Find Checkbox from GridView in Content Page/Master Page

How to find a control from GridView which resides in Content Page. Here the example using to find the CheckBox, hope this will help you all...

.aspx

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="Server">
    <asp:GridView ID="GridView1" runat="server">
        <Columns>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:CheckBox ID="chkID" runat="server" />
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
</asp:Content>

code behind 

Dim ChkSel As New CheckBox
Dim CellValue As New StringCollection
Dim tmpGV As New GridView
tmpGV = FindControlRecursive(Page.Master, "GridView1")
For i = 0 To tmpGV.Rows.Count - 1
ChkSel = DirectCast(DirectCast(tmpGV.Rows(i), GridViewRow).Cells(0), TableCell).Controls(1)
If ChkSel.Checked = True Then
CellValue.Add(DirectCast(tmpGV.Rows(i), GridViewRow).Cells(1).Text)
End If
Next
private Control FindControlRecursive(Control root, string id)
{
    if (root.ID == id)
    {
     return root;
    }
    foreach (Control c in root.Controls)
    {
        Control t = FindControlRecursive(c, id);
        if (t != null)
        {
            return t;
        }
    }
    return null;
}