asp.net core 依赖注入实现全过程粗略剖析(1)
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常用扩展方法 注入依赖服务:
new ServiceCollection().AddSingletonIApplicationBuilder, ApplicationBuilder>
();
// AddSingleton多个重载方法 源码
public static IServiceCollection AddSingletonTService, 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 : IListServiceDescriptor>
{
}
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 FuncIServiceProvider, 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(IEnumerableServiceDescriptor>
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
源码地址:https://github.com/aspnet/DependencyInjection
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