Asp.net core 学习笔记 ( DI 依赖注入 )-白红宇

Asp.net core 学习笔记 ( DI 依赖注入 )

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发布时间：2019-06-25

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更新 2019-05-06

用泛型来传 class, 这样比较方便扩展

services.AddEmail
     
      ();services.AddEmail
      
       ();

AddEmail

public static class ServiceCollectionExtensions{    public static IServiceCollection AddEmail
     
      (        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
     
      (Configuration.GetSection("business"));    services.Configure
      
       (Configuration.GetSection("email"));    services.AddEmail();    // Razor template     services.AddSingleton
       
        ();    services.AddSingleton
        
         ();    // Entity     services.AddScoped(_ => new DB(Configuration.GetConnectionString("DefaultConnection")));    // hangfire    services.AddHangfire(config =>            config.UseSqlServerStorage(Configuration.GetConnectionString("DefaultConnection")));    // MVC    services.Configure
         
          (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
     
       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
     
      ();            services.AddSingleton
      
       ();            services.AddScoped
       
        ();            return services;        }    }    public class EmailService    {        public EmailService()        {        }        public string name { get; set; } = "dada";    }}