asp.net core 依赖注入实现全过程粗略剖析（1）

转载请注明出处： https://home.cnblogs.com/u/zhiyong-ITNote/

常用扩展方法注入依赖服务：

new ServiceCollection().AddSingleton<IApplicationBuilder, ApplicationBuilder>();

// AddSingleton多个重载方法源码

public static IServiceCollection AddSingleton<TService, TImplementation>(this IServiceCollection services)

where TService : class

where TImplementation : class, TService

{

if (services == null)

{

throw new ArgumentNullException(nameof(services));

}

return services.AddSingleton(typeof(TService), typeof(TImplementation));

}

// Singleton模式 最终的调用

public static IServiceCollection AddSingleton(

this IServiceCollection services,

Type serviceType,

Type implementationType)

{

if (services == null)

{

throw new ArgumentNullException(nameof(services));

}

if (serviceType == null)

{

throw new ArgumentNullException(nameof(serviceType));

}

if (implementationType == null)

{

throw new ArgumentNullException(nameof(implementationType));

}

return Add(services, serviceType, implementationType, ServiceLifetime.Singleton);

}

// 所有的Addxxx 最终都是调用Add方法，将ServiceDescriptor添加到IServiceCollection中：

private static IServiceCollection Add(

IServiceCollection collection,

Type serviceType,

Type implementationType,

ServiceLifetime lifetime)

{

var descriptor = new ServiceDescriptor(serviceType, implementationType, lifetime);

collection.Add(descriptor);

return collection;

}

// IServiceCollection源码：

public interface IServiceCollection : IList<ServiceDescriptor>

{}

如上，我们一般在ConfigureService中使用Addxxx将服务注入框架的过程。大概做个总结，其实就是屌用IServiceCollection的Addxxx 扩展方法，随后调用Add方法，初始化一个ServiceDescriptor，参数是我们注入的接口和类，还有就是生命周期。随后添加到IServiceCollection中，根据该接口的定义就是一个ServiceDescriptor的集合。

我们看看ServiceDescriptor的源码：

public ServiceDescriptor(

 Type serviceType,

 object instance)

 : this(serviceType, ServiceLifetime.Singleton)

{

 if (serviceType == null)

 {

 throw new ArgumentNullException(nameof(serviceType));

 } 

 if (instance == null)

 {

 throw new ArgumentNullException(nameof(instance));

 } 

 ImplementationInstance = instance;

}

该类就是初始化并获取如下属性：

/// <inheritdoc />

public ServiceLifetime Lifetime { get; }

/// <inheritdoc />

public Type ServiceType { get; }

/// <inheritdoc />

public Type ImplementationType { get; }

/// <inheritdoc />

public object ImplementationInstance { get; }

/// <inheritdoc />

public Func<IServiceProvider, object> ImplementationFactory { get; }

到此，我们的服务注入到asp.net core框架中就完事了，那么服务的实例化呢？

首先我们理下思路，IServiceProvider接口对应的实现是ServiceProvider,这个类就是实例化了IServiceProvider接口，而IServiceProvider接口只有一个方法：

public object GetService(Type serviceType);

该方法就是获取注入的服务。但是ServiceProvider类不单单是获取注入的服务，服务的实例化还是在该类中实现的，我们看下：

public sealed class ServiceProvider : IServiceProvider, IDisposable, IServiceProviderEngineCallback

{

private readonly IServiceProviderEngine _engine;

private readonly CallSiteValidator _callSiteValidator;

internal ServiceProvider(IEnumerable<ServiceDescriptor> serviceDescriptors, ServiceProviderOptions options)

{

IServiceProviderEngineCallback callback = null;

if (options.ValidateScopes)

{

callback = this;

_callSiteValidator = new CallSiteValidator();

}

switch (options.Mode)

{

case ServiceProviderMode.Dynamic:

_engine = new DynamicServiceProviderEngine(serviceDescriptors, callback);

break;

case ServiceProviderMode.Runtime:

_engine = new RuntimeServiceProviderEngine(serviceDescriptors, callback);

break;

#if IL_EMIT

case ServiceProviderMode.ILEmit:

_engine = new ILEmitServiceProviderEngine(serviceDescriptors, callback);

break;

#endif

case ServiceProviderMode.Expressions:

_engine = new ExpressionsServiceProviderEngine(serviceDescriptors, callback);

break;

default:

throw new NotSupportedException(nameof(options.Mode));

}

}

/// <summary>

/// Gets the service object of the specified type.

/// </summary>

/// <param name="serviceType"></param>

/// <returns></returns>

public object GetService(Type serviceType) => _engine.GetService(serviceType);

/// <inheritdoc />

public void Dispose() => _engine.Dispose();

void IServiceProviderEngineCallback.OnCreate(IServiceCallSite callSite)

{

_callSiteValidator.ValidateCallSite(callSite);

}

void IServiceProviderEngineCallback.OnResolve(Type serviceType, IServiceScope scope)

{

_callSiteValidator.ValidateResolution(serviceType, scope, _engine.RootScope);

}

}

可以看到该类的构造函数中就是实例化服务的过程了。很直白的可以看出我们常见的几种方法来实例化类：反射，Emit，表达式树等...

目前也算是交代清楚了相关的类。那么框架具体是如何来实例化的呢？整个的流程是怎么样的。篇2再叙

转载请注明出处： https://home.cnblogs.com/u/zhiyong-ITNote/

源码地址：https://github.com/aspnet/DependencyInjection

巴特西

asp.net core 依赖注入实现全过程粗略剖析（1）

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