ASP。Net Core MVC依赖项注入不工作

Question

我试图注入一个接口到我的HomeController，我得到这个错误：

InvalidOperationException：无法解析类型“Microsoft”的服务。扩展。配置尝试激活时的IConfiguration

我的创业课程如下：

public Startup(IApplicationEnvironment appEnv)
{
    var builder = new ConfigurationBuilder()
        .SetBasePath(appEnv.ApplicationBasePath)
        .AddEnvironmentVariables()
        .AddJsonFile("appsettings.json");
    Configuration = builder.Build();
}

public IConfigurationRoot Configuration { get; set; }

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddApplicationInsightsTelemetry(Configuration);

    services.AddEntityFramework()
        .AddSqlServer()
        .AddDbContext<ApplicationDbContext>(options => options
            .UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]));

    services.AddIdentity<ApplicationUser, IdentityRole>()
        .AddEntityFrameworkStores<ApplicationDbContext>()
        .AddDefaultTokenProviders();

    services.AddMvc();
    services.AddSingleton(provider => Configuration);

    // Add application services.
    services.AddTransient<IEmailSender, AuthMessageSender>();
    services.AddTransient<ISmsSender, AuthMessageSender>();
}

public void Configure(
    IApplicationBuilder app, 
    IHostingEnvironment env, 
    ILoggerFactory loggerFactory)
{
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();

    app.UseApplicationInsightsRequestTelemetry();

    if (env.IsDevelopment())
    {
        app.UseBrowserLink();
        app.UseDeveloperExceptionPage();
        app.UseDatabaseErrorPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");

        try
        {
            using (var serviceScope = app.ApplicationServices
                .GetRequiredService<IServiceScopeFactory>()
                .CreateScope())
            {
                serviceScope.ServiceProvider
                        .GetService<ApplicationDbContext>()
                        .Database.Migrate();
            }
        }
        catch { }
    }

    app.UseIISPlatformHandler(options => options.AuthenticationDescriptions.Clear());

    app.UseApplicationInsightsExceptionTelemetry();
    app.UseStaticFiles();
    app.UseIdentity();

    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
    });

    app.Run((async (context) =>
    {
        await context.Response.WriteAsync("Error");
    }));
}

我的HomeController构造函数是：

public HomeController(IConfiguration configuration, IEmailSender mailService)
{
    _mailService = mailService;
    _to = configuration["emailAddress.Support"];
}

请告诉我哪里弄错了。

微软扩展。依赖注入。服务查找。服务PopulateCallSites（ServiceProvider提供程序，ISet'1 callSiteChain，ParameterInfo[]参数，Boolean throwIfCallSiteNotFound）

Answer 1

将项目从. Net Core 1. x移动到2.0时，将所有IConfigurationRoot更改为IConfiguration

Answer 2

在Core 2.0中，建议使用IConfiguration而不是IConfigurationRoot

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

public IConfiguration Configuration { get; }

从…起https://docs.microsoft.com/en-us/aspnet/core/migration/1x-to-2x/#add-配置提供程序

Answer 3

尝试将其注入为IConfigurationRoot而不是IConfiguration：

 public HomeController(IConfigurationRoot configuration
    , IEmailSender mailService)
{
    _mailService = mailService;
    _to = configuration["emailAddress.Support"];
}

在这种情况下

services.AddSingleton(provider => Configuration);

相当于

services.AddSingleton<IConfigurationRoot>(provider => Configuration);

因为类上的Configuration属性是这样声明的，注入将通过匹配它注册为的任何类型来完成。我们可以很容易地复制这一点，这可能会更清楚：

public interface IParent { }

public interface IChild : IParent { }

public class ConfigurationTester : IChild { }

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddMvc();

    IChild example = new ConfigurationTester();
    services.AddSingleton(provider => example);
}

public class HomeController : Controller
{
    public HomeController(IParent configuration)
    {
        // this will blow up
    }
}

正如stephen.vakil评论中提到的，最好将配置文件加载到一个类中，然后根据需要将该类注入到控制器中。这看起来像这样：

services.Configure<AppSettings>(Configuration.GetSection("AppSettings"));

您可以使用IOptions界面获取这些配置：

public HomeController(IOptions<AppSettings> appSettings)