Définir et récupérer la valeur de HiddenField dans Gridview

J'ai un contrôle personnalisé qui est incorporé dans un GridView. Le contrôle a besoin d'une valeur (colonne Id de SqlDataSource1) contenue dans le tableau de données que le contrôle gridview est lié à la pour son constructeur.

Le problème que je rencontre est que je ne comprends pas comment définir la valeur du champ caché. Le type de données pour ce champ est un Guid.

ASPX:

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="GridUserControl.ascx.cs" Inherits="CustomNavi_V1_ControlTest.CustomControls.GridUserControl" %>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:srsfwa1_scrambledConnectionString %>" SelectCommand="SELECT [ApplicantId], [ValleyId], [SchoolId], [StatusId], [StudentID], [InterviewDate], [Id] FROM [tblSubmissions]"></asp:SqlDataSource>
<asp:GridView ID="StudentGridView" DataKeysNames="Submission" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1" OnDataBound ="StudentGridView_OnDataBind">
<Columns>
    <asp:BoundField DataField="ApplicantId" HeaderText="ApplicantId" SortExpression="ApplicantId" />
    <asp:BoundField DataField="ValleyId" HeaderText="ValleyId" SortExpression="ValleyId" />
    <asp:BoundField DataField="SchoolId" HeaderText="SchoolId" SortExpression="SchoolId" />
    <asp:BoundField DataField="StudentID" HeaderText="StudentID" SortExpression="StudentID" />
    <asp:BoundField DataField="InterviewDate" HeaderText="InterviewDate" SortExpression="InterviewDate" />
    <asp:BoundField DataField="StatusId" HeaderText="StatusId" SortExpression="StatusId" visible="true"/>
    <asp:BoundField DataField="Id" Visible ="false" />
    <asp:TemplateField>
        <ItemTemplate>
            <asp:HiddenField ID="HiddenField" DataField="SubmissionID" runat="server" Value=""/>
        </ItemTemplate>
    </asp:TemplateField>
    <asp:TemplateField Visible="true" HeaderText="Ed's Fabulous Custom Control!!" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center">
        <ItemTemplate>

        </ItemTemplate>
    </asp:TemplateField>

</Columns>
</asp:GridView>

HiddenField:

protected void AddCustomControl()
{
    int iterator = 0;
    foreach (GridViewRow row in StudentGridView.Rows)
    {
        if (row.RowType == DataControlRowType.DataRow)
        {
            //StudentGridView.HiddenField.value= StudentGridView.
            //HiddenField hiddenField = this.StudentGridView1.FindControl("
            Guid submissionIdGuid = (Guid)hiddenField.Value; //("SubmissionID").Value;
            string controlID = "NavigatorControlID" + iterator.ToString();
            string submissionID = row.Cells[6].Text;  //tblSubmissions Id field
            string statusId = row.Cells[5].Text; //tblSubmissions StatusId field
            connection = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["srsfwa1_scrambledConnectionString"].ToString());

            CustomNavi_V1._1.CustomNavi_V1 navigator = new CustomNavi_V1._1.CustomNavi_V1(submissionID, statusId);
            navigator.ID = controlID;
            navigator.SubmissionID = submissionIdGuid;
            navigator.BackButtonImage = "Images/back_button.png";
            navigator.ForwardButtonImage = "Images/fwd_button.png";

            row.Cells[7].Controls.Add(navigator);
            iterator++;
        }
    }
}