.netcore之核心组件

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Microsoft.Extensions.DependencyInjection.Abstractions;
Microsoft.Extensions.DependencyInjection;

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public class ServiceDescriptor
{
    public Type ImplementationType { get; }
    public object ImplementationInstance { get; }
    public Func<IServiceProvider, object> ImplementationFactory { get; }
    public ServiceLifetime Lifetime { get; }
    public Type ServiceType { get; }
}

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public interface IServiceCollection : ICollection<ServiceDescriptor>, IEnumerable<ServiceDescriptor>, IEnumerable, IList<ServiceDescriptor>
{
}

public class ServiceCollection : IServiceCollection, ICollection<ServiceDescriptor>, IEnumerable<ServiceDescriptor>, IEnumerable, IList<ServiceDescriptor>
{
    public ServiceCollection();

    public ServiceDescriptor this[int index] { get; set; }

    public int Count { get; }
    public bool IsReadOnly { get; }

    public void Clear();
    public bool Contains(ServiceDescriptor item);
    public void CopyTo(ServiceDescriptor[] array, int arrayIndex);
    public IEnumerator<ServiceDescriptor> GetEnumerator();
    public int IndexOf(ServiceDescriptor item);
    public void Insert(int index, ServiceDescriptor item);
    public bool Remove(ServiceDescriptor item);
    public void RemoveAt(int index);
}

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var serviceDescriptor = ServiceDescriptor.Singleton<IMyService, MyService>();
services.Add(serviceDescriptor);

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IServiceCollection services = new ServiceCollection();

// 指定实例
services.AddSingleton<IMyService>(new MyService());

// 指定类型
services.AddSingleton<IMyService, MyService>();

// 工厂模式
services.AddScoped<IMyService>(provider => new MyService());

// 工厂模式， 从容器中获取
services.AddTransient<IMyService>(provider => new MyService());
services.AddTransient<IMyService>(provider => provider.GetService<MyService>());

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public interface IServiceProvider
{
    //
    // Summary:
    //     Gets the service object of the specified type.
    //
    // Parameters:
    //   serviceType:
    //     An object that specifies the type of service object to get.
    //
    // Returns:
    //     A service object of type serviceType. -or- null if there is no service object
    //     of type serviceType.
    object GetService(Type serviceType);
}

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假设已经注册好的服务也获得了IServiceProvider实例: 
IServiceCollection services = new ServiceCollection();
// 忽略服务注册的代码

IServiceProvider serviceProvider = services.BuildServiceProvider();

获取服务实例的代码如下：

// 指定类型获取服务实例
object myService = serviceProvider.GetService(typeof(IMyService));

// 泛型方法指定类型获取服务实例
IMyService myService = serviceProvider.GetService<IMyService>();

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// 指定类型获取服务实例
object myService = serviceProvider.GetRequiredService(typeof(IMyService));

// 泛型方法指定类型获取服务实例
IMyService myService = serviceProvider.GetRequiredService<IMyService>();

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// 指定类型, 获取object实例集合
IEnumerable<object> myServiceList = serviceProvider.GetService(typeof(IMyService));

// 泛型方法, 获取指定类型的实例集合
IEnumerable<T> myServiceList = serviceProvider.GetService<T>();

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public class Startup
{
    // some code
	 public void ConfigureServices(IServiceCollection services)
     {
		// 服务注册
     }
    
     public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
     {
          // 根容器
          var rootServiceProvider = app.ApplicationServices; 
         // some code
     }
}

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public interface IApplicationBuilder
{
    //
    // Summary:
    //     Gets or sets the System.IServiceProvider that provides access to the application's
    //     service container.
    IServiceProvider ApplicationServices { get; set; }
    //
    // Summary:
    //     Gets a key/value collection that can be used to share data between middleware.
    IDictionary<string, object> Properties { get; }
    //
    // Summary:
    //     Gets the set of HTTP features the application's server provides.
    IFeatureCollection ServerFeatures { get; }

    //
    // Summary:
    //     Builds the delegate used by this application to process HTTP requests.
    //
    // Returns:
    //     The request handling delegate.
    RequestDelegate Build();
    //
    // Summary:
    //     Creates a new Microsoft.AspNetCore.Builder.IApplicationBuilder that shares the
    //     Microsoft.AspNetCore.Builder.IApplicationBuilder.Properties of this Microsoft.AspNetCore.Builder.IApplicationBuilder.
    //
    // Returns:
    //     The new Microsoft.AspNetCore.Builder.IApplicationBuilder.
    IApplicationBuilder New();
    //
    // Summary:
    //     Adds a middleware delegate to the application's request pipeline.
    //
    // Parameters:
    //   middleware:
    //     The middleware delegate.
    //
    // Returns:
    //     The Microsoft.AspNetCore.Builder.IApplicationBuilder.
    IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware);
}

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public interface IServiceScope : IDisposable
{
    //
    // Summary:
    //     The System.IServiceProvider used to resolve dependencies from the scope.
    IServiceProvider ServiceProvider { get; }
}

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IServiceCollection services = new ServiceCollection();

// ignore service register code here
IServiceProvider serviceProvider = services.BuildServiceProvider();

// 创建了子容器
IServiceScope scope = serviceProvider.CreateScope();

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public interface IServiceScopeFactory
{
    //
    // Summary:
    //     Create an Microsoft.Extensions.DependencyInjection.IServiceScope which contains
    //     an System.IServiceProvider used to resolve dependencies from a newly created
    //     scope.
    //
    // Returns:
    //     An Microsoft.Extensions.DependencyInjection.IServiceScope controlling the lifetime
    //     of the scope. Once this is disposed, any scoped services that have been resolved
    //     from the Microsoft.Extensions.DependencyInjection.IServiceScope.ServiceProvider
    //     will also be disposed.
    IServiceScope CreateScope();
}

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public enum ServiceLifetime
{
    //
    // Summary:
    //     Specifies that a single instance of the service will be created.
    Singleton = 0,
    //
    // Summary:
    //     Specifies that a new instance of the service will be created for each scope.
    //
    // Remarks:
    //     In ASP.NET Core applications a scope is created around each server request.
    Scoped = 1,
    //
    // Summary:
    //     Specifies that a new instance of the service will be created every time it is
    //     requested.
    Transient = 2
}

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public abstract class HttpContext
{
        protected HttpContext();
        //
        // Summary:
        //     Gets information about the underlying connection for this request.
        public abstract ConnectionInfo Connection { get; }
        //
        // Summary:
        //     Gets the collection of HTTP features provided by the server and middleware available
        //     on this request.
        public abstract IFeatureCollection Features { get; }
        //
        // Summary:
        //     Gets or sets a key/value collection that can be used to share data within the
        //     scope of this request.
        public abstract IDictionary<object, object> Items { get; set; }
        //
        // Summary:
        //     Gets the Microsoft.AspNetCore.Http.HttpRequest object for this request.
        public abstract HttpRequest Request { get; }
        //
        // Summary:
        //     Notifies when the connection underlying this request is aborted and thus request
        //     operations should be cancelled.
        public abstract CancellationToken RequestAborted { get; set; }
        //
        // Summary:
        //     Gets or sets the System.IServiceProvider that provides access to the request's
        //     service container.
        public abstract IServiceProvider RequestServices { get; set; }
        //
        // Summary:
        //     Gets the Microsoft.AspNetCore.Http.HttpResponse object for this request.
        public abstract HttpResponse Response { get; }
        //
        // Summary:
        //     Gets or sets the object used to manage user session data for this request.
        public abstract ISession Session { get; set; }
        //
        // Summary:
        //     Gets or sets a unique identifier to represent this request in trace logs.
        public abstract string TraceIdentifier { get; set; }
        //
        // Summary:
        //     Gets or sets the user for this request.
        public abstract ClaimsPrincipal User { get; set; }
        //
        // Summary:
        //     Gets an object that manages the establishment of WebSocket connections for this
        //     request.
        public abstract WebSocketManager WebSockets { get; }
        //
        // Summary:
        //     Aborts the connection underlying this request.
        public abstract void Abort();
}

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public interface IServiceProviderFactory<TContainerBuilder>
{
    //
    // Summary:
    //     Creates a container builder from an Microsoft.Extensions.DependencyInjection.IServiceCollection.
    //
    // Parameters:
    //   services:
    //     The collection of services
    //
    // Returns:
    //     A container builder that can be used to create an System.IServiceProvider.
    TContainerBuilder CreateBuilder(IServiceCollection services);
    //
    // Summary:
    //     Creates an System.IServiceProvider from the container builder.
    //
    // Parameters:
    //   containerBuilder:
    //     The container builder
    //
    // Returns:
    //     An System.IServiceProvider
    IServiceProvider CreateServiceProvider(TContainerBuilder containerBuilder);
}

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 public void ConfigureServices(IServiceCollection services)
 {
     services.AddControllers().AddControllersAsServices();   
 }