[Tools]IOC控制反轉 & DI依賴注入 & Autofac

IOC(Inversion of Control)控制反轉是物件導向程式設計中的一種設計原則，可以用來減低電腦程式碼之間的耦合度。
依賴注入(Dependency Injection)是最常使用的方式。

IOC(Inversion of Control)

以下用程式碼做簡單的範例說明:

public class ObjectA
{
    private ObjectB obj = new ObjectB();

    public void FindSomething()
    {
        obj.FindB();
    }
}

public class ObjectB
{
    public void FindB()
    {
        Console.WriteLine("ObjectB FindB");
    }
}

ObjectA 使用 ObjectB 的方法去完成一項工作，在 ObjectA 要 new 一個 ObjectB 起來
所以在建立 ObjectA 時，也會把 ObjectB 建立起來
換句話說，現在沒有 ObjectB 就沒有 ObjectA ， ObjectA 相依於 ObjectB

如果 ObjectB 需要替換，就必須修改宣告、new 的類型也要修改，可能呼叫的方法也要改，如下:

public class ObjectA
{
    private ObjectC obj = new ObjectC();

    public void FindSomething()
    {
        obj.FindC();
    }
}

public class ObjectC
{
    public void FindC()
    {
        Console.WriteLine("ObjectC FindC");
    }
}

比較好的設計方式是相依於介面

public interface IObject
{
    void Find();
}

public class ObjectA
{
    private IObject obj = new ObjectB();

    public void FindSomething()
    {
        obj.Find();
    }
}

public class ObjectB : IObject
{
    public void Find()
    {
        Console.WriteLine("ObjectB Find");
    }
}

public class ObjectC : IObject
{
    public void Find()
    {
        Console.WriteLine("ObjectC Find");
    }
}

DI(Dependency Injection)

這樣在抽換物件時，只需要變更建立類型即可，還可以搭配 DI 讓程式碼更靈活
常見的注入方式有三種:

建構子注入，這是最常見的方式

public class ObjectA
{
    private IObject obj;

    public void ObjectA(IObject obj)
    {
        this.obj = obj;
    }

    public void FindSomething()
    {
        obj.Find();
    }
}

屬性注入，適合相依物件需要與外部互動

public class ObjectA
{
    private IObject obj;

    public IObject Obj
    {
        get
        {
            return this.obj;
        }
        set
        {
            this.obj = value;
        }
    }

    public void FindSomething()
    {
        if (this.obj == null)
        {
            throw new ArgumentNullException("obj", "obj is null");
        }
        obj.Find();
    }
}

參數注入

public class ObjectA
{
    public void FindSomething(IObject obj)
    {
        if (obj == null)
        {
            throw new ArgumentNullException("obj", "obj is null");
        }
        obj.Find();
    }
}

IOC容器Tool-Autofac

透過NuGet安裝Autofac套件

Autofac套件

依照專案是MVC 或是 WebApi 去安裝整合套件

整合套件

在App_Start資料夾下新增一個AutofacConfig

namespace WebApi.App_Start
{
    using System.Reflection;
    using System.Web.Mvc;
    using Autofac;
    using Autofac.Integration.Mvc;
    using Autofac.Integration.WebApi;

    public static class AutofacConfig
    {
        public static IContainer Container;

        public static void RegisterContainer()
        {
            var builder = new ContainerBuilder();
            builder.RegisterApiControllers(Assembly.GetExecutingAssembly());

            builder.RegisterAssemblyTypes(Assembly.Load("WebApi.Domain"), Assembly.Load("WebApi.Persistent"))
                .WithParameter("connectionString", ConfigHelper.MasterDB)
                .Where(t => t.Namespace == "WebApi.Persistent.SQL" || t.Namespace == "WebApi.Domain.Repository")
                .As(t => t.GetInterfaces().FirstOrDefault(i => i.Name == $"I{t.Name}"))
                .SingleInstance();

            builder.RegisterAssemblyTypes(Assembly.Load("WebApi.Domain"), Assembly.Load("WebApi.Persistent"))
                .WithParameter("connectionString", ConfigHelper.MongoDBConnectionString)
                .WithParameter("dbName", ConfigHelper.MongoDBName)
                .Where(t => t.Namespace == "WebApi.Persistent.Mongo" || t.Namespace == "WebApi.Domain.Repository")
                .As(t => t.GetInterfaces().FirstOrDefault(i => i.Name == $"I{t.Name}"))
                .SingleInstance();

            Container = builder.Build();

            var config = GlobalConfiguration.Configuration;
            config.DependencyResolver = new AutofacWebApiDependencyResolver(Container);
            DependencyResolver.SetResolver(new AutofacDependencyResolver(Container));
        }
    }
}

在Global的Application_Start啟用Autofac

protected void Application_Start()
{
    GlobalConfiguration.Configure(WebApiConfig.Register);
    AutofacConfig.RegisterContainer();
}

使用方式

建構子注入

public class TestController : ApiController
{
    private IMemberInfoRepository memberInfoRepo;
    public MemberController(IMemberInfoRepository memberInfoRepo)
    {
        this.memberInfoRepo = memberInfoRepo;
    }

    public Results GetMemberInfo()
    {
        var findResult = this.memberInfoRepo.GetMemberInfo();
    }
}

using

public class TestController : ApiController
{
    public Results GetMemberInfo()
    {
        using (var scope = App_Start.AutofacConfig.Container.BeginLifetimeScope())
        {
            var memberInfoRepo = scope.Resolve<IMemberInfoRepository>();
            var findResult = memberInfoRepo.GetMemberInfo();
        }
    }
}