How to implement full selection of datagrid checkbox in asp.net

Copy codeThe Code is as follows: <form runat = "server">
<Asp: DataGrid AutoGenerateColumns = "false" OnItemCreated = "itemcreate" DataKeyField = "link_id" ID = "mydg" runat = "server">
<Columns>
<Asp: TemplateColumn>
<Headertemplate>
<Asp: CheckBox ID = "checkall" OnCheckedChanged = "chkall_onchanged" AutoPostBack = "true" runat = "server"> </asp: CheckBox>
</Headertemplate>
<Itemtemplate>
<Asp: CheckBox ID = "checkdel" runat = "server"> </asp: CheckBox>
</Itemtemplate>
</Asp: TemplateColumn>
<Asp: BoundColumn DataField = "link_id" HeaderText = "Link_Id"> </asp: BoundColumn>
<Asp: BoundColumn HeaderText = "website name" DataField = "sitename"/>
<Asp: BoundColumn HeaderText = "website address" DataField = "url"/>
<Asp: BoundColumn HeaderText = "website Introduction" DataField = "intro"/>
<Asp: BoundColumn HeaderText = "website score" DataField = "grade"/>
<Asp: BoundColumn HeaderText = "submission time" DataField = "submit_date"> </asp: BoundColumn>
</Columns>
</Asp: DataGrid>
<Asp: Label ID = "lb1" runat = "server"> </asp: Label>

<Asp: Button ID = "btn1" Text = "delete" runat = "server" OnClick = "btn1_onclick"> </asp: Button>
<Asp: Button ID = "OK" OnClick = "OK _click" Text = "Save and modify" runat = "server"> </asp: Button>
<Asp: Button ID = "cancel" OnClick = "cancel_click" Text = "unmodify" runat = "server"> </asp: Button>
</Form>


<% @ Import namespace = "system. data" %>
<% @ Import namespace = "system. data. oledb" %>
<Script language = "vb" runat = "server">
Dim conn as oledbconnection
Dim ds as dataset
Sub Page_load (sender as object, e as eventargs)
If not ispostback then
Calldb ()
Else
Ds = session ("ds ")
End if

End sub
Sub calldb ()
Conn = new oledbconnection ("provider = Microsoft. jet. oledb.4.0; data source =" & server. MapPath ("wwwlink. mdb "))
Dim sqlstr = "select * from link"
Conn. open ()
Dim adp as new oledbdataAdapter (sqlstr, conn)
Ds = new dataset ()
Adp. fill (ds, "link ")
Mydg. DataSource = ds. tables ("link"). defaultview
Mydg. databind ()
Conn. close ()
Session ("ds") = ds
End sub
Sub btn1_onclick (sender as object, e as eventargs)
Dim chk as checkbox
Dim id as string
Dim datag as datagriditem
Conn = new oledbconnection ("provider = Microsoft. jet. oledb.4.0; data source =" & server. MapPath ("wwwlink. mdb "))
Dim sqlstr as string
Dim cmd as oledbcommand

Dim I as integer
'For each datag in mydg. items

For I = 0 to mydg. items. count-1
'Chk = ctype (datag. findcontrol ("checkdel"), checkbox)
'Chk = datag. findcontrol ("checkdel ")
Chk = mydg. items (I). cells (0). findcontrol ("checkdel ")
If chk. checked then
Id = cstr (mydg. items (I). cells (1). text)
'Id = cstr (mydg. datakeys (datag. itemindex ))
Conn. open ()
Sqlstr = "delete from link where link_id =" & id
Cmd = new oledbcommand (sqlstr, conn)
Cmd.exe cutenonquery
'Ds. tables ("link"). rows (I). delete ()
Conn. close ()
End if

Next
'Session ("ds") = ds
'Mydg. edititemindex =-1
'Mydg. datasource = ds. tables ("link"). defaultview
'Mydg. databind ()
Calldb ()
End sub
Sub cancel_click (sender as object, e as eventargs)
Calldb ()
End sub

Sub OK _click (sender as object, e as eventargs)
Conn = new oledbconnection ("provider = Microsoft. jet. oledb.4.0; data source =" & server. MapPath ("wwwlink. mdb "))
Dim adp as new oledbdataadapter ("select * from link", conn)
Dim ocb as new oledbcommandbuilder (adp)
Adp. updatecommand = ocb. getupdatecommand ()
Adp. deletecommand = ocb. getdeletecommand ()
Adp. update (ds, "link ")
Calldb ()
End sub
Dim checka as checkbox
Sub itemcreate (sender as object, e as datagriditemeventargs)
If (e. item. itemtype = Listitemtype. Header) then
Checka = e. item. findcontrol ("checkall ")
End if
End sub

Sub chkall_onchanged (sender as object, e as eventargs)

Dim I as integer
If checka. checked = true then
For I = 0 to mydg. items. count-1

Dim chk as checkbox = mydg. items (I). cells (0). findcontrol ("checkdel ")
Chk. checked = true
Next
Else
For I = 0 to mydg. items. count-1
Dim chk as checkbox = mydg. items (I). cells (0). findcontrol ("checkdel ")
Chk. checked = false
Next

End if
End sub
</Script>