Application startup

Startup class

The Startup class (which is named Startup just by convention) is where:

• The request handling pipeline is defined (Configure method).

• [OPTIONAL] Configured services required by the app (ConfigureServices method).

public class Startup
{
    // Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddTransient<ISomeInterface, SomeClass>();
    
        services.AddMvc()
            .SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

        services.AddDbContext<MovieContext>(options =>
                options.UseSqlServer(Configuration.GetConnectionString("MovieDb")));
    }

    // Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app)
    {
        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseMvc();
    }
}

Dependency injection works even for Startup class!

A common use of dependency injection into the Startup class is to inject:

• IHostingEnvironment to configure services by environment.

• IConfiguration to read configuration.

• ILoggerFactory to create a logger in Startup.ConfigureServices

Building app's host

The Startup class is specified to the app when the app's host is built. The Startup class is usually specified by calling the WebHostBuilderExtensions.UseStartup<TStartup> method on the host builder:

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

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>();
}

You can build webhost even without Startup class!

To configure services and the request processing pipeline without using a Startup class, call ConfigureServices and Configure convenience methods on the host builder.

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

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .ConfigureServices(services =>
            {
                // ┌( ͝° ͜ʖ͡°)=ε/̵͇̿̿/’̿’̿ ̿    (̿▀̿ ̿Ĺ̯̿̿▀̿ ̿)̄
            })
            .Configure(app =>
            {
                // (╥﹏╥)
            });
}