在 .NET Core 中使用不同的构造函数参数（DI 和非 DI）注册多个 IHostedService 实例

Question

I have an environment with 4 identical devices that I have to connect to and request some parameters via TCP connection (each device with its IP address). I've implemented a class for a single device that needs some parameters (like IP address, port, polling intervals etc...)

The class implements BackgroundService interface and has a constructor like this one below:

public RemoteDevice(RemoteDeviceConfig config, ILogger<RemoteDevice> logger)

Inside the class there is an implementation of the ExecuteAsync method with a while{} loop inside, that does all the logic.

I want to build a Worker Service that handles multiple instances of that class, based on a configuration file (eg. config file with an array of devices)

In Program.cs I would do:

public static void Main(string[] args)
{
    CreateHostBuilder(args).Build().Run();
}

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .UseSystemd()
        .ConfigureServices((hostContext, services) =>
        {
            services.AddHostedService<RemoteDevice>(); //First device
            services.AddHostedService<RemoteDevice>(); //Second device
            ...
            services.AddHostedService<RemoteDevice>(); //n-th device

        });
...
//Methods to load configuration 
...

Without the RemoteDeviceConfig constructor parameter, the ILogger gets injected, but if I add it, I don't know how to inject my RemoteDeviceConfig class

What am I getting wrong?

I'm using .NET Core 3.0 with VS2019 and Worker Service Template project.

UPDATE - ACCEPTED ANSWER

I've accepted @gldraphael answer , and I would add some details about the logging part specified in the answer's comments.

Problem: use ILogger implementation in classes instantiated in main Worker class.

Solution: inject ILoggerFactory in Worker class and use it to create loggers for subclasses

DeviceMainClass and DeviceConfig are respectively a generic device manager and its configuration.

Worker.cs

List<DeviceMainClass> devices;
//Pass ILoggerFactory to worker constructor for Dependency Injection
//On worker start, instantiate all subclasses and create logger for each class
public Worker(IOptions<List<DeviceConfig>> options, ILogger<Worker> logger, ILoggerFactory loggerFactory)
{
    devices = new List<DeviceMainClass>();
    foreach(var device in _config)
    {
        devices.Add(new DeviceMainClass(_loggerFactory.CreateLogger<DeviceMainClass>(),...other parameters));
    }

    _logger = logger;
    _loggerFactory = loggerFactory;
    _config = options.Value;
}

...

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    while (!stoppingToken.IsCancellationRequested)
    {


        //***for testing purposes only, repeats every second***
        _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
        await Task.Delay(1000, stoppingToken);
    }
}

DeviceMainClass

private readonly ILogger<DeviceMainClass> _logger;

//Use
public DeviceMainClass(ILogger<DeviceMainClass> logger, ...other parameters)
{
    _logger = logger;
    ...
}

Answer 1

You wanna do something like this:

appsettings.json

{
  "Devices": [
    { "Name": "D1" },
    { "Name": "D2" },
    { "Name": "D3" },
    { "Name": "D4" }
  ]
}

CreateHostBuilder() :

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureServices((hostContext, services) =>
        {
            services.Configure<List<DeviceConfig>>(hostContext.Configuration.GetSection("Devices"));
            services.AddHostedService<Worker>();
        });

Worker:

public class Worker : BackgroundService
    {
        private readonly ILogger<Worker> _logger;
        private readonly List<DeviceConfig> config;

        public Worker(IOptions<List<DeviceConfig>> options, ILogger<Worker> logger)
        {
            config = options.Value;
            _logger = logger;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {

                foreach(var device in config)
                {
                    // TODO: Process each device here
                    _logger.LogInformation("Processing device {name}", device.Name);
                }


                await Task.Delay(1000, stoppingToken);
            }
        }
    }

---

If your current RemoteDevice class has state information, create a List<RemoteDevice> in the worker and initialize from configuration.

Answer 2

As I have faced similar problem recently - I am bumping this old question.

Consider using any mature DI container instead of default of default one. Say with Autofac it will look like:

public class Program {
    public static void Main(string[] args) {
        Host.CreateDefaultBuilder(args)
            .UseServiceProviderFactory(new AutofacServiceProviderFactory())
            .ConfigureContainer<ContainerBuilder>(builder => { builder.RegisterType<DeviceMainClass>(); })
            .ConfigureServices(services => { services.AddHostedService<Worker>(); })
            //...
            .Build()
            .Run();
    }
}

public class DeviceConfig {
    //...
}

public class DeviceMainClass {
    private readonly ILogger<DeviceMainClass> _logger;
    private readonly DeviceConfig _deviceConfig;

    public DeviceMainClass(ILogger<DeviceMainClass> logger, DeviceConfig deviceConfig) {
        _logger = logger;
        _deviceConfig = deviceConfig;
    }
}

public class Worker : BackgroundService {
    List<DeviceMainClass> devices;

    private readonly ILogger<Worker> _logger;
    private readonly List<DeviceConfig> _config;

    public Worker(IOptions<List<DeviceConfig>> options, Func<DeviceConfig, DeviceMainClass> deviceFactory, ILogger<Worker> logger) {
        _logger = logger;
        _config = options.Value;
        devices = new List<DeviceMainClass>();
        foreach (var deviceConfig in _config) {
            //autofac automatically adds appropriate logger when calling DeviceMainClass constructor                
            devices.Add(deviceFactory(deviceConfig)); 
        }

    }
}

Check for more details here and here .