Dependency Injection in ASP.NET Core

Transient – A new instance of the service is created each time it is requested. It can be used for stateless and light weight services.

可以理解为每次都要创建，主要针对状态无关、轻量级的服务。

Scoped – A single instance is created once per request.

每次HttpRequest就创建一次，HttpRequest以内就不用创建了；下一次HttpRequest的话要重新创建。

Singleton – Created only once the first time they are requested.

应用程序内只创建一次。

玩过Autofac的同学发现这个其实和Autofac是一样的。

Ref:http://www.c-sharpcorner.com/article/dependency-injection-in-Asp-Net-core/

Startup的ConfigureServices主要用于依赖注入的配置

public void ConfigureServices(IServiceCollection services)
        {
            // Add framework services.
            services.AddDbContext<ApplicationDbContext>(options =>
                options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

            services.AddIdentity<ApplicationUser, IdentityRole>()
                .AddEntityFrameworkStores<ApplicationDbContext>()
                .AddDefaultTokenProviders();

            services.AddMvc();

            // Add application services.
            services.AddTransient<IEmailSender, AuthMessageSender>();
            services.AddTransient<ISmsSender, AuthMessageSender>();

            services.AddTransient<FruitServices>();
        }