C# ConsoleApp injection startup?

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I have a simple C# .NET Core 5 Console Application that I need to add dependency injection (Microsoft.Extensions.DependencyInjection) to. I know how to do this if it suppose to start a micro service but what If I want to just run it as a regular Console Application with DI?

I got this code :

static void Main(string[] args)
{
    var serviceName =
        System.Reflection.Assembly.GetExecutingAssembly().GetName().Name;

    var configurationBuilder = new ConfigurationBuilder()
        .AddJsonFile("appsettings.json").Build();
    var appSettings = configurationBuilder.Get<AppSettings>();

        Log.Information("{@serviceName} test starting up.", serviceName);
        Host.CreateDefaultBuilder(args)
            .UseMyAppMQ(context => context.UseSettings(appSettings.MQSettings))
            .UseSerilog((hostingContext, loggerConfiguration) => loggerConfiguration.ReadFrom.Configuration(hostingContext.Configuration))
            .ConfigureServices((hostContext, services) =>
            {
                services
                    .Configure<MQSettings>(configurationBuilder.GetSection("MQSettings"))
                    .AddTransient<ITestController>(s => new TestController());
            })
            .Build().Run();

        Log.Information("{@serviceName} test closing down.", serviceName);
}

I need a entry point where I can run my underlaying class run method, but how?

Regards

dependency-injection c#
1 Answers

You need to implement IHostedService interface (or extend BackgroundService base class) and register it with services.AddHostedService<YourServiceClass>() or builder.Services.AddHostedService<YourServiceClass>(), if using .NET 6 minimal API as described in official docs. In this case IHostedService.StartAsync will be your entry point.

However, it does seem very inefficient, if all you need is just a simple console app with DI. As @Panagiotis Kanavos suggests you can build the host without running it, because then you can use it as a wrapper around DI container and resolve any registered service. In this case the entry point for your code is the next line after you've built your host, where you can resolve any registered dependency with

var host = Host.CreateDefaultBuilder(args)
   ...
   .Build();
host.Services.GetService<YouService>()

But it is still an inefficient solution for just a console app, because you only need DI container, but not the entire host. Just use any third-party DI framework (like Autofac, Ninject or any other) instead of Microsoft.Extensions.DependencyInjection. Their setup is usually quite minimalistic and you will get just DI container with you services without anything else. You can still use configuration package and loggers, just register them in your container similarly to how you've done it before with UseXxxx methods.

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