Asp.net core 学习笔记 ( DI 依赖注入 )

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";
}
}