Get DataKey value on check box checked event in a GridView

Here is the .aspx code for the following:-

  <asp:GridView ID="grdTest" runat="server" AutoGenerateColumns="False" DataKeyNames="ID">
    <Columns>
    <asp:TemplateField HeaderText="Is Released" >
     <ItemTemplate>
    <asp:CheckBox ID="chkReleased" runat="server" OnCheckedChanged="chkReleased&#95;CheckedChanged" AutoPostBack="true" />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Write the following code on C# page.

 protected void chkReleased_CheckedChanged(object sender, EventArgs e)
    {
    CheckBox chkreleased = (CheckBox)sender;
    GridViewRow row = (GridViewRow)chkreleased.NamingContainer;
    string Id = grdTest.DataKeys[row.RowIndex].Value.ToString();
  }