ASP.NET项目未引用Microsoft.ReportViewer.WebForms却加载失败求助

这种情况我碰到过好几次，明明项目里没加这个引用，却报加载失败的错，大概率是隐性依赖或者配置/部署残留导致的，给你几个实用的排查方向：

• 检查所有配置文件
  直接在整个项目范围内搜索Microsoft.ReportViewer.WebForms，重点看Web.config的<assemblies>节点——很可能之前有人添加过这个引用后来删除了，但配置项没清理干净，或者某个第三方组件的配置自动注入了这个引用。比如有没有类似这样的节点：

  <add assembly="Microsoft.ReportViewer.WebForms, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91" />
  

  同时也要检查<compilation>节点下的程序集集合，以及是否有自定义的handler或module配置用到了这个程序集。

• 排查第三方NuGet包的间接依赖
  有些第三方库（比如旧的报表组件、业务框架）可能会间接依赖ReportViewer。你可以用NuGet包管理器的“查看依赖项”功能逐个检查已安装的包，或者在Package Manager Console里运行以下命令查看所有包的依赖树：

  Get-Package -ProjectName YourProjectName | Select-Object Id, Dependencies
  

  替换YourProjectName为你的项目名称，就能定位到哪个包引入了这个隐性依赖。

• 检查部署环境的残留文件和配置
  如果是部署到IIS后出现的问题，先确认服务器的全局程序集缓存（GAC）里有没有这个版本的程序集；再检查站点根目录的bin文件夹，是不是之前部署过带报表功能的版本，残留了ReportViewer相关的dll文件；另外也要看看IIS应用程序池的配置，有没有加载额外的程序集。

• 检查项目的构建/发布配置
  有时候项目的发布配置文件（.pubxml）里可能指定了要复制这个dll，或者构建事件脚本里自动添加了引用。你可以打开项目的发布配置，检查“文件发布选项”里的内容，或者查看项目属性的“生成事件”标签页。

• 用工具追踪程序集加载路径
  推荐用Visual Studio自带的Fusion Log Viewer（运行fuslogvw.exe）来排查。打开工具后勾选“Enable Logging”，然后重新运行项目，它会记录系统尝试加载这个程序集的所有路径，以及失败原因，帮你精准定位触发加载的源头。

堆栈跟踪信息 #

[FileNotFoundException: Could not load file or assembly 'Microsoft.ReportViewer.WebForms, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies. The system cannot find the file specified.] 
System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0 
System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +457 
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection) +110 
System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +22 
System.Reflection.Assembly.Load(String assemblyString) +34 
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +48 

[ConfigurationErrorsException: Could not load file or assembly 'Microsoft.ReportViewer.WebForms, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies. The system cannot find the file specified.] 
System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +729 
System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +69 
System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +226 
System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies() +73 
System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +321 
System.Web.Compilation.BuildManager.ExecutePreAppStart() +170 
System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +878 

[HttpException (0x80004005): Could not load file or assembly 'Microsoft.ReportViewer.WebForms, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies. The system cannot find the file specified.] 
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +525 
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +124 
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +700 

内容的提问来源于stack exchange，提问作者PongGod