ASP.NET Core 2+ 中的 ILogger 和 DependencyInjection

Question

我注意到ConfigureServices 中的Startup.cs 中没有明确的ILogger 注册。

第一个问题：ILogger 如何注入到例如控制器。

第二个问题：如何配置ILogger 注入中间件？

Answer 1

日志记录作为HostBuilder.Build 进程的一部分添加

private void CreateServiceProvider()
{
    var services = new ServiceCollection();
    services.AddSingleton(_hostingEnvironment);
    services.AddSingleton(_hostBuilderContext);
    services.AddSingleton(_appConfiguration);
    services.AddSingleton<IApplicationLifetime, ApplicationLifetime>();
    services.AddSingleton<IHostLifetime, ConsoleLifetime>();
    services.AddSingleton<IHost, Host>();
    services.AddOptions();
    services.AddLogging();//<--HERE

    //...

WebHostBuilder.BuildCommonServices

    private IServiceCollection BuildCommonServices(out AggregateException hostingStartupErrors)
    {

        //... code removed for brevity

        var services = new ServiceCollection();
        services.AddSingleton(_options);
        services.AddSingleton<IHostingEnvironment>(_hostingEnvironment);
        services.AddSingleton<Extensions.Hosting.IHostingEnvironment>(_hostingEnvironment);
        services.AddSingleton(_context);

        var builder = new ConfigurationBuilder()
            .SetBasePath(_hostingEnvironment.ContentRootPath)
            .AddConfiguration(_config);

        _configureAppConfigurationBuilder?.Invoke(_context, builder);

        var configuration = builder.Build();
        services.AddSingleton<IConfiguration>(configuration);
        _context.Configuration = configuration;

        var listener = new DiagnosticListener("Microsoft.AspNetCore");
        services.AddSingleton<DiagnosticListener>(listener);
        services.AddSingleton<DiagnosticSource>(listener);

        services.AddTransient<IApplicationBuilderFactory, ApplicationBuilderFactory>();
        services.AddTransient<IHttpContextFactory, HttpContextFactory>();
        services.AddScoped<IMiddlewareFactory, MiddlewareFactory>();
        services.AddOptions();
        services.AddLogging();

要将ILogger 注入控制器，只需将其作为依赖项包含在构造函数中

private readonly ILogger logger;

public MyController(ILogger<MyController> logger) {
    this.logger = logger;
}

//...

并且框架会在它被激活时将其注入到控制器中。

参考Dependency injection into controllers in ASP.NET Core

中间件vai构造函数注入也可以像控制器一样，

或直接进入Invoke方法为per-request dependencies

public Task Invoke(HttpContext context, ILogger<MyMiddleware> logger) {
    //...
}

像任何其他注入服务一样

参考ASP.NET Core Middleware