Can't get Select event at GridView in userControl

Question

I have button and GridView at UserControl. When I press button.It will perform at PageLoad function. But when I click select in GridView.It can't work same button at PageLoad.

 if (!IsPostBack){}             
 else{
                    string str_btn = null;
                    if (Request.Form.Keys[Request.Form.Keys.Count - 1]!=null)
                        str_btn=Request.Form.Keys[Request.Form.Keys.Count - 1].ToString();
                    if(!string.IsNullOrEmpty(str_btn))
                       handleClick(str_btn);
                    else
                        Response.Redirect("../Ipservice/IpserviceDevices.aspx?btn=ipservice", false);
                }

Do you have any solution for resolved this issues.

I wondered if you share your knowledge

IpInterfaceUC UserControl

<div id="dvChannel" runat="server">
        <asp:GridView ID="gvChannelUC" 
            OnRowCommand="gvChannelUC_RowCommand"
            OnSelectedIndexChanged="gvChannel_SelectedIndexChanged"
        />
</div>

IPServices page CodeBehind

if (!IsPostBack){
}else
{    
 string str_btn = Request.Form.Keys[Request.Form.Keys.Count - 1].ToString();
 handleClick(str_btn);
}

Question

It always show str_btn is null.If I click Button,It'll show button's id.But when I click Select at GridView,It show str_btn is null.It should be show GridView's id when we click select.

Thanks for any explain.