Unity HoloLens2项目添加包后遇System.Web.HttpUtility缺失错误求助

问题描述 #

原本部署正常的HoloLens 2 Unity 3D AR项目，添加一款用于空间定位QR码的包后，出现以下问题：

• 构建成功但项目无法在设备上运行
• HoloLens未弹出相机权限请求，无任何反应
• 共出现15个编译错误，核心为System.Web.HttpUtility相关类型/方法在目标框架中不存在的引用错误

错误日志示例 #

Reference rewriter: Error: type `System.Web.HttpUtility` doesn't exist in target framework. It is referenced from RestSharp.dll at System.String RestSharp.Extensions.StringExtensions::HtmlDecode(System.String).
UnityEngine.Debug:LogError (object)
PostProcessWinRT:RunReferenceRewriter () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessWinRT.cs:1219)
PostProcessWinRT:Process () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessWinRT.cs:209)
UnityEngine.GUIUtility:ProcessEvent (int,intptr)

Reference rewriter: Error: method `System.String System.Web.HttpUtility::HtmlDecode(System.String)` doesn't exist in target framework. It is referenced from RestSharp.dll at System.String RestSharp.Extensions.StringExtensions::HtmlDecode(System.String).
UnityEngine.Debug:LogError (object)
PostProcessWinRT:RunReferenceRewriter () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessWinRT.cs:1219)
PostProcessWinRT:Process () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessWinRT.cs:209)
UnityEngine.GUIUtility:ProcessEvent (int,intptr)

Reference rewriter: Error: method `System.Collections.Specialized.NameValueCollection System.Web.HttpUtility::ParseQueryString(System.String)` doesn't exist in target framework. It is referenced from RestSharp.dll at RestSharp.Authenticators.OAuth.OAuthWebQueryInfo RestSharp.Authenticators.OAuth.OAuthWorkflow::BuildProtectedResourceInfo(System.String,RestSharp.Authenticators.OAuth.WebParameterCollection,System.String).
UnityEngine.Debug:LogError (object)
PostProcessWinRT:RunReferenceRewriter () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessWinRT.cs:1219)
PostProcessWinRT:Process () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessWinRT.cs:209)
UnityEngine.GUIUtility:ProcessEvent (int,intptr)

已尝试的无效解决方案 #

• 将API兼容性从.NET 4.x改为.NET Standard 2.0：导致更严重错误，无法完成构建
• 添加csc.rps文件并写入-r:System.Web.dll：无效果
• 修改csc.rps文件内容：无变化

当前环境 #

• Unity版本：2019.4.24f1（无法更换）
• Unity构建设置：ARM64、D3D
• 部署方式：Visual Studio 2019，以Master、ARM64、Device模式部署到HoloLens 2

解决方案 #

1. 处理RestSharp的UWP兼容问题 #

错误根源是新增包引入的RestSharp.dll依赖了仅属于.NET Framework桌面类库的System.Web.HttpUtility，而HoloLens使用的UWP框架不包含该类库：

• 若项目实际未用到RestSharp的OAuth或HTML解码功能，直接删除项目中的RestSharp.dll文件
• 若必须保留RestSharp，替换为针对.NET Standard 2.0编译、移除了System.Web依赖的版本（需适配Unity 2019.4的兼容要求）

2. 通过link.xml跳过无效引用检查 #

保持API兼容性为**.NET 4.x**，在Unity项目根目录创建link.xml文件，添加以下内容，指导Unity的引用重写器忽略System.Web相关的缺失引用：

<linker>
  <assembly fullname="RestSharp">
    <type fullname="RestSharp.Extensions.StringExtensions" preserve="all"/>
    <type fullname="RestSharp.Authenticators.OAuth.OAuthWorkflow" preserve="all"/>
  </assembly>
  <assembly fullname="System.Web" ignore="true"/>
</linker>

3. 修复相机权限配置 #

项目无法弹出相机权限请求，大概率是权限配置被新增包覆盖：

• 打开Unity的Player Settings → Publishing Settings → Capabilities，确保勾选Webcam权限
• 构建后在Visual Studio项目中打开Package.appxmanifest，确认包含以下权限声明：

<DeviceCapability Name="webcam"/>

4. 清理缓存后重新构建 #

• 删除Unity项目的Library、Temp文件夹，清理本地缓存
• 在Visual Studio中执行Clean Solution，再重新生成并部署项目

内容的提问来源于stack exchange，提问作者user168356