前言
包含服務註冊信息IServiceCollection 集合最終被用來創建作爲依賴注入容器的IServiceProvider 對象。
當需要創建某個服務實例的時候(服務消費)，我們通過指定服務類型調用IServiceProvider 接口GetService 方法即可。
那麼來看下和IServiceProvider 相關的東西吧。
IServiceProvider
這裏面只有一個提供服務的方法:
/// <summary>Defines a mechanism for retrieving a service object; that is, an object that provides custom support to other objects.</summary>
public interface IServiceProvider
{
/// <summary>Gets the service object of the specified type.</summary>
/// <param name="serviceType">An object that specifies the type of service object to get.</param>
/// <returns>A service object of type <paramref name="serviceType">serviceType</paramref>.
/// -or-
/// null if there is no service object of type <paramref name="serviceType">serviceType</paramref>.</returns>
object GetService(Type serviceType);
}
在創建IServiceProvider的對象創建上，有三個構造函數:
public static class ServiceCollectionContainerBuilderExtensions
{
/// <summary>
/// Creates a <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" /> containing services from the provided <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />.
/// </summary>
/// <param name="services">The <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" /> containing service descriptors.</param>
/// <returns>The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" />.</returns>
public static ServiceProvider BuildServiceProvider(this IServiceCollection services)
{
return services.BuildServiceProvider(ServiceProviderOptions.Default);
}
/// <summary>
/// Creates a <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" /> containing services from the provided <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />
/// optionally enabling scope validation.
/// </summary>
/// <param name="services">The <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" /> containing service descriptors.</param>
/// <param name="validateScopes">
/// <c>true</c> to perform check verifying that scoped services never gets resolved from root provider; otherwise <c>false</c>.
/// </param>
/// <returns>The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" />.</returns>
public static ServiceProvider BuildServiceProvider(this IServiceCollection services, bool validateScopes)
{
return services.BuildServiceProvider(new ServiceProviderOptions
{
ValidateScopes = validateScopes
});
}
/// <summary>
/// Creates a <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" /> containing services from the provided <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />
/// optionally enabling scope validation.
/// </summary>
/// <param name="services">The <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" /> containing service descriptors.</param>
/// <param name="options">
/// Configures various service provider behaviors.
/// </param>
/// <returns>The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" />.</returns>
public static ServiceProvider BuildServiceProvider(this IServiceCollection services, ServiceProviderOptions options)
{
//IL_0008: Unknown result type (might be due to invalid IL or missing references)
//IL_0016: Unknown result type (might be due to invalid IL or missing references)
if (services == null)
{
throw new ArgumentNullException("services");
}
if (options == null)
{
throw new ArgumentNullException("options");
}
return new ServiceProvider((IEnumerable<ServiceDescriptor>)services, options);
}
}
我們看到無論其如何構造，那麼都有一個ServiceProviderOptions配置類。
這個配置我前面8中解釋過，就是對注入服務的範圍檢測。
那麼還有一個重要的問題，難道我們只能根據getservice 去獲取服務對象？來看看獲取服務的擴展。
查看ServiceProviderServiceExtensions類:
裏面有一些:
public static T GetService<T>(this IServiceProvider provider)
{
//IL_0008: Unknown result type (might be due to invalid IL or missing references)
if (provider == null)
{
throw new ArgumentNullException("provider");
}
return (T)provider.GetService(Type.GetTypeFromHandle(typeof(T).TypeHandle));
}
/// <summary>
/// Get service of type <paramref name="serviceType" /> from the <see cref="T:System.IServiceProvider" />.
/// </summary>
/// <param name="provider">The <see cref="T:System.IServiceProvider" /> to retrieve the service object from.</param>
/// <param name="serviceType">An object that specifies the type of service object to get.</param>
/// <returns>A service object of type <paramref name="serviceType" />.</returns>
/// <exception cref="T:System.InvalidOperationException">There is no service of type <paramref name="serviceType" />.</exception>
public static object GetRequiredService(this IServiceProvider provider, Type serviceType)
{
//IL_0008: Unknown result type (might be due to invalid IL or missing references)
//IL_001c: Unknown result type (might be due to invalid IL or missing references)
//IL_0044: Unknown result type (might be due to invalid IL or missing references)
if (provider == null)
{
throw new ArgumentNullException("provider");
}
if (serviceType == (Type)null)
{
throw new ArgumentNullException("serviceType");
}
ISupportRequiredService supportRequiredService = provider as ISupportRequiredService;
if (supportRequiredService != null)
{
return supportRequiredService.GetRequiredService(serviceType);
}
object service = provider.GetService(serviceType);
if (service == null)
{
throw new InvalidOperationException(Resources.FormatNoServiceRegistered(serviceType));
}
return service;
}
/// <summary>
/// Get service of type <typeparamref name="T" /> from the <see cref="T:System.IServiceProvider" />.
/// </summary>
/// <typeparam name="T">The type of service object to get.</typeparam>
/// <param name="provider">The <see cref="T:System.IServiceProvider" /> to retrieve the service object from.</param>
/// <returns>A service object of type <typeparamref name="T" />.</returns>
/// <exception cref="T:System.InvalidOperationException">There is no service of type <typeparamref name="T" />.</exception>
public static T GetRequiredService<T>(this IServiceProvider provider)
{
//IL_0008: Unknown result type (might be due to invalid IL or missing references)
if (provider == null)
{
throw new ArgumentNullException("provider");
}
return (T)provider.GetRequiredService(Type.GetTypeFromHandle(typeof(T).TypeHandle));
}
/// <summary>
/// Get an enumeration of services of type <typeparamref name="T" /> from the <see cref="T:System.IServiceProvider" />.
/// </summary>
/// <typeparam name="T">The type of service object to get.</typeparam>
/// <param name="provider">The <see cref="T:System.IServiceProvider" /> to retrieve the services from.</param>
/// <returns>An enumeration of services of type <typeparamref name="T" />.</returns>
public static IEnumerable<T> GetServices<T>(this IServiceProvider provider)
{
//IL_0008: Unknown result type (might be due to invalid IL or missing references)
if (provider == null)
{
throw new ArgumentNullException("provider");
}
return provider.GetRequiredService<IEnumerable<T>>();
}
其餘的可以自己去查看。
服務的創建
我們知道服務的創建一般都是ioc自動選擇的，那麼假如我們一個class 裏面有多個構造函數，那麼會選擇哪一個呢?
public interface IFoo { }
public interface IBar { }
public interface IBaz { }
public interface IQux { }
public class Foo : IFoo { }
public class Bar : IBar { }
public class Baz : IBaz { }
public class Qux : IQux
{
public Qux(IFoo foo) => Console.WriteLine("Selected constructor: Qux(IFoo)");
public Qux(IFoo foo, IBar bar) => Console.WriteLine("Selected constructor: Qux(IFoo, IBar)");
public Qux(IFoo foo, IBar bar, IBaz baz) => Console.WriteLine("Selected constructor: Qux(IFoo, IBar, IBaz)");
}
static void Main()
{
new ServiceCollection()
.AddTransient<IFoo, Foo>()
.AddTransient<IBar, Bar>()
.AddTransient<IQux, Qux>()
.BuildServiceProvider()
.GetServices<IQux>();
Console.ReadKey();
}
上面Qux有三個控制類，那麼選擇哪一個呢?
看下結果:
那麼爲什麼會是這一個呢?
第一:IBaz類型沒有註冊，那麼會排除掉Qux(IFoo foo, IBar bar, IBaz baz)
第二就是裏面的一個規則:每一個候選構造參數類型的集合都是這個構造函數參數類型的子集。
好的，那麼好了，剩下:Qux(IFoo foo, IBar bar) 包含了Qux(IFoo foo) 那麼就是Qux(IFoo foo, IBar bar)，如果沒有包含全部子集的那麼就會報錯。
Qux(IFoo foo, IBar bar) 也就是超集的意思。
改一下:
public interface IFoo { }
public interface IBar { }
public interface IBaz { }
public interface IQux { }
public class Foo : IFoo { }
public class Bar : IBar { }
public class Baz : IBaz { }
public class Qux : IQux
{
public Qux(IFoo foo, IBaz baz) => Console.WriteLine("Selected constructor: Qux(IFoo, IBar)");
public Qux(IFoo foo, IBar bar) => Console.WriteLine("Selected constructor: Qux(IFoo, IBar, IBaz)");
}
static void Main()
{
new ServiceCollection()
.AddTransient<IFoo, Foo>()
.AddTransient<IBar, Bar>()
.AddTransient<IBaz,Baz>()
.AddTransient<IQux, Qux>()
.BuildServiceProvider()
.GetServices<IQux>();
Console.ReadKey();
}
這時候報錯爲:
下一節
服務的生命週期