目前在学习ASP.NET CORE MVC中，今天看到微软在ASP.NET CORE MVC 2.0中又恢复了允许开发人员引用第三方DLL程序集的功能，感到甚是高兴！于是我急忙写了个Demo想试试，我的项目结构如下：
可以看到解决方案中就两个项目，AspNetCoreWebApp就是一个ASP.NET CORE MVC 2.0的项目，而MyNetCoreLib是一个.Net Core 2.0的类库项目，为了体现AspNetCoreWebApp是通过程序集来引用MyNetCoreLib的，我还在解决方案中创建了一个文件夹叫Reference，将类库项目MyNetCoreLib编译后生成的DLL文件放到了Reference文件夹中，然后再AspNetCoreWebApp中通过添加引用程序集的方式引用了MyNetCoreLib.dll，如下图所示：
然后编译整个解决方案，调试AspNetCoreWebApp这个项目，运行立马报错。。。错误如下：
这明显是一个运行时错误，因我在编译整个解决方案的时候是成功的，没有报任何错误。后来去网上查了查资料，发现虽然我们在项目AspNetCoreWebApp中引用了MyNetCoreLib.dll，而且项目AspNetCoreWebApp编译后也在其Bin目录下输出了MyNetCoreLib.dll这个文件，如下图所示：
但是ASP.NET CORE MVC的依赖注入环境其实并不知道该到哪里去找MyNetCoreLib.dll这个文件，所以才会在运行时报出InvalidOperationException: Cannot find compilation library location for package ‘MyNetCoreLib‘这种错误。。。开发人员需要用代码去告诉ASP.NET CORE MVC应该到哪里去找到MyNetCoreLib.dll这个文件。
因此首先我们需要定义一个叫MetadataReferenceFeatureProvider的类，代码如下，其关键代码就是告诉ASP.NET CORE MVC的依赖注入环境去AppDomain.CurrentDomain.BaseDirectory（也就是Bin目录）下找我们在项目中引用的程序集文件
using Microsoft.AspNetCore.Mvc.ApplicationParts;using Microsoft.AspNetCore.Mvc.Razor.Compilation;using Microsoft.CodeAnalysis;using Microsoft.Extensions.DependencyModel;using System;using System.Collections.Generic;using System.IO;using System.Linq;using System.Reflection.PortableExecutable;using System.Threading.Tasks;namespace AspNetCoreWebApp.Utils{ ???public class ReferencesMetadataReferenceFeatureProvider : IApplicationFeatureProvider<MetadataReferenceFeature> ???{ ???????public void PopulateFeature(IEnumerable<ApplicationPart> parts, MetadataReferenceFeature feature) ???????{ ???????????var libraryPaths = new HashSet<string>(StringComparer.OrdinalIgnoreCase); ???????????foreach (var assemblyPart in parts.OfType<AssemblyPart>()) ???????????{ ???????????????var dependencyContext = DependencyContext.Load(assemblyPart.Assembly); ???????????????if (dependencyContext != null) ???????????????{ ???????????????????foreach (var library in dependencyContext.CompileLibraries) ???????????????????{ ???????????????????????if (string.Equals("reference", library.Type, StringComparison.OrdinalIgnoreCase)) ???????????????????????{ ???????????????????????????foreach (var libraryAssembly in library.Assemblies) ???????????????????????????{ ???????????????????????????????//告诉ASP.NET CORE MVC如果现在项目中有引用第三方程序集，要到AppDomain.CurrentDomain.BaseDirectory这个文件夹（就是Bin目录）下去寻找该程序集的dll文件 ???????????????????????????????libraryPaths.Add(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, libraryAssembly)); ???????????????????????????} ???????????????????????} ???????????????????????else ???????????????????????{ ???????????????????????????foreach (var path in library.ResolveReferencePaths()) ???????????????????????????{ ???????????????????????????????libraryPaths.Add(path); ???????????????????????????} ???????????????????????} ???????????????????} ???????????????} ???????????????else ???????????????{ ???????????????????libraryPaths.Add(assemblyPart.Assembly.Location); ???????????????} ???????????} ???????????foreach (var path in libraryPaths) ???????????{ ???????????????feature.MetadataReferences.Add(CreateMetadataReference(path)); ???????????} ???????} ???????private static MetadataReference CreateMetadataReference(string path) ???????{ ???????????using (var stream = File.OpenRead(path)) ???????????{ ???????????????var moduleMetadata = ModuleMetadata.CreateFromStream(stream, PEStreamOptions.PrefetchMetadata); ???????????????var assemblyMetadata = AssemblyMetadata.Create(moduleMetadata); ???????????????return assemblyMetadata.GetReference(filePath: path); ???????????} ???????} ???}}其次我们还要在项目AspNetCoreWebApp的Startup.cs文件中的services.AddMvc()方法上注册我们定义的这个Provider，代码如下（注意ConfigureServices方法中的代码）：
using System;using System.Collections.Generic;using System.Linq;using System.Threading.Tasks;using Microsoft.AspNetCore.Builder;using Microsoft.AspNetCore.Hosting;using Microsoft.Extensions.Configuration;using Microsoft.Extensions.DependencyInjection;using Microsoft.AspNetCore.Mvc.Razor.Compilation;using AspNetCoreWebApp.Utils;namespace AspNetCoreWebApp{ ???public class Startup ???{ ???????public Startup(IConfiguration configuration) ???????{ ???????????Configuration = configuration; ???????} ???????public IConfiguration Configuration { get; } ???????// This method gets called by the runtime. Use this method to add services to the container. ???????public void ConfigureServices(IServiceCollection services) ???????{ ???????????services.AddMvc().ConfigureApplicationPartManager(manager => ???????????{ ???????????????//移除ASP.NET CORE MVC管理器中默认内置的MetadataReferenceFeatureProvider，该Provider如果不移除，还是会引发InvalidOperationException: Cannot find compilation library location for package ‘MyNetCoreLib‘这个错误 ???????????????manager.FeatureProviders.Remove(manager.FeatureProviders.First(f => f is MetadataReferenceFeatureProvider)); ???????????????//注册我们定义的ReferencesMetadataReferenceFeatureProvider到ASP.NET CORE MVC管理器来代替上面移除的MetadataReferenceFeatureProvider ???????????????manager.FeatureProviders.Add(new ReferencesMetadataReferenceFeatureProvider()); ???????????}); ???????} ???????// This method gets called by the runtime. Use this method to configure the HTTP request pipeline. ???????public void Configure(IApplicationBuilder app, IHostingEnvironment env) ???????{ ???????????if (env.IsDevelopment()) ???????????{ ???????????????app.UseDeveloperExceptionPage(); ???????????????app.UseBrowserLink(); ???????????} ???????????else ???????????{ ???????????????app.UseExceptionHandler("/Home/Error"); ???????????} ???????????app.UseStaticFiles(); ???????????app.UseMvc(routes => ???????????{ ???????????????routes.MapRoute( ???????????????????name: "default", ???????????????????template: "{controller=Home}/{action=Index}/{id?}"); ???????????}); ???????} ???}}然后重新编译代码，调试项目AspNetCoreWebApp，好了这下项目成功运行了，没有报任何错误。
也不知道本文讨论的这个问题是ASP.NET CORE MVC 2.0的一个缺陷，会在以后版本中修复，还是微软故意为之？因为我试了下在.NET CORE 2.0的控制台项目中，直接引用第三方程序集DLL文件是完全没问题的，不需要写任何额外的代码就可以使用。既然微软在ASP.NET CORE MVC中也开放了引用第三方程序集这个功能，其实就完全可以把它做的和老.Net Framework一样，自动去Bin目录下面寻找DLL文件即可，希望ASP.NET CORE MVC以后的版本能够完善这个功能，不再需要开发人员在引用DLL文件后，还要添加额外的代码。
ASP.NET CORE MVC 2.0 项目中引用第三方DLL报错的解决办法 - InvalidOperationException: Cannot find compilation library location for package
原文地址：http://www.cnblogs.com/OpenCoder/p/8052693.html