Raise event of button inside GridView in ASP.Net

<asp:TemplateField HeaderText="Swap">
             <ItemTemplate>
                           <asp:Button ID="btnOk" runat="server"  Text="Ok" Visible="false" OnClick="btnOk_Click" />
            </ItemTemplate>
            <ItemStyle HorizontalAlign="Left"  Wrap="False" />
</asp:TemplateField>


protected void btnOk_Click(object sender, EventArgs e)
    {
        GridViewRow selRow = (GridViewRow)((Button)sender).NamingContainer;
     
        DropDownList ddlUsers = (DropDownList)selRow.FindControl("ddlUsers");

        SwapData(ddlUsers.SelectedValue.ToString()); 

        Button btnOk = (Button)selRow.FindControl("btnOk");
        btnOk.Visible = false;

    }