使用 Autofac 4 和 vNext 自注册库

Question

我想为我的 ASP.Net 5.0 / MVC 6 应用程序创建一个插件环境。我使用 Autofac 作为 IOC 容器，我喜欢从 DNX LibraryManager 中的构建加载插件（Class 库）。使用库管理器的目的是，我不必关心 NuGet 包和框架。

我遇到的问题是生命周期，我必须在 LibraryManager 实例可用之前构建 IOC 容器。因为 Autofac 容器提供了他自己的 IServiceProvider 实例，我必须在 ConfigureService() 方法调用 (AddAutofac) 中注入它。

有人知道如何让它工作吗？

更新：我已经在 David 的帮助下解决了我的问题，并更新了代码以使其与发布候选版本一起使用。我还添加了对配置的支持。

在我的 DNX Class 库中，我实现了一个 Class 用于自注册：

public class AutofacModule : Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.Register(c => new SimpleService())
               .As<IService>()
               .InstancePerLifetimeScope();
    }
}

在我的 MVC WebApplication 中，我添加了 Class 库作为依赖项。

Startup.cs

public IConfiguration Configuration { get; set; }

public class Startup
{
    public Startup( IApplicationEnvironment applicationEnvironment )
    {
        IConfigurationBuilder configurationBuilder = new ConfigurationBuilder();
        configurationBuilder.SetBasePath( applicationEnvironment.ApplicationBasePath );

        configurationBuilder.AddJsonFile( "appsettings.json" );
        configurationBuilder.AddJsonFile( "autofac.json" );
        configurationBuilder.AddEnvironmentVariables();

        this.Configuration = configurationBuilder.Build();
    }

    public void ConfigureServices(IServiceCollection services)
    {                       
        services.AddMvc();                                     
        services.AddDependencies();    
    }

    public void Configure(IApplicationBuilder applicationBuilder, IHostingEnvironment hostingEnvironment)
    { 
        applicationBuilder.UseDependencies( this.Configuration );
        applicationBuilder.UseStaticFiles();      
        applicationBuilder.UseMvc();
    }
}

我创建了一个 DependencyResolver 来保留 ContainerBuilder 实例。

DependencyResolver.cs

public class DependencyResolver : IDependencyResolver
{
    private IContainer container;
    private readonly ContainerBuilder builder;     

    public DependencyResolver()
    {
        this.builder = new ContainerBuilder();   
    }

    public void RegisterModule( IModule module )
    {
        this.builder.RegisterModule( module );
    }

    public void RegisterModules( IEnumerable<Assembly> assemblies )
    {         
        this.builder.RegisterAssemblyModules(assemblies.ToArray());  
    }       

    public void Populate( IServiceCollection services)
    {
        this.builder.Populate( services );
    }

    public void Build()
    {
        this.container = this.builder.Build();
    }

    public T Resolve<T>() where T : class
    {                                                 
        return this.container?.Resolve<T>();              
    }      
}

我DependencyResolver.cs

public interface IDependencyResolver
{
    void RegisterModule( IModule module );
    void RegisterModules( IEnumerable<Assembly> assemblies );   
    void Populate(IServiceCollection services);
    void Build();
    T Resolve<T>() where T : class;
}

最后但同样重要的是我创建了一个扩展 Class

DependencyResolverExtensions.cs

public static class DependencyResolverExtensions
{
    public static IServiceCollection AddDependencies( this IServiceCollection services )
    {
        DependencyResolver dependencyResolver = new DependencyResolver();
        dependencyResolver.Populate(services);

        ServiceDescriptor serviceDescriptor = new ServiceDescriptor(typeof ( IDependencyResolver ), dependencyResolver );
        services.TryAdd(serviceDescriptor);

        return services;
    }

    public static IApplicationBuilder UseDependencies(this IApplicationBuilder applicationBuilder, IConfiguration configuration)
    {
        IDependencyResolver dependencyResolver = applicationBuilder.GetService<IDependencyResolver>();
        if (dependencyResolver == null) return applicationBuilder;

        ILibraryManager libraryManager = applicationBuilder.GetService<ILibraryManager>();
        if (libraryManager == null) return applicationBuilder;

        IEnumerable<Assembly> assemblies = libraryManager.GetLoadableAssemblies();
        dependencyResolver.RegisterModules(assemblies);

        ConfigurationModule configurationModule = new ConfigurationModule( configuration );
        dependencyResolver.RegisterModule( configurationModule );

        dependencyResolver.Build();        

        IServiceProvider serviceProvider = dependencyResolver.Resolve<IServiceProvider>();
        applicationBuilder.ApplicationServices = serviceProvider;

        return applicationBuilder;
    }

    public static IEnumerable<Assembly> GetLoadableAssemblies(this ILibraryManager libraryManager)
    {
        List<Assembly> result = new List<Assembly>();    

        IEnumerable<Library> libraries = libraryManager.GetLibraries();    

        IEnumerable<AssemblyName> assemblyNames = libraries.SelectMany(e => e.Assemblies).Distinct();
        assemblyNames = Enumerable.Where(assemblyNames, e => e.Name.StartsWith("MyLib."));

        foreach (AssemblyName assemblyName in assemblyNames)
        {
            Assembly assembly = Assembly.Load(assemblyName);
            result.Add(assembly);
        }

        return result;
    }

    public static T GetService<T>(this IApplicationBuilder applicationBuilder) where T : class
    {
        return applicationBuilder.ApplicationServices.GetService(typeof (T)) as T;
    }
}

如果您需要在不同的实现之间切换，例如模拟数据和真实数据，您可以使用 Autofac 配置。

autofac.json

{
    "components": [
        {
            "type": "MyLib.Data.EF.EntitiesData, MyLib.Data.EF",
            "services": [
                {
                    "type": "MyLib.Abstractions.IDataRepository, MyLib.Abstractions"
                }
            ]
        }
    ]
}

Answer 1

遗憾的是 ConfigureServices 不可注入，这会让这件事变得容易得多。

查看代码，您应该可以安全地替换 Configure(...) 中的 IServiceProvider 而不是 ConfigureServices(...) 中的 IServiceProvider 并获得预期的行为。 ApplicationServices is setable.

在您的 UseAutofac 方法中，您应该能够执行如下操作：

public static IApplicationBuilder UseAutofac( [NotNull] this IApplicationBuilder applicationBuilder )
{
    IAutofacResolver autofacResolver = applicationBuilder.GetService<IAutofacResolver>();
    ILibraryManager libraryManager = applicationBuilder.GetService<ILibraryManager>();

    autofacResolver.RegisterLibraryModules( libraryManager);
    applicationBuilder.ApplicationServices = autofacResolver.Resolve();

    return applicationBuilder;
}

Answer 2

我想出了一个解决方案，它使用了其中的一部分，但也使用了一个 ComponentContainer 来解决 DependencyResolver 中潜在的内存泄漏问题。这也适用于 RC1。还不确定 RC2，因为它不够完整，我无法测试。

ComponentContainer 看起来像这样：

    public static class ComponentContainer {
    static IContainer _container;
    static ContainerBuilder _containerBuilder;

    public static ContainerBuilder Builder {
        get {
            if (_containerBuilder == null)
                _containerBuilder = new ContainerBuilder();
            return _containerBuilder;
        }
    }

    public static IServiceProvider ServiceProvider {
        get {
            if (_container == null)
                _container = _containerBuilder.Build();
            return _container.Resolve<IServiceProvider>();
        }
    }

    public static ComponentFactory<TObject> Component<TObject>() => new ComponentFactory<TObject>(_container);

    public static void RegisterAssembly(Assembly assembly) {
        if (assembly == null) return;

        foreach (var obj in assembly.GetTypes().Where(t => t.GetCustomAttribute<ExportAttribute>() != null)) {
            ExportAttribute att = obj.GetCustomAttribute<ExportAttribute>();
            if (att.ContractType != null) {
                _containerBuilder.RegisterType(obj).As(att.ContractType);
            } else {
                foreach (var intf in obj.GetInterfaces())
                    _containerBuilder.RegisterType(obj).As(intf);
            }
        }
    }
}

public class ComponentFactory<TObject> : IDisposable {
    protected TObject CurrentObject;
    protected ILifetimeScope CurrentScope;
    public TObject Current => (TObject)CurrentObject;
    public ComponentFactory(IContainer container) {
        CurrentScope = container.BeginLifetimeScope();
        CurrentObject = CurrentScope.Resolve<TObject>();
    }

    public TObject Component => CurrentObject;

    public void Dispose() {
        (CurrentObject as IDisposable)?.Dispose();
        CurrentScope.Dispose();
    }
}

然后在 Startup.cs 中我执行以下操作：

    public virtual IServiceProvider ConfigureServices(IServiceCollection services) {
        services.AddMvc();
        services.AddOptions();
        services.AddSession();
        services.AddCaching();

        var assemblyLoadContextAccessor = services.FirstOrDefault(s => s.ServiceType == typeof(IAssemblyLoadContextAccessor)).ImplementationInstance as IAssemblyLoadContextAccessor;
        var libraryManager = services.FirstOrDefault(s => s.ServiceType == typeof(ILibraryManager)).ImplementationInstance as ILibraryManager;

        var loadContext = assemblyLoadContextAccessor.Default;

        foreach(var library in libraryManager.GetLibraries()) {
            var assembly = loadContext.Load(library.Name);

            if(assembly != null) {
                var module = assembly.GetTypes().FirstOrDefault(t => t == typeof(IModule));

                if(module != null)
                    ComponentContainer.Builder.RegisterAssemblyModules(assembly);
                else 
                    ComponentContainer.RegisterAssembly(assembly);                          
            }
        }
        ComponentContainer.Builder.Populate(services);

        return ComponentContainer.ServiceProvider;
    }

要在程序集中导出模块，我要么用 ExportAttribute 标记它们，要么将 class 添加到实现 Autofac 的 IModule 的程序集中。 ConfigureServices 中的代码将枚举应用程序的模块并将它们提供给 ComponentContainer 中的静态 Builder。构建容器后，您可以通过在构造函数中注入来解析模块，也可以通过以下方式请求特定类型：

(using var myComponentFactory = ComponentContainer.Component<IMyModule>()) {
    //You can now access your component through myComponentFactory.Component
    //Once it passes out of scope of using, it will be properly disposed of 
    //along with the scope from which it was created.
}

编辑： 随着 RC2 的发布，此代码不再有效，因为程序集的枚举和 classes 将失败。我还没有想出一个好的解决方案。如果其他人对在 RC2 中枚举程序集有任何建议，请告诉我。

使用 Autofac 4 和 vNext 自注册库

Self-Registering Libraries with Autofac 4 and vNext

c#

dependency-injection

autofac

asp.net-core-mvc

dnx