>
        <asp:Button runat="server" CommandArgument='<%# Eval("ID") %>' CommandName="DoSomething"   ... />
  </ItemTemplate>
</asp:TemplateField>

protected void MyGridView_RowCommand(object sender, GridViewCommandEventArgs e) {
    if (e.CommandName == "DoSomething") {
        int id = Convert.ToInt32(e.CommandArgument);
        ...
    }
}