如何在控制器中访问 IApplicationBuilder？

Question

只是想知道，是否可以在 startup.cs 之外访问 IApplicationBuilder 属性？就像在控制器中一样？

我知道它只用于定义应用程序管道，那么解决方案是什么？比如注册一个打包实例的服务，然后注入服务而不是 IApplicationBuilder？

我正在尝试从 Autofac 取回我的 DbConext。代码如下：

在Business 项目中：

 public class AutofacBusinessModule : Autofac.Module
    {
        protected override void Load(ContainerBuilder builder)
        {
            builder.RegisterModule(new AutofacDataModule());
        }
    }

在数据项目中：

 public class AutofacDataModule : Module
    {
        protected override void Load(ContainerBuilder builder)
        {
            builder.RegisterType<AppDbContext>().InstancePerLifetimeScope();
        }
    }

DbContext：

public class AppDbContext : DbContext
    {
        private const string DbContextName = "AppDbConnectionString";
        public DbSet<Contest> Contests { get; set; }

        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
        {
        }

        public AppDbContext()
        {
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (optionsBuilder.IsConfigured) return;

            var configuration = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json")
                .Build();
            var connectionString = configuration.GetConnectionString(DbContextName);
            optionsBuilder.UseSqlServer(connectionString,
                x => x.MigrationsAssembly("Cri.CodeGenerator.Data"));
        }

        public virtual void Commit()
        {
            base.SaveChanges();
        }
    }

还有 ConfigureServices 在 Web 项目中的 startup.cs ：

public IServiceProvider ConfigureServices(IServiceCollection services)
{


    services.Configure<CookiePolicyOptions>(options =>
    {
        // This lambda determines whether user consent for non-essential cookies is needed for a given request.
        options.CheckConsentNeeded = context => true;
        options.MinimumSameSitePolicy = SameSiteMode.None;
    });

    var builder = new ContainerBuilder();

   builder.RegisterModule(new AutofacBusinessModule());


    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();

    services.AddScoped(sp => {
        var actionContext = sp.GetRequiredService<IActionContextAccessor>().ActionContext;
        var urlHelperFactory = sp.GetRequiredService<IUrlHelperFactory>();
        var urlHelper = urlHelperFactory.GetUrlHelper(actionContext);
        return urlHelper;
    });

    services.AddDistributedMemoryCache();
    builder.Populate(services);

    ApplicationContainer = builder.Build();

    //return the IServiceProvider implementation
    return new AutofacServiceProvider(ApplicationContainer);

}

我肯定遗漏了一些东西，但在 DI 和 .net 核心方面确实是新手...

-- 编辑--

在我的Controller

  private readonly IHostingEnvironment _hostingEnvironment;
        private readonly IApplicationBuilder _app;


        private const int NumberOfCharactersRepetion = 4;

        public UniqueCodesController(IHostingEnvironment hostingEnvironment, IApplicationBuilder app)
        {
            _hostingEnvironment = hostingEnvironment;
            _app = app;
        }

...

if (selectedAnswer == FileExtension.XLSX.GetStringValue())
                {
                    await FilesGenerationUtils.GenerateExcelFile(_app, uniqueCodesHashSet, model);
                }

在GenerateExcelFile 方法中：

public static async Task GenerateExcelFile(IApplicationBuilder app, IEnumerable<string> hashSetCodes, ContestViewModel model)
        {
...

 try
                    {
                        var context = app.ApplicationServices.GetRequiredService<AppDbContext>();

                        var contest = new Contest
                        {
                            Name = model.ProjectName,
                            UserId = 1,
                            FileGenerationStatus = true,
                            FilePath = fileInfo.FullName
                        };
                        context.Contests.Add(contest);
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.Message);
                    }

}

但是当我运行应用程序时，我收到了这条消息：

InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Builder.IApplicationBuilder' while attempting to activate 'Cri.CodeGenerator.Web.Controllers.UniqueCodesController'.

Answer 1

听起来您正在尝试获取AppDbContext 的新实例。

如果您必须将GenerateExcelFile() 保留为static 并希望通过参数重用AppDbContext，则可以使其接受AppDbContext 的实例而不是IApplicationBuilder。

首先，直接注入这样一个服务实例：

    private readonly IHostingEnvironment _hostingEnvironment;
    private readonly AppDbContext _dbContext;

    // ...

    public UniqueCodesController(IHostingEnvironment hostingEnvironment, AppDbContext dbContext)
    {
        _hostingEnvironment = hostingEnvironment;
        _dbContext = dbContext;
    }

然后将GenerateExcelFile()改成接受AppDbContext的参数

public static async Task GenerateExcelFile(IApplicationBuilder app, IEnumerablehashSetCodes, ContestViewModel model) 公共静态异步任务 GenerateExcelFile(AppDbContext dbContext, IEnumerable hashSetCodes, ContestViewModel 模型) { ... 尝试{ var context = app.ApplicationServices.GetRequiredService(); var 竞赛 = 新竞赛 { 名称 = 模型.项目名称， 用户 ID = 1， FileGenerationStatus = true, FilePath = fileInfo.FullName }; context.Contests.Add(contest); context.Contests.Add(contest); } 捕捉（例外前） { Console.WriteLine(ex.Message); } }

最后，你可以像下面这样调用它：

    await FilesGenerationUtils.GenerateExcelFile(_dbContext, uniqueCodesHashSet, model);

---

附带说明，如果您无法在编译时确定所需的类型，并且想要动态解析某些服务类型，您可以注入IServiceProvider 而不是IApplicationBuilder。这样，您可以根据需要解析任何实例：

    var dbContext= sp.GetRequiredService<AppDbContext>();
    // or if you need a service only available within a scope 
    using(var scope = this._sp.CreateScope()){
        var _anotherDbContext = scope.ServiceProvider.GetRequiredService<AppDbContext>();
        ...
    }

以您的代码为例，您可以将IServiceProvider 传递给GenerateExcelFile(IServiceProvider sp, IEnumerable<string> hashSetCodes, ContestViewModel model)，在GenerateExcelFile() 方法中，您可以通过以下方式解析AppDbContext：

    public static async Task GenerateExcelFile(IServiceProvider sp, IEnumerable<string> hashSetCodes, ContestViewModel model)
    {
        ...

        var dbContext= sp.GetRequiredService<AppDbContext>();

        try{
            var contest = new Contest
            {
                Name = model.ProjectName,
                UserId = 1,
                FileGenerationStatus = true,
                FilePath = fileInfo.FullName
            };

            dbContext.Contests.Add(contest);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }

    }

Answer 2

不，据我所知这是不可能的。

您必须编写一个中间件（或一些其他代码）来将数据从 IApplicationBuilder 获取到 HttpContext 实例。

然后您可以从控制器内部访问 HttpContext 实例。

希望这会有所帮助。