ASP.Net Core MVC 依赖注入不起作用 [英] ASP.Net Core MVC Dependency Injection not working

问题描述

我正在尝试将接口注入到我的 HomeController 中，但出现此错误:

I am trying to inject a interface into to my HomeController and I am getting this error:

InvalidOperationException:尝试激活时无法解析Microsoft.Extensions.Configuration.IConfiguration"类型的服务

InvalidOperationException: Unable to resolve service for type 'Microsoft.Extensions.Configuration.IConfiguration' while attempting to activate

我的Startup类如下:

My Startup class is as follows:

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:

and my HomeController constructor is:

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

请告诉我我错在哪里.

Microsoft.Extensions.DependencyInjection.ServiceLookup.Service.PopulateCallSites(ServiceProvider provider, ISet`1 callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)

Microsoft.Extensions.DependencyInjection.ServiceLookup.Service.PopulateCallSites(ServiceProvider provider, ISet`1 callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)

推荐答案

尝试将其作为 IConfigurationRoot 而不是 IConfiguration 注入:

Try injecting it as an IConfigurationRoot instead of IConfiguration:

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

在这种情况下，该行

services.AddSingleton(provider => Configuration);

等价于

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:

because the Configuration property on the class is declared as such, and injection will be done by matching whatever type it was registered as. We can replicate this pretty easily, which might make it clearer:

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
    }
}

不过

正如评论中提到的 stephen.vakil，最好将您的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.看起来像这样:

However

As stephen.vakil mentioned in the comments, it would be better to load your configuration file into a class, and then inject that class into controllers as needed. That would look something like this:

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

您可以使用 IOptions 界面获取这些配置:

You can grab these configurations with the IOptions interface:

public HomeController(IOptions<AppSettings> appSettings)

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