前言
在该系列六中介绍了一个简单的依赖注入，该节介绍.net core 中的依赖注入的服务注入。
ServiceDescriptor
ServiceDescriptor 是服务描述的意思，这个是做什么的呢？
我们知道当我们要实例化一个服务的时候，我们通过serviceType 属性去查找，是否我们注册了。
那么通过serviceType 查找到的是什么呢?就是这个ServiceDescriptor,好了那么分析一下这个serviceDescriptor 到底是什么吧。
来看一下又什么属性吧!
public ServiceLifetime Lifetime
{
[CompilerGenerated]
get;
}
/// <inheritdoc />
public Type ServiceType
{
[CompilerGenerated]
get;
}
/// <inheritdoc />
public Type ImplementationType
{
[CompilerGenerated]
get;
}
/// <inheritdoc />
public object ImplementationInstance
{
[CompilerGenerated]
get;
}
/// <inheritdoc />
public Func<IServiceProvider, object> ImplementationFactory
{
[CompilerGenerated]
get;
}
下面来介绍一下属性。
Lifetime 这个我想不用介绍了吧，生命周期。
public enum ServiceLifetime
{
/// <summary>
/// Specifies that a single instance of the service will be created.
/// </summary>
Singleton,
/// <summary>
/// Specifies that a new instance of the service will be created for each scope.
/// </summary>
/// <remarks>
/// In ASP.NET Core applications a scope is created around each server request.
/// </remarks>
Scoped,
/// <summary>
/// Specifies that a new instance of the service will be created every time it is requested.
/// </summary>
Transient
}
ServiceType,我想我也不用介绍的，就是当前注入类型，比如说IFoo
然后呢，下面三种属性体现了，提供服务实例的三种方式:
/// <inheritdoc />
public Type ImplementationType
{
[CompilerGenerated]
get;
}
/// <inheritdoc />
public object ImplementationInstance
{
[CompilerGenerated]
get;
}
/// <inheritdoc />
public Func<IServiceProvider, object> ImplementationFactory
{
[CompilerGenerated]
get;
}
这个需要我们来看下这个的时候ServiceDescriptor的构造函数。
/// <summary>
/// Initializes a new instance of <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceDescriptor" /> with the specified <paramref name="implementationType" />.
/// </summary>
/// <param name="serviceType">The <see cref="T:System.Type" /> of the service.</param>
/// <param name="implementationType">The <see cref="T:System.Type" /> implementing the service.</param>
/// <param name="lifetime">The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceLifetime" /> of the service.</param>
public ServiceDescriptor(Type serviceType, Type implementationType, ServiceLifetime lifetime)
: this(serviceType, lifetime)
{
//IL_0016: Unknown result type (might be due to invalid IL or missing references)
//IL_002a: Unknown result type (might be due to invalid IL or missing references)
if (serviceType == (Type)null)
{
throw new ArgumentNullException("serviceType");
}
if (implementationType == (Type)null)
{
throw new ArgumentNullException("implementationType");
}
ImplementationType = implementationType;
}
/// <summary>
/// Initializes a new instance of <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceDescriptor" /> with the specified <paramref name="instance" />
/// as a <see cref="F:Microsoft.Extensions.DependencyInjection.ServiceLifetime.Singleton" />.
/// </summary>
/// <param name="serviceType">The <see cref="T:System.Type" /> of the service.</param>
/// <param name="instance">The instance implementing the service.</param>
public ServiceDescriptor(Type serviceType, object instance)
: this(serviceType, ServiceLifetime.Singleton)
{
//IL_0016: Unknown result type (might be due to invalid IL or missing references)
//IL_0024: Unknown result type (might be due to invalid IL or missing references)
if (serviceType == (Type)null)
{
throw new ArgumentNullException("serviceType");
}
if (instance == null)
{
throw new ArgumentNullException("instance");
}
ImplementationInstance = instance;
}
/// <summary>
/// Initializes a new instance of <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceDescriptor" /> with the specified <paramref name="factory" />.
/// </summary>
/// <param name="serviceType">The <see cref="T:System.Type" /> of the service.</param>
/// <param name="factory">A factory used for creating service instances.</param>
/// <param name="lifetime">The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceLifetime" /> of the service.</param>
public ServiceDescriptor(Type serviceType, Func<IServiceProvider, object> factory, ServiceLifetime lifetime)
: this(serviceType, lifetime)
{
//IL_0016: Unknown result type (might be due to invalid IL or missing references)
//IL_0024: Unknown result type (might be due to invalid IL or missing references)
if (serviceType == (Type)null)
{
throw new ArgumentNullException("serviceType");
}
if (factory == null)
{
throw new ArgumentNullException("factory");
}
ImplementationFactory = factory;
}
我们看到了这三个构造方法，那么我们基本明白了，到时候创建服务实例的时候就是这几种方法了。
这里面有一个值得注意的地方，就是:
public ServiceDescriptor(Type serviceType, object instance)
: this(serviceType, ServiceLifetime.Singleton)
{
//IL_0016: Unknown result type (might be due to invalid IL or missing references)
//IL_0024: Unknown result type (might be due to invalid IL or missing references)
if (serviceType == (Type)null)
{
throw new ArgumentNullException("serviceType");
}
if (instance == null)
{
throw new ArgumentNullException("instance");
}
ImplementationInstance = instance;
}
也就是说我们可以直接让接口对应实例，比如说:new ServiceDescriptor(IFoo,new Foo());默认的生命周期模式就是:ServiceLifetime.Singleton
IServiceCollection
依赖存储框架将服务注册存储在一个通过IServiceCollection 接口表示的集合中。
public interface IServiceCollection : IList<ServiceDescriptor>, ICollection<ServiceDescriptor>, IEnumerable<ServiceDescriptor>, IEnumerable```
{
}
在 IServiceCollection 中，本质上其实就是一个ServiceDescriptor集合。
那么来看下IServiceCollection的实例对象ServiceCollection的扩展方法ServiceCollectionServiceExtensions。
private static IServiceCollection Add(IServiceCollection collection, Type serviceType, Type implementationType, ServiceLifetime lifetime)
{
ServiceDescriptor serviceDescriptor = new ServiceDescriptor(serviceType, implementationType, lifetime);
((ICollection<ServiceDescriptor>)collection).Add(serviceDescriptor);
return collection;
}
private static IServiceCollection Add(IServiceCollection collection, Type serviceType, Func<IServiceProvider, object> implementationFactory, ServiceLifetime lifetime)
{
ServiceDescriptor serviceDescriptor = new ServiceDescriptor(serviceType, implementationFactory, lifetime);
((ICollection<ServiceDescriptor>)collection).Add(serviceDescriptor);
return collection;
}
可以帮助我们直接创建ServiceDescriptor,并且加入到当前的ServiceCollection 中。
然后ServiceCollectionServiceExtensions 在3.0在还更新了，tryadd，因为我们一个ServiceType 可以对应多个，使用tryadd 的时候，就会尝试加入，如果有的话就不会加入。
在ServiceCollection和ServiceCollectionServiceExtensions 有一些其他的方法，最好去看一下源码，了解一下。
总结
下一章依赖注入的服务消费