How to pass parameters for BackgroundService?

Question

I read about ASP.net core 2.2 and I found reference about generic host.

I tried to create console app with backgroundService under example: https://github.com/aspnet/AspNetCore.Docs/tree/master/aspnetcore/fundamentals/host/generic-host/samples/

var param = Console.ReadLine();

var host = new HostBuilder().ConfigureServices((hostContext, services) =>
{
   services.AddHostedService<MyCustomSerivce>();
}

The problem is how can be passed argument from command line (in my case 'param'), that will specified internal logic in particular background service.

Answer 1

For resolving service, you need to register the parameters into service collection.

1. Service for storing the parameter

   public class CommandLineArgs
   {
       public string Args { get; set; }
   }
   

2. Register the parameter

   public class Program
   {
       public static async Task Main(string[] args)
       {
           var param = Console.ReadLine();
   
           var host = new HostBuilder()
               .ConfigureHostConfiguration(configHost =>
               {
                   configHost.SetBasePath(Directory.GetCurrentDirectory());
                   configHost.AddJsonFile("hostsettings.json", optional: true);
                   configHost.AddEnvironmentVariables(prefix: "PREFIX_");
                   configHost.AddCommandLine(args);
               })
               .ConfigureAppConfiguration((hostContext, configApp) =>
               {
                   configApp.AddJsonFile("appsettings.json", optional: true);
                   configApp.AddJsonFile(
                       $"appsettings.{hostContext.HostingEnvironment.EnvironmentName}.json", 
                       optional: true);
                   configApp.AddEnvironmentVariables(prefix: "PREFIX_");
                   configApp.AddCommandLine(args);
               })
               .ConfigureServices((hostContext, services) =>
               {
                   services.AddSingleton(new CommandLineArgs { Args = param });
                   services.AddHostedService<LifetimeEventsHostedService>();
                   services.AddHostedService<TimedHostedService>();
               })
               .ConfigureLogging((hostContext, configLogging) =>
               {
                   configLogging.AddConsole();
                   configLogging.AddDebug();
               })
               .UseConsoleLifetime()
               .Build();
   
           await host.RunAsync();
       }
   }
   

3. Resolve service

   internal class TimedHostedService : IHostedService, IDisposable
   {
       private readonly ILogger _logger;
       private Timer _timer;
       private readonly IConfiguration _configuration;
       private readonly CommandLineArgs _commandLineArgs;
       public TimedHostedService(ILogger<TimedHostedService> logger
           , IConfiguration configuration
           , CommandLineArgs commandLineArgs)
       {
           _logger = logger;
           _configuration = configuration;
           _commandLineArgs = commandLineArgs;
       }       
   }