C# 在中继器内时文本框值不改变

我有以下中继器：

<asp:Repeater ID="rprCartItems" runat="server">
    <ItemTemplate>
        <tr class="product-row">

            <asp:HiddenField ID="hfQty" value="0"  runat="server" />
            <td class="product-col">
                <figure class="product-image-container">
                    <a href="product.html" class="product-image">
                    
                    </a>
                </figure>

            </td>
            <td class="td-price">$<span class="price"><%# Container.DataItem("price") %></span></td>
            <td class="tr-quantites">
                <span data-qty="<%# Container.DataItem("quantity") %>" style="display:none"></span>
                <span class="availableQty" style="display:none"><%# Container.DataItem("availableQty") %></span>
                <asp:TextBox CssClass="vertical-quantity form-control" ID="txtQty"   runat="server"></asp:TextBox>
                
            </td>
            <td class="td-total">$<span class="total"><%# Container.DataItem("price") * Container.DataItem("quantity") %></span></td>
        </tr>
        <tr class="product-action-row">
            <td colspan="4" class="clearfix">
            <%--    <div class="float-left">
                    <a href="#" class="btn-move">Move to Wishlist</a>
                </div><!-- End .float-left -->--%>
        
                <div class="float-right">
                    <asp:LinkButton CommandName="remove" CommandArgument='<%# Container.DataItem("id") %>' title="Remove from cart" cssClass="btn-edit text-danger" ID="removeItem" runat="server"><span class="sr-only">Remove</span><i class="fa fa-times"></i></asp:LinkButton>
                    <asp:LinkButton CommandName="update" CommandArgument='<%# Eval("id")  %>' title="Remove from cart" cssClass="btn-edit text-danger" ID="LinkButton1" runat="server"><span class="sr-only">Remove</span><i class="fa fa-times"></i></asp:LinkButton>
                
                </div><!-- End .float-right -->
            </td>
        </tr>
    </ItemTemplate>
</asp:Repeater>

或c#

但是，文本框文本中的更改没有反映出来。如果文本框有一个默认文本，这就是Msgbox中的内容

有什么想法吗

谢谢

<asp:TextBox CssClass="vertical-quantity form-control" ID="txtQty"   runat="server"></asp:TextBox>

    Dim t As TextBox = TryCast(e.Item.FindControl("txtQty"), TextBox)

    MsgBox(t.Text)

TextBox t = e.Item.FindControl("txtQty") as TextBox;