making multiple checkbox clickable in datalist

 .aspx


<asp:DataList ID="DataList1" runat="server" RepeatDirection="Horizontal">
        <ItemTemplate>
            <asp:ImageButton ID="ImageButton1" runat="server" ImageUrl="~/load.GIF" OnClick="btn"/>
            <asp:CheckBox ID="CheckBox1" runat="server" />
        </ItemTemplate>
        </asp:DataList>



.cs

 protected void btn(object sender, EventArgs e)
    {  
        ImageButton b1 = (ImageButton)sender;
        DataListItem d1 = (DataListItem)b1.NamingContainer;
        CheckBox chk1 = (CheckBox)DataList1.Items[d1.ItemIndex].FindControl("CheckBox1");
       
        if (chk1.Checked == true)
        {
            chk1.Checked = false;
        }
        else
        {
            chk1.Checked = true;
        }

    }