ASP.NET Core 2+中的ILogger和DependencyInjection

Question

我注意到Startup.cs中的ConfigureServices中沒有明確的ILogger注冊。

第一個問題： ILogger如何被注入到例如控制器中。

第二個問題：如何配置ILogger以注入中間件？

Answer 1

日志記錄是HostBuilder.Build過程的一部分

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();

要將ILogger注入控制器，只需將其作為依賴項包含在構造函數中

private readonly ILogger logger;

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

//...

並且框架將在激活時將其注入控制器。

參考依賴注入ASP.NET Core中的控制器

與控制器一樣，Middleware vai構造函數注入也可以這樣做，

或者直接進入每個請求依賴項的Invoke方法

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

像任何其他注入的服務

參考ASP.NET核心中間件