ASP.NET Core MVC内置服务的使用

ASP.NET Core中的依赖注入可以说是无处不在，其通过创建一个ServiceCollection对象并将服务注册信息以ServiceDescriptor对象的形式添加在其中，其次针对ServiceCollection对象创建对应的ServiceProvider，通过ServiceProvider提供我们需要的服务实例。

这里通过IServiceCollection来查看一下 其默认注册了哪些服务。

• 1、使用asp.net core mvc默认模板，命令行创建项目

dotnet new mvc -o projectname

Microsoft.Extensions.DependencyInjection中提供很多IServiceCollection的扩展方法来添加服务注册。如：

/// <summary>
/// Adds MVC services to the specified <see cref="IServiceCollection" />.
/// </summary>
/// <param name="services">The <see cref="IServiceCollection" /> to add services to.</param>
/// <returns>An <see cref="IMvcBuilder"/> that can be used to further configure the MVC services.</returns>
public static IMvcBuilder AddMvc(this IServiceCollection services)
{
if (services == null)
{
throw new ArgumentNullException(nameof(services));
}

services.AddControllersWithViews();
return services.AddRazorPages();
}

public static IMvcBuilder AddControllers(this IServiceCollection services)
{
if (services == null)
{
throw new ArgumentNullException(nameof(services));
}

var builder = AddControllersCore(services);
return new MvcBuilder(builder.Services, builder.PartManager);
}

• 2、在Startup.cs中 将IServiceCollection中注册的服务输出到日志

private IServiceCollection _services;

public Startup(IConfiguration configuration)
{
Configuration = configuration;
}

public IConfiguration Configuration { get; }

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.Configure<CookiePolicyOptions>(options =>
{
// This lambda determines whether user consent for non-essential cookies is needed for a given request.
options.CheckConsentNeeded = context => true;
options.MinimumSameSitePolicy = SameSiteMode.None;
});

services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

_services = services;

}
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
var _logger = loggerFactory.CreateLogger("Services");
_logger.LogInformation($"Total Services Registered: {_services.Count}");
foreach (var service in _services)
{
_logger.LogInformation($"Service: {service.ServiceType.FullName}\n      Lifetime: {service.Lifetime}\n      Instance: {service.ImplementationType?.FullName}");
}
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseCookiePolicy();

app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}");
});
}

• 3、我们能够直接获取这些服务的实例来使用，也可以使用第三方容器如：AspectCore、Autofac

例：使用AspectCore

public class AspectCoreContainer
{
private static IServiceResolver resolver { get; set; }
public static IServiceProvider BuildServiceProvider(IServiceCollection services, Action<IAspectConfiguration> configure = null)
{
if(services==null)throw new ArgumentNullException(nameof(services));
services.ConfigureDynamicProxy(configure);
services.AddAspectCoreContainer();
return resolver = services.ToServiceContainer().Build();
}

public static T Resolve<T>()
{
if (resolver == null)
throw new ArgumentNullException(nameof(resolver), "调用此方法时必须先调用BuildServiceProvider！");
return resolver.Resolve<T>();
}
public static List<T> ResolveServices<T>()
{
if (resolver == null)
throw new ArgumentNullException(nameof(resolver), "调用此方法时必须先调用BuildServiceProvider！");
return resolver.GetServices<T>().ToList();
}
}

调用Resolve拿到实例

var razorViewEngine = AspectCoreContainer.Resolve<IRazorViewEngine>();
var compositeViewEngine = AspectCoreContainer.Resolve<ICompositeViewEngine>();
var tempDataProvider = AspectCoreContainer.Resolve<ITempDataProvider>();
var serviceProvider = AspectCoreContainer.Resolve<IServiceProvider>();
var options = AspectCoreContainer.Resolve<IOptions>();