c# - 在 ASP.NET Core 2.0 中使用 KeyFilter

Question

我在简单的 ASP.NET Core 2.0 WebAPI 应用程序中使用 KeyFilter 属性时遇到问题。

<PackageReference Include="Autofac" Version="4.6.1" />
<PackageReference Include="Autofac.Extensions.DependencyInjection" Version="4.2.0" />
<PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.0" />

程序.cs:

public class Program
{
    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
               .ConfigureServices(services => services.AddAutofac())
               .UseStartup<Startup>()
               .Build();
    }

启动.cs:

public Startup(IConfiguration configuration)
{
    Configuration = configuration;
}

public IConfiguration Configuration { get; }

public IContainer ApplicationContainer { get; private set; }

// This method gets called by the runtime. 
// Use this method to add services to the container.
public IServiceProvider ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    // Autofac
    var builder = new ContainerBuilder();

    builder.Populate(services);
    builder.RegisterType<ClassX1>()
           .Keyed<IInterfaceX>("first")
           .WithParameter("name", "X1")
           .SingleInstance();

    builder.RegisterType<ClassX1>()
           .Keyed<IInterfaceX>("second")
           .WithParameter("name", "X2")
           .SingleInstance();

    builder.RegisterType<ClassX1>()
           .As<IInterfaceX>()
           .WithParameter("name", "X3")
           .SingleInstance();

    builder.RegisterType<ValuesController>()
           .WithAttributeFiltering();

    ApplicationContainer = builder.Build();

    return ApplicationContainer.Resolve<IServiceProvider>();
    // return new AutofacServiceProvider(this.ApplicationContainer);
}

// 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.UseMvc();
}

ClassX1.cs:

public class ClassX1: IInterfaceX
{
    public ClassX1(string name)
    {
        Name = name;
    }

    public string Name { get; }
}

IInterfaceX.cs:

public interface IInterfaceX
{
    string Name { get; }
}

ValuesController.cs:

[Route("api/[controller]")]
public class ValuesController : Controller
{
    private readonly IInterfaceX _x;

    public ValuesController([KeyFilter("second")] IInterfaceX x)
    {
        _x = x;
    }

    // GET api/values
    [HttpGet]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2", _x.Name };
    }
}

调用“/api/values”产生 [“value1”，“value2”，“X3”]。但我希望 ["value1","value2","X2"].

如果我删除第三个注册(使用 X3)则

InvalidOperationException: Unable to resolve service for type 'WebApplicationAutofac.IInterfaceX' while attempting to activate 'WebApplicationAutofac.Controllers.ValuesController'.

尝试直接解析工作正确:

var temp = ApplicationContainer.ResolveKeyed<IInterfaceX>("second");

怎么了？

Answer 1

是的，它对 WebAPI Controller 非常有用。

解决方案是添加.AddControllersAsServices():

public IServiceProvider ConfigureServices(IServiceCollection services)
{
    services.AddMvc().AddControllersAsServices();