Console Application DI Pattern

A guide for implementing dependency injection using GenericHost in .NET Console Application.

1. Required NuGet Package

<ItemGroup>
  <PackageReference Include="Microsoft.Extensions.Hosting" Version="9.0.*" />
</ItemGroup>

2. Basic Implementation

2.1 Program.cs

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var host = Host.CreateDefaultBuilder(args)
    .ConfigureServices((context, services) =>
    {
        services.AddSingleton<IMyService, MyService>();
        services.AddSingleton<App>();
    })
    .Build();

var app = host.Services.GetRequiredService<App>();
await app.RunAsync();

2.2 App.cs

namespace MyApp;

public sealed class App(IMyService myService)
{
    private readonly IMyService _myService = myService;

    public async Task RunAsync()
    {
        await _myService.DoWorkAsync();
    }
}

3. Service Lifetime

| Lifetime | Description | Use When | |----------|-------------|----------| | Singleton | Single instance for entire app | Stateless services | | Scoped | Single instance per request | DbContext | | Transient | New instance per injection | Lightweight services |

4. Configuration Integration

var host = Host.CreateDefaultBuilder(args)
    .ConfigureAppConfiguration((context, config) =>
    {
        config.AddJsonFile("appsettings.json", optional: true);
    })
    .ConfigureServices((context, services) =>
    {
        services.Configure<AppSettings>(
            context.Configuration.GetSection("AppSettings"));
        services.AddSingleton<App>();
    })
    .Build();

5. Logging Integration

public sealed class App(ILogger<App> logger)
{
    public Task RunAsync()
    {
        logger.LogInformation("Application started");
        return Task.CompletedTask;
    }
}

6. Important Notes

⚠️ Avoid Service Locator Pattern

// ❌ Bad example
public sealed class BadService(IServiceProvider provider)
{
    public void DoWork()
    {
        var service = provider.GetRequiredService<IMyService>();
    }
}

// ✅ Good example
public sealed class GoodService(IMyService myService)
{
    public void DoWork() { }
}

⚠️ Captive Dependency

• Singleton should not inject Scoped/Transient dependencies

7. References

• .NET Generic Host