c# - 如何在 Controller 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 Controller 中一样？

我知道它仅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(inject)服务而不是 IApplicationBuilder？

我正在尝试从 Autofac 取回我的 DbConext。代码如下:

在业务项目中:

 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();
        }
    }

以及Web项目中startup.cs中的ConfigureServices:

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 核心方面真的是新手......

-- 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.

如果您必须保留 GenerateExcelFile()作为static并想重复使用AppDbContext通过一个参数，你可以让它接受 AppDbContext 的实例而不是 IApplicationBuilder .

首先，简单地直接注入(inject)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;
    }

然后更改GenerateExcelFile()接受 AppDbContext 的参数

    
  
   public static async Task GenerateExcelFile(IApplicationBuilder app, IEnumerable<string>hashSetCodes, ContestViewModel model)
      public static async Task GenerateExcelFile(AppDbContext dbContext, IEnumerable hashSetCodes, ContestViewModel model)    {        ...        try{            
  
   var context = app.ApplicationServices.GetRequiredService();
              var contest = new Contest            {                Name = model.ProjectName,                UserId = 1,                FileGenerationStatus = true,                FilePath = fileInfo.FullName            };            
  
   context.Contests.Add(contest);
              context.Contests.Add(contest);        }        catch (Exception ex)        {            Console.WriteLine(ex.Message);        }    }

Finally, you could invoke it as below :

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

---

作为旁注，如果您无法在编译时确定所需的类型，并希望动态解析某些服务类型，您可以注入(inject)一个 IServiceProvider而不是 IApplicationBuilder 。这样，您可以根据需要解决任何实例:

    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，您可以传递 IServiceProvider至 GenerateExcelFile(IServiceProvider sp, IEnumerable<string> hashSetCodes, ContestViewModel model) ，并在 GenerateExcelFile() 内方法，你可以解决 AppDbContext通过以下方式:

    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);
        }

    }