Forms Data Controls :: Check Box Control Inside The Gridview

I wrote simple program in that i have one gridview in that i added one template field Checkbox controll.

this is my gridview1

<asp:GridView ID="GridView1" runat="server" Width="100%" AutoGenerateColumns="False" CellPadding="4" ForeColor="#333333" GridLines="None" OnSelectedIndexChanged="GridView1_SelectedIndexChanged" AllowPaging="True" OnPageIndexChanging="GridView1_PageIndexChanging"
PageSize="20">
<RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
<Columns>
<asp:TemplateField >
<ItemTemplate>
<asp:CheckBox runat="server" Text='<%# DataBinder.Eval( Container.DataItem, "Title") %>' ID="chk1" />
</ItemTemplate>
</asp:TemplateField>
<%-- <asp:BoundField DataField="Title" HeaderText="Title" />--%>
<asp:BoundField DataField="Creation_Date" HeaderText="Creation Date" />
</Columns>
<FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
<SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
<HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<EditRowStyle BackColor="#999999" />
<AlternatingRowStyle BackColor="White" ForeColor="#284775" />
</asp:GridView>

i have one button control in that click event i write some code like this

protected void btndelete_Click(object sender, EventArgs e)
{
CheckBox chk;
for (int i = 0; i < GridView1.Rows.Count; i++)
{
CheckBox cb = (CheckBox)GridView1.Rows[i].Cells[0].FindControl("chk1");
if (cb.Checked)
{
Response.Write("checked");
}
}
}

but when i run this code that check box return vlues every time false when i clicked the checkbox.