Program.cs

using Microsoft.Extensions.DependencyInjection;

namespace DependencyInjectionTest
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, World!");

            var services = new ServiceCollection();

            services.AddScoped<SendMessageManager>();
            services.AddScoped<IMessageSenderService, SmsMessageSenderService>();
            services.AddScoped<IBancoDeDados, MySqlBancoDados>();

            var container = services.BuildServiceProvider();

            var manager = container.GetService<SendMessageManager>();
            manager.SendMessage(new Message() { Content = "asdasd" });
        }
    }

  
    public class SendMessageManager
    {
        private readonly IMessageSenderService messageSenderService;
        private readonly IBancoDeDados bancoDeDados;

        public SendMessageManager(IMessageSenderService messageSenderService, IBancoDeDados bancoDeDados)
        {
            this.messageSenderService = messageSenderService;
            this.bancoDeDados = bancoDeDados;
        }
        
        //post
        public void SendMessage(Message message)
        {
            messageSenderService.Send(message);
            bancoDeDados.SalvaLogNoBanco();
        }
    }

    public interface IMessageSenderService
    {
        bool Send(Message message);
    }

    public class WhatsAppMessageSenderService : IMessageSenderService
    {
        public bool Send(Message message)
        {
            Console.WriteLine("enviou por whatsapp");
            return true;
        }
    }

    public class SmsMessageSenderService : IMessageSenderService
    {
        public bool Send(Message message)
        {
            Console.WriteLine("enviou por sms");
            return true;
        }
    }

    public class Message
    {
        public string Sender { get; set; }
        public string Recipient { get; set; }
        public string Content { get; set; }

    }

    public interface IBancoDeDados
    {
        void SalvaLogNoBanco();
    }

    public class MySqlBancoDados : IBancoDeDados
    {
        public void SalvaLogNoBanco()
        {
            Console.WriteLine("Salvou no banco de dados");
        }
    }
}