将IConfiguration注入.NET Core3.0中的Program.cs (控制台应用)

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;

class Program
{
    static void Main(string[] args)
    {
        var host = new HostBuilder()
            .ConfigureAppConfiguration((hostContext, configBuilder) =>
            {
                configBuilder.AddJsonFile("appsettings.json", optional: true);
            })
            .ConfigureServices((hostContext, services) =>
            {
                services.AddSingleton<IConfiguration>(hostContext.Configuration);
                services.AddTransient<MyService>();
            })
            .Build();

        var myService = ActivatorUtilities.CreateInstance<MyService>(host.Services);
        myService.DoSomething();

        host.Run();
    }
}

class MyService
{
    private readonly IConfiguration _configuration;

    public MyService(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public void DoSomething()
    {
        var value = _configuration["MyKey"];
        Console.WriteLine(value);
    }
}