码迷,mamicode.com
首页 > Web开发 > 详细

ASP.NET Core中的依赖注入(5):ServicePrvider实现揭秘【补充漏掉的细节】

时间:2016-04-17 00:36:00      阅读:876      评论:0      收藏:0      [点我收藏+]

标签:

到目前为止,我们定义的ServiceProvider已经实现了基本的服务提供和回收功能,但是依然漏掉了一些必需的细节特性。这些特性包括如何针对IServiceProvider接口提供一个ServiceProvider对象,何创建ServiceScope,以及如何提供一个服务实例的集合。

一、提供一个ServiceProvider对象

我们知道当将服务类型指定为IServiceProvider接口并调用ServiceProvider的GetService方法是,ServiceProvider对象本身将会作为服务实例返回,这个特性可以利用一个自定义的Service来实现。如下面的代码片段所示,我们定义的这个ServiceProviderService既是一个Service,又是一个ServiceCallSite。它默认采用生命周期管理模式为Scoped,在Invoke和Build方法中,它直接将当前ServiceProvider作为提供的服务实例。在初始化ServiceTable的时候,我们额外添加一个针对ServiceProviderService的ServideEntry。

   1: internal class ServiceProviderService : IService, IServiceCallSite
   2: {
   3:     public ServiceLifetime Lifetime => ServiceLifetime.Scoped;
   4:     public IService Next { get; set; }
   5:  
   6:     public Expression Build(Expression provider)
   7:     {
   8:         return provider;
   9:     }
  10:  
  11:     public IServiceCallSite CreateCallSite(ServiceProvider provider, ISet<Type> callSiteChain)
  12:     {
  13:         return this;
  14:     }
  15:  
  16:     public object Invoke(ServiceProvider provider)
  17:     {
  18:         return provider;
  19:     }
  20: }
  21:  
  22: internal class ServiceTable
  23: {
  24:     public ServiceTable(IServiceCollection services)
  25:     {
  26:         //解析ServiceCollection并添加相应ServiceEntry
  27:         this.ServieEntries[typeof(IServiceProvider)] = new ServiceEntry(new ServiceProviderService());
  28:     }
  29: }


二、创建ServiceScope

创建ServiceScope的目的在于创建作为当前ServiceProvider儿子的另一个ServiceProvider,新创建的ServiceProvider不仅与原来的ServiceProvider具有相同的根,同时共享所有的服务注册信息。利用这个新的ServiceProvider来代替现有的ServiceProvider,其主要的目的还是使我们能够及时地回收提供的服务实例。ServiceScope是通过它的工厂ServiceScopeFactory来创建的,所以先创建了如下一个ServiceScopeFactory类和对应的ServiceScope,它们的定义与我们在前面一节介绍的完全一致。

   1: internal class ServiceScope : IServiceScope
   2: {
   3:     public IServiceProvider ServiceProvider { get; private set; }
   4:  
   5:     public ServiceScope(ServiceProvider serviceProvider)
   6:     {
   7:         this.ServiceProvider = serviceProvider;
   8:     }
   9:  
  10:     public void Dispose()
  11:     {
  12:         (this.ServiceProvider as IDisposable)?.Dispose();
  13:     }
  14: }
  15:  
  16: internal class ServiceScopeFactory : IServiceScopeFactory
  17: {
  18:     public ServiceProvider ServiceProvider { get; private set; }
  19:  
  20:     public ServiceScopeFactory(ServiceProvider serviceProvider)
  21:     {
  22:         this.ServiceProvider = serviceProvider;
  23:     }
  24:  
  25:     public IServiceScope CreateScope()
  26:     {
  27:         return new ServiceScope(this.ServiceProvider);
  28:     }
  29: }
  30:  
  31: internal class ServiceProvider : IServiceProvider, IDisposable
  32: {
  33:     
  34:     public ServiceProvider(ServiceProvider parent)
  35:     {
  36:         this.Root = parent.Root;
  37:         this.ServiceTable = parent.ServiceTable;
  38:     }
  39: }

为了让ServiceProvider的GetService方法在服务类型指定为IServiceScopeFactory接口的时候能够自动返回上面我们定义的ServiceScopeFactory对象,我们依然和上面一样创建了一个自定义的Service,并将其命名为ServiceScopeFactoryService。与ServiceProviderService一样,ServiceScopeFactoryService同时也是一个ServiceCallSite,在Build和Invoke方法中它会返回一个ServiceScopeFactory对象。为了让这个它能够生效,我们依然在ServiceTable初始化的时自动添加一个相应的ServiceEntry。

   1: internal class ServiceScopeFactoryService : IService, IServiceCallSite
   2: {
   3:     public ServiceLifetime Lifetime=> ServiceLifetime.Scoped;
   4:     public IService Next { get; set; }
   5:  
   6:     public IServiceCallSite CreateCallSite(ServiceProvider provider, ISet<Type> callSiteChain)
   7:     {
   8:         return this;
   9:     }
  10:  
  11:     public Expression Build(Expression provider)
  12:     {
  13:         return Expression.New(typeof(ServiceScopeFactory).GetConstructors().Single(), provider);
  14:     }
  15:  
  16:     public object Invoke(ServiceProvider provider)
  17:     {
  18:         return new ServiceScopeFactory(provider);
  19:     }
  20: }
  21:  
  22: internal class ServiceTable
  23: {
  24:     public ServiceTable(IServiceCollection services)
  25:     {
  26:         //解析ServiceCollection并添加相应ServiceEntry
  27:         this.ServieEntries[typeof(IServiceProvider)] =  new ServiceEntry(new ServiceProviderService());
  28:         this.ServieEntries[typeof(IServiceScopeFactory)] = new ServiceEntry(new ServiceScopeFactoryService());
  29:     }
  30: }


三、提供一组服务的集合

到目前为止,我们自定义的ServiceProvider尚不具备原生ServiceProvider的一项特性,那就是当调用GetService方法时将服务类型指定为IEnumerable<T>或者直接调用扩展方法GetServices时,得到的是一个服务实例的集合。这个特性可以通过一个自定义的ServiceCallSite来完成,我们将其命名为EnumerableCallSite。

   1: internal class EnumerableCallSite : IServiceCallSite
   2: {
   3:     public Type ElementType { get; private set; }
   4:     public IServiceCallSite[] ServiceCallSites { get; private set; }
   5:  
   6:     public EnumerableCallSite(Type elementType, IServiceCallSite[] serviceCallSites)
   7:     {
   8:         this.ElementType = elementType;
   9:         this.ServiceCallSites = serviceCallSites;
  10:     }
  11:  
  12:     public Expression Build(Expression provider)
  13:     {
  14:         return Expression.NewArrayInit(this.ElementType, this.ServiceCallSites.Select(
  15:             it => Expression.Convert(it.Build(provider), this.ElementType)));
  16:     }
  17:  
  18:     public object Invoke(ServiceProvider provider)
  19:     {
  20:         var array = Array.CreateInstance(this.ElementType, this.ServiceCallSites.Length);
  21:         for (var index = 0; index < this.ServiceCallSites.Length; index++)
  22:         {
  23:             array.SetValue(this.ServiceCallSites[index].Invoke(provider), index);
  24:         }
  25:         return array;
  26:     }
  27: }

如上面的代码片段所示,EnumerableCallSite具有两个两个只读属性(ElementType和ServiceCallSites),前者表示返回的服务集合的元素类型,后者则返回一组用于提供集合元素的ServiceCallSite。在Invoke和Build方法中,我们只需要根据元素类型创建一个数组,并利用这组ServiceCallSite创建所有的元素即可。这个EnumerableCallSite最终按照如下的方式应用到ServiceProvider的GetServiceCallSite方法中。

   1: internal class ServiceProvider : IServiceProvider, IDisposable
   2: { 
   3:     public IServiceCallSite GetServiceCallSite(Type serviceType, ISet<Type> callSiteChain)
   4:     {
   5:         try
   6:         {
   7:             if (callSiteChain.Contains(serviceType))
   8:             {
   9:                 throw new InvalidOperationException(string.Format("A circular dependency was detected for the service of type ‘{0}‘",serviceType.FullName);
  10:             }
  11:             callSiteChain.Add(serviceType);
  12:             ServiceEntry serviceEntry;
  13:             if (this.ServiceTable.ServieEntries.TryGetValue(serviceType, out serviceEntry))
  14:             {
  15:                 return serviceEntry.Last.CreateCallSite(this, callSiteChain);
  16:             }
  17:  
  18:             if (serviceType.IsGenericType && serviceType.GetGenericTypeDefinition()== typeof(IEnumerable<>))
  19:             {
  20:                 Type elementType = serviceType.GetGenericArguments()[0];
  21:                 IServiceCallSite[] serviceCallSites = this.ServiceTable.ServieEntries.TryGetValue(elementType, out serviceEntry)
  22:                     ? serviceEntry.All.Select(it => it.CreateCallSite(this, callSiteChain)).ToArray()
  23:                     : new IServiceCallSite[0];
  24:                 return new EnumerableCallSite(elementType, serviceCallSites);
  25:             }
  26:  
  27:             return null;
  28:         }
  29:         finally
  30:         {
  31:             callSiteChain.Remove(serviceType);
  32:         }
  33:     }
  34:     //其他成员
  35: }

 

ASP.NET Core中的依赖注入(1):控制反转(IoC)
ASP.NET Core中的依赖注入(2):依赖注入(DI)
ASP.NET Core中的依赖注入(3):服务注册与提取
ASP.NET Core中的依赖注入(4):构造函数的选择与生命周期管理
ASP.NET Core中的依赖注入(5):ServicePrvider实现揭秘【总体设计】
ASP.NET Core中的依赖注入(5):ServicePrvider实现揭秘【解读ServiceCallSite】
ASP.NET Core中的依赖注入(5):ServicePrvider实现揭秘【补充漏掉的细节】

ASP.NET Core中的依赖注入(5):ServicePrvider实现揭秘【补充漏掉的细节】

标签:

原文地址:http://www.cnblogs.com/artech/p/asp-net-core-di-service-provider-3.html

(0)
(0)
   
举报
评论 一句话评论(0
登录后才能评论!
© 2014 mamicode.com 版权所有  联系我们:gaon5@hotmail.com
迷上了代码!