使用构造函数注入时，依赖关系只能在对象您正在创建的实际上是通过 依赖项注入本身创建的。因此，使依赖注入在您的 Worker 中起作用的关键是实际上也通过依赖注入容器解析 Worker 。

When using constructor injection, dependencies will only be resolved when the object you are creating is actually created through dependency injection itself. So the key to make dependency injection work within your Worker is to actually resolve Worker through the dependency injection container as well.

这实际上很简单：

var services = new ServiceCollection()
    .AddLogging(b => b.AddConsole())
    .AddDbContext<UnderstandingDIContext>(options =>
        options.UseSqlite(builder.GetConnectionString("DefaultConnection")));

// register `Worker` in the service collection
services.AddTransient<Worker>();

// build the service provider
var serviceProvider = services.BuildServiceProvider();

// resolve a `Worker` from the service provider
var worker = serviceProvider.GetService<Worker>();

var logger = serviceProvider.GetService<ILogger<Program>>();
logger.LogInformation("Starting Application");

worker.Run();

logger.LogInformation("Closing Application");

此外，由于您使用的数据库上下文已注册为作用域默认情况下为em>依赖项，我建议您也创建一个服务范围，或者在注册时更改数据库上下文的生存期。

In addition, since you are using a database context which gets registered as a scoped dependency by default, I would recommend you to create a service scope as well—or alternatively change the lifetime of the database context when you register it.

var serviceProvider = services.BuildServiceProvider();

using (var scope = serviceProvider.CreateScope())
{
    var worker = serviceProvider.GetService<Worker>();
    worker.Run();
}

请注意，我还做了一个显式方法 Run 对您的worker的使用，这样您就无需在构造函数中使用逻辑。

Note that I also made an explicit method Run on your worker, so that you don’t have the logic within the constructor.

public class Worker
{
    private readonly ILogger<Worker> _logger = logger;
    private readonly IConfiguration _configuration = configuration;
    private readonly UnderstandingDIContext _dbContext = dbContext;

    public Worker(ILogger<Worker> logger, IConfiguration configuration, UnderstandingDIContext dbContext)
    {
        _logger = logger;
        _configuration = configuration;
        _dbContext = dbContext;
    }

    public void Run()
    {
        _logger.LogInformation("Inside Worker Class");
        var settings = new Settings()
        {
            Secret1 = configuration["Settings:Secret1"],
            Secret2 = configuration["Settings:Secret2"]
        };

        _logger.LogInformation($"Secret 1 is '{settings.Secret1}'");
        _logger.LogInformation($"Secret 2 is '{settings.Secret2}'");

        _dbContext.Add(new UnderstandingDIModel()
        {
            Message = "Adding a message to the database."
        });
        _dbContext.SaveChanges();
    }
}