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.NET - Program Class and Main Method in a Nutshell

Tutorial built with .NET 5.0

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The Main() method is the entry point for a .NET application, when an app is started it searches for the Main() method to begin execution. The method can be located anywhere in a project but is typically placed in the Program class.

A .NET web app is run within a host which handles app startup, lifetime management, web server configuration and more. A host is created and launched by calling Build().Run() on a host builder (an instance of the IHostBuilder interface). A generic host builder with pre-configured defaults is created with the CreateDefaultBuilder() convenience method provided by the static Host class (Microsoft.Extensions.Hosting.Host).

The ConfigureWebHostDefaults() extension method configures the host builder for hosting a web app including setting Kestrel as the web server, adding host filtering middleware and enabling IIS integration. For more info on the default host builder settings see https://docs.microsoft.com/aspnet/core/fundamentals/host/generic-host#default-builder-settings.

The x.UseStartup<Startup>() method specifies which startup class to use when building a host for the web app.

A minimal Program class with Main method

This is an example of a minimal .NET Program class with a Main() method that creates and configures a web host using the methods described above. The code is from a tutorial I posted recently on how to create a minimal .NET API by hand from scratch, for more info see .NET 5.0 - Bare Bones API Tutorial.

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;

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

        public static IHostBuilder CreateHostBuilder(string[] args)
        {
            return Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(x => x.UseStartup<Startup>());
        }
    }
}

 


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