.Net7 源码浅析之替换默认容器的原理

以.Net中常用的IOC容器Autofac使用方法为例[源码](autofac/Examples: Example projects that consume and demonstrate Autofac IoC functionality and integration (github.com))

在ConfigureServices方法中调用AddAutofac()拓展方法

只是注入一个单例对象生命周期的IServiceProviderFactory<ContainerBuilder>接口实现

啊原来这么简单只要实现IServiceProviderFactory<ContainerBuilder>接口就能自定义容器了？

Autofac默认注入方法了解到这来接下来我们看.Net源码中关于IServiceProviderFactory<ContainerBuilder>是如何去内部运用的如何达到容器的原理

接上章从.Net7应用程序启动开始入手依次查看到

GetProviderFromFactory()源码如下,从默认容器中拿到IServiceProviderFactory<IServiceCollection>的注入实例，然后判断是否默认容器提供DefaultServiceProviderFactory,非默认容器则直接返回实际容器CreateServiceProvider(TContainerBuilder containerBuilder)方法的返回值IServiceProvider。由上一章可知.Net7中的容器获取都是基于IServiceProvider去定义的

static IServiceProvider GetProviderFromFactory(IServiceCollection collection)
{
    var provider = collection.BuildServiceProvider();
    var factory = provider.GetService<IServiceProviderFactory<IServiceCollection>>();

    if (factory != null && factory is not DefaultServiceProviderFactory)
    {
        using (provider)
        {
            return factory.CreateServiceProvider(factory.CreateBuilder(collection));
        }
    }

    return provider;
}

再来查看IServiceProviderFactory<TContainerBuilder>的接口定义，只有CreateBuilder(IServiceCollection services)和CreateServiceProvider(TContainerBuilder containerBuilder)两个方法,再结合GetProviderFromFactory()方法的内部实现发现其实就是把默认的IServiceCollection对象都通过CreateBuilder(IServiceCollection services)传入内部然后调用CreateServiceProvider(TContainerBuilder containerBuilder)返回对应的IServiceProvider实现对象

public interface IServiceProviderFactory<TContainerBuilder> where TContainerBuilder : notnull
{
    /// <summary>
    /// Creates a container builder from an <see cref="IServiceCollection"/>.
    /// </summary>
    /// <param name="services">The collection of services</param>
    /// <returns>A container builder that can be used to create an <see cref="IServiceProvider"/>.</returns>
    TContainerBuilder CreateBuilder(IServiceCollection services);

    /// <summary>
    /// Creates an <see cref="IServiceProvider"/> from the container builder.
    /// </summary>
    /// <param name="containerBuilder">The container builder</param>
    /// <returns>An <see cref="IServiceProvider"/></returns>
    IServiceProvider CreateServiceProvider(TContainerBuilder containerBuilder);
}

分析完上述代码其实替换默认容器的原理我们大概已经明白接下来把整个步骤重新梳理一下

概况

1.源码Service中默认IServiceProviderFactory<ContainerBuilder>的实现为DefaultServiceProviderFactory

2.注入的IServiceProviderFactory<ContainerBuilder>的对应实现替换默认的DefaultServiceProviderFactory

3.IServiceProviderFactory的CreateServiceProvider方法返回对应的自定义的IServiceProvider对象实现

4.IServiceProvider负责所有代码注入服务的获取，这里被自定义实现后就达到了替换默认容器的原理

.Net7 源码浅析之替换默认容器的原理

.Net7 源码浅析之替换默认容器的原理

概况

下一章再来拓展实现自定义容器

参考代码库来源