Asp.net core 学习笔记 ( DI 依赖注入 )

更新 2020-01-11

动态创建 class 并且可以使用 DI, 这样反射样就可以了

var instance = ActivatorUtilities.CreateInstance<AbcService>(serviceProvider);

更新 2019-05-06

用泛型来传 class, 这样比较方便扩展

services.AddEmail<EmailService>();

services.AddEmail<NewEmailService>();

AddEmail

public static class ServiceCollectionExtensions

{

    public static IServiceCollection AddEmail<TEmailService>(

        this IServiceCollection services

    )

    where TEmailService : IEmailService

    {

        services.AddScoped(typeof(IEmailService), typeof(TEmailService));

        return services;

    }

}

public interface IEmailService

{

    string GetValue();

}

public class EmailService : IEmailService

{

    public string GetValue()

    {

        return "email v1";

    }

}

public class NewEmailService : IEmailService

{

    public string GetValue()

    {

        return "email v2";

    }

}

比起 Angular 的依赖注入, core 的相对简单许多, 容易明白

所有 provider 都在 startup 里配置.

public void ConfigureServices(IServiceCollection services)

{

    services.Configure<Business>(Configuration.GetSection("business"));

    services.Configure<Configuration.Email>(Configuration.GetSection("email"));

    services.AddEmail();

    // Razor template

    services.AddSingleton<ICompositeViewEngine, CompositeViewEngine>();

    services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();

    // Entity

    services.AddScoped(_ => new DB(Configuration.GetConnectionString("DefaultConnection")));

    // hangfire

    services.AddHangfire(config =>

            config.UseSqlServerStorage(Configuration.GetConnectionString("DefaultConnection")));

    // MVC

    services.Configure<RazorViewEngineOptions>(options =>

    {

        options.ViewLocationExpanders.Add(new FeatureLocationExpander());

    });

    services.AddMvc();

}

controller 就通过 constructor 来注入就可以了.

private readonly DB db;

private ICompositeViewEngine CompositeViewEngine { get; set; }

private ActionContext ActionContext { get; set; }

private IServiceProvider ServiceProvider { get; set; }

private ITempDataProvider TempDataProvider { get; set; }

private Configuration.Email EmailConfig { get; set; }

public DebugController(

    DB db,

    ICompositeViewEngine compositeViewEngine,

    IActionContextAccessor actionContextAccessor,

    IServiceProvider serviceProvider,

    ITempDataProvider tempDataProvider,

    IOptionsSnapshot<Configuration.Email> emailOptionsAccessor

)

{

    CompositeViewEngine = compositeViewEngine;

    ActionContext = actionContextAccessor.ActionContext;

    ServiceProvider = serviceProvider;

    TempDataProvider = tempDataProvider;

    EmailConfig = emailOptionsAccessor.Value;

    this.db = db;

}

provider 有 3 个级别

AddSingleton

AddScoped

AddTransient

单列是说整个 App 用一个实例

Scope 一个 request 一个实例

transient 则是每一个注入一个实例

一个模块一般上会提供好多 Service

那么要让 startup 干净一些的话，我们可以包装起来

就好像这样 services.AddEmail();

做法是开一个扩展方法

namespace Project.Email

{

    public static class ServiceCollectionExtensions

    {

        public static IServiceCollection AddEmail(

            this IServiceCollection services)

        {

            services.AddSingleton<ICompositeViewEngine, CompositeViewEngine>();

            services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();

            services.AddScoped<EmailService, EmailService>();

            return services;

        }

    }

    public class EmailService

    {

        public EmailService()

        {

        }

        public string name { get; set; } = "dada";

    }

}

巴特西

Asp.net core 学习笔记 ( DI 依赖注入 )

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