Console Application DI Pattern

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