ASP.NET FileUpload无法接收10MB以上文件的问题求助

原始问题 #

使用asp:FileUpload控件实现文件上传功能，已在web.config中配置允许最大50MB文件上传，但选择10MB以上的文件时，控件无法识别该文件（显示未选择状态），10MB以下的文件可正常显示文件名。后端C#上传脚本尚未触发，问题出在前端控件识别阶段。

web.config配置内容：

<?xml version="1.0" encoding="utf-8"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  https://go.microsoft.com/fwlink/?LinkId=169433
  -->
<configuration>
    <system.web>
        <!-- Traditional API: Register a custom SessionIDManager for BotDetect requests -->
        <compilation targetFramework="4.7.2" debug="false" />
        <httpRuntime targetFramework="4.7.2" maxRequestLength="51200" requestLengthDiskThreshold="51200" executionTimeout="3600"/>
    </system.web>
    <appSettings>
        <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />
        <add key="webpages:Version" value="3.0.0.0" />
        <add key="webpages:Enabled" value="false" />
        <add key="ClientValidationEnabled" value="true" />
        <add key="UnobtrusiveJavaScriptEnabled" value="true" />
    </appSettings>
    <system.codedom>
        <compilers>
            <compiler extension=".cs" language="c#;cs;csharp" warningLevel="4" compilerOptions="/langversion:7.3 /nowarn:1659;1699;1701;612;618" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=3.6.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
            <compiler extension=".vb" language="vb;vbs;visualbasic;vbscript" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008,40000,40008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=3.6.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
        </compilers>
    </system.codedom>
    <system.webServer>
        <security>
            <requestFiltering>
                <requestLimits maxAllowedContentLength="52428800" /><!--50MB-->
            </requestFiltering>
        </security>
        <validation validateIntegratedModeConfiguration="false" />
    </system.webServer>
</configuration>

原FileUpload控件代码：

<div class="u-active-custom-color-4 u-align-center-sm u-align-center-xs u-border-2 u-border-custom-color-4 u-btn u-btn-round u-button-style u-custom-color-6 u-custom-font u-heading-font u-hover-custom-color-5 u-radius-30">
                            <asp:FileUpload ID="FileUploadPpt" runat="server" />
                            <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="FileUploadPpt"
                                ValidationExpression="(.+\.([Pp][Pp][Tt][Xx])|.+\.([Pp][Pp][Tt]))"></asp:RegularExpressionValidator>
                            <asp:Label ID="LabelPptFile" runat="server" Text=""></asp:Label>
                        </div>

用户点击页面末尾的“Create”按钮才会执行后端上传脚本，但目前根本到不了这一步。

临时解决方案 #

尝试多种常规方法无效后，找到一个不太合理的折中方案：添加一个额外的FileUpload控件，放在原控件之前，该新控件可正常接收大文件。但删除原控件只保留新控件无效，最终只能保留两个控件并隐藏第一个控件（通过拆分div块实现，不能直接设置控件的Visible属性，否则会引发新问题）。

修改后的代码如下：

<asp:FileUpload ID="FileUpload2" runat="server" />
                    </div>
                    <div class="u-active-custom-color-2 u-border-2 u-border-white u-btn u-btn-round u-button-style u-custom-color-3 u-custom-font u-heading-font u-hover-custom-color-1 u-radius-30">
                        <asp:FileUpload ID="FileUploadPpt" runat="server" />
                        <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="FileUploadPpt"
                            ValidationExpression="(.+\.([Pp][Pp][Tt][Xx])|.+\.([Pp][Pp][Tt]))"></asp:RegularExpressionValidator>
                        <asp:Label ID="LabelPptFile" runat="server" Text=""></asp:Label>
                    </div>

此方案虽不优雅，但能解决大文件无法被控件识别的问题，分享给遇到相同问题的开发者参考。

内容的提问来源于stack exchange，提问作者starspejd