单击按钮时动态添加的文本框为空

我正在动态添加TextBoxes，当我单击提交按钮并进行回发时，我看不到输入到TextBoxes中的值，所有值都会出现emtpy。这是.aspx页面…''

form id="form1" runat="server">
        <asp:PlaceHolder ID="phFormContent" runat="server">
        </asp:PlaceHolder>
        <br /><br />
        <asp:Button ID="btnAddForm" runat="server" Text="Add Form" OnClick="btnAddForm_Click" />
        <asp:Button ID="btnSubmitForms" runat="server" Text="Submit Forms" OnClick="btnSubmit_Click" />
    </form>

以下是我如何在单击"添加表单"时将文本框添加到表单中。。。

protected void btnAddForm_Click(object sender, EventArgs e)
        {
            // Create Labels
            Label lblName = new Label();
            lblName.Text = "NAME:";
            Label lblNumber = new Label();
            lblNumber.Text = "NUMBER:";
            Label lblAddress = new Label();
            lblAddress.Text = "ADDRESS:";
            Label lblCompany = new Label();
            lblCompany.Text = "COMPANY:";
            // Create Text Boxes
            TextBox txtName = new TextBox();
            TextBox txtNumber = new TextBox();
            TextBox txtAddress = new TextBox();
            TextBox txtCompany = new TextBox();
            // Create submit button
            Button btnSubmit = new Button();
            btnSubmit.Text = "SUBMIT";
            // Create panel and add controls
            Panel pnlForm = new Panel();
            pnlForm.Controls.Add(lblName);
            pnlForm.Controls.Add(txtName);
            pnlForm.Controls.Add(new LiteralControl("<br /><br />"));
            pnlForm.Controls.Add(lblNumber);
            pnlForm.Controls.Add(txtNumber);
            pnlForm.Controls.Add(new LiteralControl("<br /><br />"));
            pnlForm.Controls.Add(lblAddress);
            pnlForm.Controls.Add(txtAddress);
            pnlForm.Controls.Add(new LiteralControl("<br /><br />"));
            pnlForm.Controls.Add(lblCompany);
            pnlForm.Controls.Add(txtCompany);
            pnlForm.Controls.Add(new LiteralControl("<hr />"));
            pnlForm.Controls.Add(new LiteralControl("<br /><br />"));
            panels.Add(pnlForm);
            foreach (Control panel in panels)
            {
                phFormContent.Controls.Add(panel);
            }
        }

下面是我如何提取每个单独添加的面板的字段。。。

private static void GetFormFields(Control panelControl)

   {
        ControlCollection controls = panelControl.Controls;
        foreach (Control childControl in panelControl.Controls)
        {
            if (childControl.GetType().ToString() == "System.Web.UI.WebControls.TextBox")
            {
                TextBox txt = childControl as TextBox;
                fields.Add(txt);
            }
            else
            {
                GetFormFields(childControl);
            }
        }
    }

面板和字段是静态列表，每个面板包含四个字段。我向GetFormFields传递一个单独的面板引用。。。

private static List<Control> panels = new List<Control>();
        private static List<TextBox> fields = new List<TextBox>();