ASP.NET Core中IOC容器的实现原理

DotNetCore实战

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 ·

2020-09-20 12:26

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本章将和大家分享ASP.NET Core中IOC容器的实现原理。

首先我们需要了解什么是IOC,为什么要使用IOC容器?

一、依赖

类A用到了类B,我们就说类A依赖类B。

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using System;

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

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

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上面的示例中,类Test就依赖了MyDependency类。

二、依赖倒置原则(Dependence Inversion Principle)

依赖倒置原则:高层模块不应该依赖于低层模块,二者都应该依赖于抽象。应该依赖于抽象,而不是依赖细节。

什么是高层模块?这里的使用者Test类就称为高层模块。什么是低层模块?被使用者MyDependency类就称为低层模块。上面的示例中我们的高层模块就依赖于我们的低层模块。

那么这样子有什么不好呢?

  1、面向对象语言开发,就是类与类之间进行交互,如果高层直接依赖低层的细节,细节是多变的,那么低层的变化就导致上层的变化;

  2、如果层数多了,低层的修改会直接水波效应传递到最上层,一点细微的改动都会导致整个系统从下往上的修改。

因此,上例按照依赖倒置原则修改如下:

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using System;

namespace MyIOCDI
{
public class Test
{
public void Show()
{
IDepenency myDependency
= new MyDependency(); //左边抽象右边细节
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();
}
}

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三、IOC控制反转

控制反转是一种思想,所谓“控制反转”就是反转获得依赖对象的过程。

上面示例经过改造后虽然遵循了“依赖倒置原则”,但是违背了“开放封闭原则”,因为如果有一天想要修改变量myDependency为YourDependency类的实例,则需要修改Test类。

因此,我们需要反转这种创建对象的过程:

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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();
}
}

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上例中,将 _myDependency 的创建过程“反转”给了调用者。

四、依赖注入(Dependency Injection)

依赖注入是一种在类及其依赖对象之间实现控制反转(IOC)思想的技术。

所谓依赖注入,就是由IOC容器在运行期间,动态地将某种依赖关系注入到对象之中。

依赖注入就是能做到构造某个对象时,将依赖的对象自动初始化并注入 。

IOC是目标是效果,需要DI依赖注入的手段。

三种注入方式:构造函数注入--属性注入--方法注入(按时间顺序)。

构造函数注入用的最多,默认找参数最多的构造函数,可以不用特性,可以去掉对容器的依赖。

五、IOC容器的实现原理

IOC容器的实现原理:

  1、启动时保存注册信息。

  2、在构造某个对象时,根据注册信息使用反射加特性,将依赖的对象自动初始化并注入。

  3、对对象进行生命周期管理或者进行AOP扩展等。

下面我们重点来看下如何创建一个简易的IOC容器(当然,实际使用的IOC容器要比这复杂的多)。

首先来看下项目的目录结构:

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此处IOC容器中用到的自定义特性如下所示:

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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
///
/// 构造函数注入特性
///

[AttributeUsage(AttributeTargets.Constructor)]
public class ConstructorInjectionAttribute : Attribute
{

}
}

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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
///
/// 方法注入特性
///

[AttributeUsage(AttributeTargets.Method)]
public class MethodInjectionAttribute : Attribute
{

}
}

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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
///
/// 常量
///

[AttributeUsage(AttributeTargets.Parameter)]
public class ParameterConstantAttribute : Attribute
{

}
}

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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
///
/// 简称(别名)
///

[AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property)]
public class ParameterShortNameAttribute : Attribute
{
public string ShortName { get; private set; }
public ParameterShortNameAttribute(string shortName)
{
this.ShortName = shortName;
}
}
}

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using System;

namespace TianYaSharpCore.IOCDI.CustomAttribute
{
///
/// 属性注入特性
///

[AttributeUsage(AttributeTargets.Property)]
public class PropertyInjectionAttribute : Attribute
{

}
}

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创建一个简易的IOC容器,如下所示:

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using System;

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

///
/// 生命周期
///

public LifetimeType Lifetime { get; set; }

///
/// 仅限单例
///

public object SingletonInstance { get; set; }
}

///
/// 生命周期
///

public enum LifetimeType
{
Transient,
//瞬时
Singleton,
Scope,
//作用域
PerThread //线程单例
//外部可释放单例
}
}

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using System;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
///
/// IOC容器接口
///

public interface ITianYaIOCContainer
{
void Register(string shortName = null, object[] paraList = null, LifetimeType lifetimeType = LifetimeType.Transient)
where TTo : TFrom;
TFrom Resolve
(string shortName = null);
ITianYaIOCContainer CreateChildContainer();
}
}

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

using TianYaSharpCore.IOCDI.CustomAttribute;

namespace TianYaSharpCore.IOCDI.CustomContainer
{
///
/// IOC容器
///

public class TianYaIOCContainer : ITianYaIOCContainer
{
#region 字段或者属性

///
/// 保存注册信息
///

private Dictionary<string, IOCContainerRegistModel> _tianYaContainerDictionary = new Dictionary<string, IOCContainerRegistModel>();

///
/// 保存常量的值
///

private Dictionary<string, object[]> _tianYaContainerValueDictionary = new Dictionary<string, object[]>();

///
/// 作用域单例的对象
///

private Dictionary<string, object> _tianYaContainerScopeDictionary = new Dictionary<string, object>();

#endregion 字段或者属性

#region 构造函数

///
/// 无参构造行数
///

public TianYaIOCContainer()
{

}

///
/// 主要在创建子容器的时候使用
///

private TianYaIOCContainer(Dictionary<string, IOCContainerRegistModel> tianYaContainerDictionary,
Dictionary
<string, object[]> tianYaContainerValueDictionary, Dictionary<string, object> tianYaContainerScopeDictionary)
{
this._tianYaContainerDictionary = tianYaContainerDictionary;
this._tianYaContainerValueDictionary = tianYaContainerValueDictionary;
this._tianYaContainerScopeDictionary = tianYaContainerScopeDictionary;
}

#endregion 构造函数

///
/// 创建子容器
///

public ITianYaIOCContainer CreateChildContainer()
{
return new TianYaIOCContainer(this._tianYaContainerDictionary, this._tianYaContainerValueDictionary,
new Dictionary<string, object>()); //没有注册关系,最好能初始化进去
}

///
/// 获取键
///

private string GetKey(string fullName, string shortName) => $"{fullName}___{shortName}";

///
/// 加个参数区分生命周期--而且注册关系得保存生命周期
///

/// 要添加的服务的类型
/// 要使用的实现的类型
/// 简称(别名)(主要用于解决单接口多实现)
/// 常量参数
/// 生命周期
public void Register(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);
}
}

///
/// 获取对象
///

public TFrom Resolve(string shortName = null)
{
return (TFrom)this.ResolveObject(typeof(TFrom), shortName);
}

///
/// 递归--可以完成不限层级的对象创建
///

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 选择合适的构造函数

ConstructorInfo ctor
= null;
//标记特性
ctor = type.GetConstructors().FirstOrDefault(c => c.IsDefined(typeof(ConstructorInjectionAttribute), true));
if (ctor == null)
{
//参数个数最多
ctor = type.GetConstructors().OrderByDescending(c => c.GetParameters().Length).First();
}
//ctor = type.GetConstructors()[0]; //直接第一个

#endregion 选择合适的构造函数

#region 准备构造函数的参数

List
<object> paraList = new List<object>();
object[] paraConstant = this._tianYaContainerValueDictionary.ContainsKey(key) ? this._tianYaContainerValueDictionary[key] : null; //常量找出来
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; //获取参数的类型
string paraShortName = this.GetShortName(para);
object paraInstance = this.ResolveObject(paraType, paraShortName);
paraList.Add(paraInstance);
}
}

#endregion 准备构造函数的参数

object oInstance = null;
oInstance
= Activator.CreateInstance(type, paraList.ToArray()); //创建对象,完成构造函数的注入

#region 属性注入

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 属性注入

#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;//获取参数的类型 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扩展
return oInstance;
}

///
/// 获取简称(别名)
///

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;
}
}
}
}

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至此,我们就创建完了一个简易的IOC容器。

下面我们来添加一些用于测试的接口,如下所示:

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using System;

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

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using System;

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

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using System;

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

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using System;

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

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接口对应的实现,如下所示:

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using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
public class TestServiceA : ITestServiceA
{
public TestServiceA()
{
Console.WriteLine($
"{this.GetType().Name}被构造。。。");
}

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

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using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
public class TestServiceB : ITestServiceB
{
public TestServiceB()
{
Console.WriteLine($
"{this.GetType().Name}被构造。。。");
}

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

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using System;

using MyIOCDI.IService;

namespace MyIOCDI.Service
{
public class TestServiceC : ITestServiceC
{
public TestServiceC()
{
Console.WriteLine($
"{this.GetType().Name}被构造。。。");
}

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

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using System;

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

namespace MyIOCDI.Service
{
public class TestServiceD : ITestServiceD
{
///
/// 属性注入
///

[PropertyInjection]
public ITestServiceA TestServiceA { get; set; }

///
/// 带有别名的属性注入
///

[ParameterShortName("ServiceB")]
[PropertyInjection]
public ITestServiceB TestServiceB { get; set; }

public TestServiceD()
{
Console.WriteLine($
"{this.GetType().Name}被构造。。。");
}

#region 构造函数注入

private readonly ITestServiceA _testServiceA;
private readonly ITestServiceB _testServiceB;
[ConstructorInjection]
//优先选择带有构造函数注入特性的
public TestServiceD(ITestServiceA testServiceA, [ParameterConstant] string sValue, ITestServiceB testServiceB, [ParameterConstant] int iValue)
{
Console.WriteLine($
"{this.GetType().Name}--{sValue}--{iValue}被构造。。。");
_testServiceA
= testServiceA;
_testServiceB
= testServiceB;
}

#endregion 构造函数注入

#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");
}
}
}

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最后来看下IOC容器的使用及其运行结果:

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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();
{
//注册
container.Register(); //将ITestServiceA注册到TestServiceA
container.Register();
container.Register
(shortName: "ServiceB");
container.Register
();
container.Register
(paraList: new object[] { "浪子天涯", 666 }, lifetimeType: LifetimeType.Singleton);

ITestServiceD d1
= container.Resolve(); //创建对象交给IOC容器
ITestServiceD d2 = container.Resolve();
d1.Show();
Console.WriteLine($
"object.ReferenceEquals(d1, d2) = {object.ReferenceEquals(d1, d2)}");
}

Console.ReadKey();
}
}
}

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运行结果如下:

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生命周期为作用域的,其实就是子容器单例,如下所示:

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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();
//{
// //注册
// container.Register(); //将ITestServiceA注册到TestServiceA
// container.Register();
// container.Register(shortName: "ServiceB");
// container.Register();
// container.Register(paraList: new object[] { "浪子天涯", 666 }, lifetimeType: LifetimeType.Singleton);

// ITestServiceD d1 = container.Resolve(); //创建对象交给IOC容器
// ITestServiceD d2 = container.Resolve();
// d1.Show();
// Console.WriteLine($"object.ReferenceEquals(d1, d2) = {object.ReferenceEquals(d1, d2)}");
//}

{
//生命周期:作用域
//就是Http请求时,一个请求处理过程中,创建都是同一个实例;不同的请求处理过程中,就是不同的实例;
//得区分请求,Http请求---Asp.NetCore内置Kestrel,初始化一个容器实例;然后每次来一个Http请求,就clone一个,
//或者叫创建子容器(包含注册关系),然后一个请求就一个子容器实例,那么就可以做到请求单例了(其实就是子容器单例)
//主要可以去做DbContext Repository
container.Register(lifetimeType: LifetimeType.Scope);
ITestServiceA a1
= container.Resolve();
ITestServiceA a2
= container.Resolve();

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

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

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

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();
}
}
}

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运行结果如下:

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至此本文就全部介绍完了,如果觉得对您有所启发请记得点个赞哦!!!

 

Demo源码:

链接:https://pan.baidu.com/s/15xpmWbEDbkm7evpr4iIZNg
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