ASP.NET Core中IOC容器的實作原理-有解無憂

本章將和大家分享ASP.NET Core中IOC容器的實作原理，

首先我們需要了解什么是IOC，為什么要使用IOC容器？

一、依賴

類A用到了類B，我們就說類A依賴類B，

using System;

namespace MyIOCDI
{
    public class Test
    {
        public void Show()
        {
            MyDependency myDependency = new MyDependency(); //全是細節
            myDependency.Show();
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public class MyDependency
    {
        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }
}

上面的示例中，類Test就依賴了MyDependency類，

二、依賴倒置原則（Dependence Inversion Principle）

依賴倒置原則：高層模塊不應該依賴于低層模塊，二者都應該依賴于抽象，應該依賴于抽象，而不是依賴細節，

什么是高層模塊？這里的使用者Test類就稱為高層模塊，什么是低層模塊？被使用者MyDependency類就稱為低層模塊，上面的示例中我們的高層模塊就依賴于我們的低層模塊，

那么這樣子有什么不好呢？

　　1、面向物件語言開發，就是類與類之間進行互動，如果高層直接依賴低層的細節，細節是多變的，那么低層的變化就導致上層的變化；

　　2、如果層數多了，低層的修改會直接水波效應傳遞到最上層，一點細微的改動都會導致整個系統從下往上的修改，

因此，上例按照依賴倒置原則修改如下：

using System;

namespace MyIOCDI
{
    public class Test
    {
        public void Show()
        {
            IDepenency myDependency = new MyDependency(); //左邊抽象右邊細節
            myDependency.Show();
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public class MyDependency : IDepenency
    {
        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public interface IDepenency
    {
        void Show();
    }
}

三、IOC控制反轉

控制反轉是一種思想，所謂“控制反轉”就是反轉獲得依賴物件的程序，

上面示例經過改造后雖然遵循了“依賴倒置原則”，但是違背了“開放封閉原則”，因為如果有一天想要修改myDependency為YourDependency類的實體，則需要修改Test類，

因此，我們需要反轉這種創建物件的程序：

using System;

namespace MyIOCDI
{
    public class Test
    {
        private readonly IDepenency _myDependency;
        public Test(IDepenency myDependency)
        {
            this._myDependency = myDependency;
        }

        public void Show()
        {
            _myDependency.Show();
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public class MyDependency : IDepenency
    {
        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().FullName}");
        }
    }

    public interface IDepenency
    {
        void Show();
    }
}

上例中，將 _myDependency 的創建程序“反轉”給了呼叫者，

四、依賴注入（Dependency Injection）

所謂依賴注入，就是由IOC容器在運行期間，動態地將某種依賴關系注入到物件之中，

依賴注入就是能做到構造某個物件時，將依賴的物件自動初始化并注入，

IOC是目標是效果，需要DI依賴注入的手段，

三種注入方式：建構式注入--屬性注入--方法注入（按時間順序），

建構式注入用的最多，默認找引數最多的建構式，可以不用特性，可以去掉對容器的依賴，

五、IOC容器的實作原理

IOC容器的實作原理：

　　1、啟動時保存注冊資訊，

　　2、在構造某個物件時，使用反射加特性，將依賴的物件自動初始化并注入，

　　3、對物件進行生命周期管理或者進行AOP擴展等，

下面我們重點來看下模擬實作IOC容器的代碼：

首先來看下專案的目錄結構：

此處IOC容器中用到的自定義特性如下所示：

using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 建構式注入特性
    /// </summary>
    [AttributeUsage(AttributeTargets.Constructor)]
    public class ConstructorInjectionAttribute : Attribute
    {

    }
}

using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 方法注入特性
    /// </summary>
    [AttributeUsage(AttributeTargets.Method)]
    public class MethodInjectionAttribute : Attribute
    {

    }
}

using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 常量
    /// </summary>
    [AttributeUsage(AttributeTargets.Parameter)]
    public class ParameterConstantAttribute : Attribute
    {

    }
}

using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 簡稱（別名）
    /// </summary>
    [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property)]
    public class ParameterShortNameAttribute : Attribute
    {
        public string ShortName { get; private set; }
        public ParameterShortNameAttribute(string shortName)
        {
            this.ShortName = shortName;
        }
    }
}

using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
    /// <summary>
    /// 屬性注入特性
    /// </summary>
    [AttributeUsage(AttributeTargets.Property)]
    public class PropertyInjectionAttribute : Attribute
    {

    }
}

IOC容器實作如下所示：

using System;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
    public class IOCContainerRegistModel
    {
        public Type TargetType { get; set; }

        /// <summary>
        /// 生命周期
        /// </summary>
        public LifetimeType Lifetime { get; set; }

        /// <summary>
        /// 僅限單例
        /// </summary>
        public object SingletonInstance { get; set; }
    }

    /// <summary>
    /// 生命周期
    /// </summary>
    public enum LifetimeType
    {
        Transient, //瞬時
        Singleton,
        Scope, //作用域
        PerThread //執行緒單例
        //外部可釋放單例
    }
}

using System;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
    /// <summary>
    /// IOC容器介面
    /// </summary>
    public interface ITianYaIOCContainer
    {
        void Register<TFrom, TTo>(string shortName = null, object[] paraList = null, LifetimeType lifetimeType = LifetimeType.Transient)
            where TTo : TFrom;
        TFrom Resolve<TFrom>(string shortName = null);
        ITianYaIOCContainer CreateChildContainer();
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

using TianYaSharpCore.IOCDI.CustomAttribute;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
    /// <summary>
    /// IOC容器
    /// </summary>
    public class TianYaIOCContainer : ITianYaIOCContainer
    {
        #region 欄位或者屬性

        /// <summary>
        /// 保存注冊資訊
        /// </summary>
        private Dictionary<string, IOCContainerRegistModel> _tianYaContainerDictionary = new Dictionary<string, IOCContainerRegistModel>();

        /// <summary>
        /// 保存常量的值
        /// </summary>
        private Dictionary<string, object[]> _tianYaContainerValueDictionary = new Dictionary<string, object[]>();

        /// <summary>
        /// 作用域單例的物件
        /// </summary>
        private Dictionary<string, object> _tianYaContainerScopeDictionary = new Dictionary<string, object>();

        #endregion 欄位或者屬性

        #region 建構式

        /// <summary>
        /// 無參構造行數
        /// </summary>
        public TianYaIOCContainer()
        {

        }

        /// <summary>
        /// 主要在創建子容器的時候使用
        /// </summary>
        private TianYaIOCContainer(Dictionary<string, IOCContainerRegistModel> tianYaContainerDictionary,
            Dictionary<string, object[]> tianYaContainerValueDictionary, Dictionary<string, object> tianYaContainerScopeDictionary)
        {
            this._tianYaContainerDictionary = tianYaContainerDictionary;
            this._tianYaContainerValueDictionary = tianYaContainerValueDictionary;
            this._tianYaContainerScopeDictionary = tianYaContainerScopeDictionary;
        }

        #endregion 建構式

        /// <summary>
        /// 創建子容器
        /// </summary>
        public ITianYaIOCContainer CreateChildContainer()
        {
            return new TianYaIOCContainer(this._tianYaContainerDictionary, this._tianYaContainerValueDictionary,
                new Dictionary<string, object>()); //沒有注冊關系，最好能初始化進去
        }

        /// <summary>
        /// 獲取鍵
        /// </summary>
        private string GetKey(string fullName, string shortName) => $"{fullName}___{shortName}";

        /// <summary>
        /// 加個引數區分生命周期--而且注冊關系得保存生命周期
        /// </summary>
        /// <typeparam name="TFrom">要添加的服務的型別</typeparam>
        /// <typeparam name="TTo">要使用的實作的型別</typeparam>
        /// <param name="shortName">簡稱（別名）（主要用于解決單介面多實作）</param>
        /// <param name="paraList">常量引數</param>
        /// <param name="lifetimeType">生命周期</param>
        public void Register<TFrom, TTo>(string shortName = null, object[] paraList = null, LifetimeType lifetimeType = LifetimeType.Transient)
            where TTo : TFrom
        {
            this._tianYaContainerDictionary.Add(this.GetKey(typeof(TFrom).FullName, shortName), new IOCContainerRegistModel()
            {
                Lifetime = lifetimeType,
                TargetType = typeof(TTo)
            });

            if (paraList != null && paraList.Length > 0)
            {
                this._tianYaContainerValueDictionary.Add(this.GetKey(typeof(TFrom).FullName, shortName), paraList);
            }
        }

        /// <summary>
        /// 獲取物件
        /// </summary>
        public TFrom Resolve<TFrom>(string shortName = null)
        {
            return (TFrom)this.ResolveObject(typeof(TFrom), shortName);
        }

        /// <summary>
        /// 遞回--可以完成不限層級的物件創建
        /// </summary>
        private object ResolveObject(Type abstractType, string shortName = null)
        {
            string key = this.GetKey(abstractType.FullName, shortName);
            var model = this._tianYaContainerDictionary[key];

            #region 生命周期

            switch (model.Lifetime)
            {
                case LifetimeType.Transient:
                    Console.WriteLine("Transient Do Nothing Before");
                    break;
                case LifetimeType.Singleton:
                    if (model.SingletonInstance == null)
                    {
                        break;
                    }
                    else
                    {
                        return model.SingletonInstance;
                    }
                case LifetimeType.Scope:
                    if (this._tianYaContainerScopeDictionary.ContainsKey(key))
                    {
                        return this._tianYaContainerScopeDictionary[key];
                    }
                    else
                    {
                        break;
                    }
                default:
                    break;
            }

            #endregion 生命周期

            Type type = model.TargetType;

            #region 選擇合適的建構式

            ConstructorInfo ctor = null;
            //標記特性
            ctor = type.GetConstructors().FirstOrDefault(c => c.IsDefined(typeof(ConstructorInjectionAttribute), true));
            if (ctor == null)
            {
                //引數個數最多
                ctor = type.GetConstructors().OrderByDescending(c => c.GetParameters().Length).First();
            }
            //ctor = type.GetConstructors()[0]; //直接第一個

            #endregion 選擇合適的建構式

            #region 準備建構式的引數

            List<object> paraList = new List<object>();
            object[] paraConstant = this._tianYaContainerValueDictionary.ContainsKey(key) ? this._tianYaContainerValueDictionary[key] : null; //常量找出來
            int iIndex = 0;
            foreach (var para in ctor.GetParameters())
            {
                if (para.IsDefined(typeof(ParameterConstantAttribute), true))
                {
                    paraList.Add(paraConstant[iIndex]);
                    iIndex++;
                }
                else
                {
                    Type paraType = para.ParameterType; //獲取引數的型別
                    string paraShortName = this.GetShortName(para);
                    object paraInstance = this.ResolveObject(paraType, paraShortName);
                    paraList.Add(paraInstance);
                }
            }

            #endregion 準備建構式的引數

            object oInstance = null;
            oInstance = Activator.CreateInstance(type, paraList.ToArray()); //創建物件，完成建構式的注入

            #region 屬性注入

            foreach (var prop in type.GetProperties().Where(p => p.IsDefined(typeof(PropertyInjectionAttribute), true)))
            {
                Type propType = prop.PropertyType;
                string paraShortName = this.GetShortName(prop);
                object propInstance = this.ResolveObject(propType, paraShortName);
                prop.SetValue(oInstance, propInstance);
            }

            #endregion 屬性注入

            #region 方法注入 

            foreach (var method in type.GetMethods().Where(m => m.IsDefined(typeof(MethodInjectionAttribute), true)))
            {
                List<object> paraInjectionList = new List<object>();
                foreach (var para in method.GetParameters())
                {
                    Type paraType = para.ParameterType;//獲取引數的型別 IUserDAL
                    string paraShortName = this.GetShortName(para);
                    object paraInstance = this.ResolveObject(paraType, paraShortName);
                    paraInjectionList.Add(paraInstance);
                }
                method.Invoke(oInstance, paraInjectionList.ToArray());
            }

            #endregion 方法注入

            #region 生命周期

            switch (model.Lifetime)
            {
                case LifetimeType.Transient:
                    Console.WriteLine("Transient Do Nothing After");
                    break;
                case LifetimeType.Singleton:
                    model.SingletonInstance = oInstance;
                    break;
                case LifetimeType.Scope:
                    this._tianYaContainerScopeDictionary[key] = oInstance;
                    break;
                default:
                    break;
            }

            #endregion 生命周期

            //return oInstance.AOP(abstractType); //AOP擴展
            return oInstance;
        }

        /// <summary>
        /// 獲取簡稱（別名）
        /// </summary>
        private string GetShortName(ICustomAttributeProvider provider)
        {
            if (provider.IsDefined(typeof(ParameterShortNameAttribute), true))
            {
                var attribute = (ParameterShortNameAttribute)(provider.GetCustomAttributes(typeof(ParameterShortNameAttribute), true)[0]);
                return attribute.ShortName;
            }
            else
            {
                return null;
            }
        }
    }
}

測驗用介面如下所示：

using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceA
    {
        void Show();
    }
}

using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceB
    {
        void Show();
    }
}

using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceC
    {
        void Show();
    }
}

using System;

namespace MyIOCDI.IService
{
    public interface ITestServiceD
    {
        void Show();
    }
}

測驗用介面對應的實作如下所示：

using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
    public class TestServiceA : ITestServiceA
    {
        public TestServiceA()
        {
            Console.WriteLine($"{this.GetType().Name}被構造，，，");
        }

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}

using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
    public class TestServiceB : ITestServiceB
    {
        public TestServiceB()
        {
            Console.WriteLine($"{this.GetType().Name}被構造，，，");
        }

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}

using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
    public class TestServiceC : ITestServiceC
    {
        public TestServiceC()
        {
            Console.WriteLine($"{this.GetType().Name}被構造，，，");
        }

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}

using System;

using MyIOCDI.IService;
using TianYaSharpCore.IOCDI.CustomAttribute;

namespace MyIOCDI.Service
{
    public class TestServiceD : ITestServiceD
    {
        /// <summary>
        /// 屬性注入
        /// </summary>
        [PropertyInjection]
        public ITestServiceA TestServiceA { get; set; }

        /// <summary>
        /// 帶有別名的屬性注入
        /// </summary>
        [ParameterShortName("ServiceB")]
        [PropertyInjection]
        public ITestServiceB TestServiceB { get; set; }

        public TestServiceD()
        {
            Console.WriteLine($"{this.GetType().Name}被構造，，，");
        }

        #region 建構式注入

        private readonly ITestServiceA _testServiceA;
        private readonly ITestServiceB _testServiceB;
        [ConstructorInjection] //優先選擇帶有建構式注入特性的
        public TestServiceD(ITestServiceA testServiceA, [ParameterConstant] string sValue, ITestServiceB testServiceB, [ParameterConstant] int iValue)
        {
            Console.WriteLine($"{this.GetType().Name}--{sValue}--{iValue}被構造，，，");
            _testServiceA = testServiceA;
            _testServiceB = testServiceB;
        }

        #endregion 建構式注入

        #region 方法注入

        private ITestServiceC _testServiceC;
        [MethodInjection]
        public void Init(ITestServiceC testServiceC)
        {
            _testServiceC = testServiceC;
        }

        #endregion 方法注入

        public void Show()
        {
            Console.WriteLine($"This is {this.GetType().Name} Show");
        }
    }
}

使用IOC容器如下所示：

using System;

using TianYaSharpCore.IOCDI.CustomContainer;
using MyIOCDI.IService;
using MyIOCDI.Service;

namespace MyIOCDI
{
    class Program
    {
        static void Main(string[] args)
        {
            ITianYaIOCContainer container = new TianYaIOCContainer();
            {
                //注冊
                container.Register<ITestServiceA, TestServiceA>(); //將ITestServiceA注冊到TestServiceA
                container.Register<ITestServiceB, TestServiceB>();
                container.Register<ITestServiceB, TestServiceB>(shortName: "ServiceB");
                container.Register<ITestServiceC, TestServiceC>();
                container.Register<ITestServiceD, TestServiceD>(paraList: new object[] { "浪子天涯", 666 }, lifetimeType: LifetimeType.Singleton);

                ITestServiceD d1 = container.Resolve<ITestServiceD>(); //創建物件交給IOC容器
                ITestServiceD d2 = container.Resolve<ITestServiceD>();
                d1.Show();
                Console.WriteLine($"object.ReferenceEquals(d1, d2) = {object.ReferenceEquals(d1, d2)}");
            }

            Console.ReadKey();
        }
    }
}

運行結果如下：

using System;

using TianYaSharpCore.IOCDI.CustomContainer;
using MyIOCDI.IService;
using MyIOCDI.Service;

namespace MyIOCDI
{
    class Program
    {
        static void Main(string[] args)
        {
            ITianYaIOCContainer container = new TianYaIOCContainer();
            //{
            //    //注冊
            //    container.Register<ITestServiceA, TestServiceA>(); //將ITestServiceA注冊到TestServiceA
            //    container.Register<ITestServiceB, TestServiceB>();
            //    container.Register<ITestServiceB, TestServiceB>(shortName: "ServiceB");
            //    container.Register<ITestServiceC, TestServiceC>();
            //    container.Register<ITestServiceD, TestServiceD>(paraList: new object[] { "浪子天涯", 666 }, lifetimeType: LifetimeType.Singleton);

            //    ITestServiceD d1 = container.Resolve<ITestServiceD>(); //創建物件交給IOC容器
            //    ITestServiceD d2 = container.Resolve<ITestServiceD>();
            //    d1.Show();
            //    Console.WriteLine($"object.ReferenceEquals(d1, d2) = {object.ReferenceEquals(d1, d2)}");
            //}

            {
                //生命周期：作用域
                //就是Http請求時，一個請求處理程序中，創建都是同一個實體；不同的請求處理程序中，就是不同的實體；
                //得區分請求，Http請求---Asp.NetCore內置Kestrel，初始化一個容器實體；然后每次來一個Http請求，就clone一個，
                //或者叫創建子容器(包含注冊關系)，然后一個請求就一個子容器實體，那么就可以做到請求單例了(其實就是子容器單例)
                //主要可以去做DbContext  Repository
                container.Register<ITestServiceA, TestServiceA>(lifetimeType: LifetimeType.Scope);
                ITestServiceA a1 = container.Resolve<ITestServiceA>();
                ITestServiceA a2 = container.Resolve<ITestServiceA>();

                Console.WriteLine(object.ReferenceEquals(a1, a2)); //T

                ITianYaIOCContainer container1 = container.CreateChildContainer();
                ITestServiceA a11 = container1.Resolve<ITestServiceA>();
                ITestServiceA a12 = container1.Resolve<ITestServiceA>();

                ITianYaIOCContainer container2 = container.CreateChildContainer();
                ITestServiceA a21 = container2.Resolve<ITestServiceA>();
                ITestServiceA a22 = container2.Resolve<ITestServiceA>();

                Console.WriteLine(object.ReferenceEquals(a11, a12)); //T
                Console.WriteLine(object.ReferenceEquals(a21, a22)); //T

                Console.WriteLine(object.ReferenceEquals(a11, a21)); //F
                Console.WriteLine(object.ReferenceEquals(a11, a22)); //F
                Console.WriteLine(object.ReferenceEquals(a12, a21)); //F
                Console.WriteLine(object.ReferenceEquals(a12, a22)); //F
            }

            Console.ReadKey();
        }
    }
}

運行結果如下：

至此本文就介紹完了，如果覺得對您有所啟發請記得點個贊哦！！！

Demo原始碼：

鏈接：https://pan.baidu.com/s/15xpmWbEDbkm7evpr4iIZNg 
提取碼：ckes

此文由博主精心撰寫轉載請保留此原文鏈接：https://www.cnblogs.com/xyh9039/p/13663808.html

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標籤：.NET Core

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