ASP.net RegularExpressionValidator允许回发，即使输入无效

我正在尝试制作一个用于上传图像的表单。我放置了一个RegularExpressionValidator来检查所选文件的扩展名。其ValidationExpression为:

(?i:^.+(.jpg|.ttf|.png|.gif)$)

但是当我选择一个。exe文件为例。页面进行回发，然后显示错误。并且。exe文件被存储在它不应该存储的地方。

这是我的HTML代码的控制:

<%@ Page Title="" Language="C#" MasterPageFile="~/filippo_admin_page/admin_master.Master" AutoEventWireup="true" CodeBehind="a_gallery.aspx.cs" Inherits="photography.filippo_admin_page.a_gallery" %>
    <asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
        <link rel="Stylesheet" type="text/css" href="css/a_gallery.css" />
    </asp:Content>
    <asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
        <div id="whole_wrapper">
            <fieldset>
                <legend>Insert new image:</legend>
                <div id="controls_wrapper">        
                    <ul>
                        <li>
                            <asp:Label AssociatedControlID="title_txt" runat="server" ID="title_lbl">Title:</asp:Label>
                            <asp:TextBox ID="title_txt" runat="server" placeholder="Image title"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
                                ControlToValidate="title_txt" ErrorMessage="RequiredFieldValidator" 
                                ForeColor="Red" ValidationGroup="gallery_validation">Required!</asp:RequiredFieldValidator>
                        </li>
                        <li>
                            <asp:Label AssociatedControlID="desc_txt" runat="server" ID="desc_lbl">Description:</asp:Label>
                            <asp:TextBox ID="desc_txt" runat="server" placeholder="Image description" TextMode="MultiLine"></asp:TextBox>
                        </li>
                        <li>
                            <asp:Label AssociatedControlID="cat_txt" runat="server" ID="cat_lbl">Category:</asp:Label>
                            <asp:TextBox ID="cat_txt" runat="server" placeholder="Image category"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" 
                                ControlToValidate="cat_txt" ErrorMessage="RequiredFieldValidator" 
                                ForeColor="Red" ValidationGroup="gallery_validation">Required!</asp:RequiredFieldValidator>
                        </li>
                        <li>
                            <asp:Label ID="upload_lbl" runat="server">Select Image:</asp:Label>
                            <asp:FileUpload ID="upload_pnl" runat="server" />
                            <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" 
                                ControlToValidate="upload_pnl" ErrorMessage="RequiredFieldValidator" 
                                ForeColor="Red" ValidationGroup="gallery_validation">Required!</asp:RequiredFieldValidator>
                            <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" 
                                ControlToValidate="upload_pnl" ErrorMessage="RegularExpressionValidator" 
                                ForeColor="Red" ValidationExpression="(?i:^.+(.jpg|.ttf|.png|.gif)$)" 
                                ValidationGroup="gallery_validation">File must be an image.</asp:RegularExpressionValidator>
                        </li>
                        <li>
                            <asp:Button ID="clear" runat="server" Text="Clear" UseSubmitBehavior="False" />
                            <asp:Button ID="submit" runat="server" Text="Upload"  onclick="submit_Click" 
                                ValidationGroup="gallery_validation"/>                        
                        </li>
                    </ul>
                </div>
                <asp:Label ID="msg_lbl" Visible="false" runat="server"></asp:Label>
            </fieldset>
        </div>    
    </asp:Content>

这是验证器的部分:

<li>
    <asp:Label ID="upload_lbl" runat="server">Select Image:</asp:Label>
    <asp:FileUpload ID="upload_pnl" runat="server" />
    <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" 
        ControlToValidate="upload_pnl" ErrorMessage="RequiredFieldValidator" 
        ForeColor="Red" ValidationGroup="gallery_validation">Required!</asp:RequiredFieldValidator>
    <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" 
        ControlToValidate="upload_pnl" ErrorMessage="RegularExpressionValidator" 
        ForeColor="Red" ValidationExpression="(?i:^.+(.jpg|.ttf|.png|.gif)$)" 
        ValidationGroup="gallery_validation">File must be an image.</asp:RegularExpressionValidator>
</li>

我有ValidationGroup等于gallery_validation，并设置在我想要验证的所有控件上，包括submit按钮本身。

如果您想要文件的整个HTML代码，请询问。

<asp:RegularExpressionValidator EnableClientScript="true"
ID="RegularExpressionValidator1" runat="server" 
    ControlToValidate="upload_pnl" ErrorMessage="RegularExpressionValidator" 
    ForeColor="Red" ValidationExpression="(?i:^.+(.jpg|.ttf|.png|.gif)$)" 
    ValidationGroup="gallery_validation">File must be an image.</asp:RegularExpressionValidator>