In Asp.net, batch Delete the gridview after all selections

<Form ID = "form1" runat = "server">
<Asp: button id = "delall" runat = "server" text = "delete selected" onclick = "delall_click"/>
<Div>
<Asp: gridview id = "gvuser" runat = "server"
Autogeneratecolumns = "false" datakeynames = "userid"
Performanceid = "objectperformanceuser" onrowdeleted = "gvuser_rowdeleted"
Cellpadding = "4" forecolor = "#333333" gridlines = "NONE" allowpaging = "true"
Pagesize = "3">
<Alternatingrowstyle backcolor = "white" forecolor = "#284775"/>

<Columns>
<Asp: templatefield>
<Headertemplate>
<Input id = "checkall" type = "checkbox" onclick = "selectall (this);"/> select all
</Headertemplate>
<Itemtemplate>
<Asp: checkbox runat = "server" id = "checksingle"/>
</Itemtemplate>
<Itemstyle width = "100px"/>

</ASP: templatefield>

<Asp: boundfield datafield = "userid" headertext = "userid"
Sortexpression = "userid"/>
<Asp: boundfield datafield = "username" headertext = "username"
Sortexpression = "username"/>
<Asp: boundfield datafield = "userpass" headertext = "userpass"
Sortexpression = "userpass"/>
<Asp: boundfield datafield = "role" headertext = "role" sortexpression = "role"/>
<Asp: boundfield datafield = "regtime" headertext = "regtime"
Sortexpression = "regtime"/>
<Asp: boundfield datafield = "lognum" headertext = "lognum"
Sortexpression = "lognum"/>
<% -- <Asp: commandfield showeditbutton = "true"/> -- %>
<Asp: templatefield>
<Edititemtemplate>
<Asp: linkbutton id = "linkbutton4" runat = "server" commandname = "Update"> Update </ASP: linkbutton>
<Asp: linkbutton id = "linkbutton5" runat = "server" commandname = "cancel"> cancel </ASP: linkbutton>
</Edititemtemplate>
<Itemtemplate>
<Asp: linkbutton id = "linkbutton3" runat = "server" commandname = "edit"> edit </ASP: linkbutton>
</Itemtemplate>
</ASP: templatefield>
<Asp: templatefield headertext = "operation" showheader = "false">
<Itemtemplate>
<Asp: linkbutton id = "lbdelete" runat = "server" causesvalidation = "false"
Onclientclick = "Return confirm ('Are you sure you want to delete it? ') "Text =" delete "commandname =" delete "> </ASP: linkbutton>
</Itemtemplate>
<Headerstyle forecolor = "# 0033cc"/>
<Itemstyle horizontalalign = "center" verticalalign = "Middle"/>
</ASP: templatefield>
</Columns>
<Editrowstyle backcolor = "#999999" type = "regxph" text = "yourobjectname"/>
<Footerstyle backcolor = "# 5d7b9d" font-bold = "true" forecolor = "white"/>
<Headerstyle backcolor = "black" font-bold = "true" forecolor = "white"/>
<Pagerstyle backcolor = "#284775" forecolor = "white" horizontalalign = "center"/>
<Rowstyle backcolor = "# f7f6f3" forecolor = "#333333"/>
<Selectedrowstyle backcolor = "# e2ded6" font-bold = "true" forecolor = "#333333"/>
<Sortedascendingcellstyle backcolor = "# e9e7e2"/>
<Sortedascendingheaderstyle backcolor = "# 506c8c"/>
<Sorteddescendingcellstyle backcolor = "# fffdf8"/>
<Sorteddescendingheaderstyle backcolor = "# 6f8dae"/>
</ASP: gridview>
<Asp: objectdatasource id = "objectperformanceuser" runat = "server"
Dataobjecttypename = "user" deletemethod = "deleteuser" insertmethod = "adduser"
Selectmethod = "getallusers" typename = "userservice" updatemethod = "modifyuser">
</ASP: objectdatasource>
</Div>
</Form>
<SCRIPT type = "text/JavaScript">
Function selectall (OBJ ){
VaR chkall = OBJ;
State = chkall. checked;
ELEM = chkall. Form. elements;
For (I = 0; I <ELEM. length; I ++ ){
If (ELEM [I]. type = "checkbox" & ELEM [I]! = Chkall. ID ){
If (ELEM [I]. Checked! = State ){
ELEM [I]. Click ();
}
}
}
}

</SCRIPT>

Protected void delall_click (Object sender, eventargs E)
{
Int intcount = This. gvuser. Rows. count;
For (INT I = 0; I <intcount; I ++)
{
Checkbox checksingle = This. gvuser. Rows [I]. cells [0]. findcontrol ("checksingle") as checkbox;
If (checksingle. Checked)
{
Userservice. deleteuserbyuserid (convert. toint16 (this. gvuser. datakeys [I]. Values [0]);
}
}
// Update after deletion
Gvuser. databind ();
}