DI 1

Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;

namespace DiExamples
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddSingleton<IPhotoService, PhotoService>();
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.Run(async (context) =>
            {
                var photoService = context.RequestServices.GetRequiredService<IPhotoService>();
                await context.Response.WriteAsync(photoService.Upload());
            });
        }
    }

    public interface IPhotoService
    {
        string Upload();
    }

    public class PhotoService : IPhotoService
    {
        private IHostingEnvironment _env;
        public PhotoService(IHostingEnvironment env)
        {
            _env = env;
        }
        public string Upload()
        {
            // Do some work
            return "Upload Done";
        }
    }
}