Csharp 使用DI实例化带有动态参数的服务

我如何注册MyClass与DI，但有一个选项，以传递someRandomInput每次我需要得到一个实例？

假设只需要指定一次someRandomInput，那么您可以在服务注册的implementationFactory:中这样做:

IConfiguration cfg = ...

//

services
    .AddSingleton<MyClass>( implementationFactory: ( IServiceProvider sp ) =>
        new MyClass(
            srs            : sp.GetRequiredService<SomeRequiredService>(),
            someRandomInput: cfg.GetString("Foobars")
        )
    );

同样适用于AddTransient和AddScoped-问题是它们都将使用您在工厂中传递到someRandomInput的任何值-尽管您的工厂方法本身也可以使用IServiceProvider来获取another服务作为这些值的来源.

更普遍的是，这里有两种方法:

选项1:定义表示服务的数据依赖关系的接口

public interface IFoobarsServiceRequisite
{
    String GetNextStringValue();
}

public class FoobarsService
{
    public FoobarsService( SomeRequiredService srs, IFoobarsServiceRequisite requisiteData )
    {
    }
}

...然后您将注册那个Requisite服务接口的一些实现.

Option 2: Not-quite-as-bad-as AbstractSingletonProxyFactoryBean

(In case anyone missed the reference)

services
    .AddSingleton<SomeRequiredService>()
    .AddSingleton<ISomeRandomStringSource,DefaultSomeRandomStringSource>()
    .AddSingleton<IFoobarsServiceFactory,DefaultFoobarsServiceFactory>()
    .AddTransient<FoobarsService>( sp => sp.GetRequiredService<IFoobarsServiceFactory>().CreateFoobar() );


//

public interface IFoobarsServiceFactory
{
    FoobarsService CreateFoobar();
}

public class DefaultFoobarsServiceFactory : IFoobarsServiceFactory
{
    private readonly SomeRequiredService     srs;
    private readonly ISomeRandomStringSource src;

    public DefaultFoobarsServiceFactory(
        SomeRequiredService srs,
        ISomeRandomStringSource src
    )
    {
        this.srs = srs;
        this.src = src;
    }

    public FoobarsService CreateFoobar()
    {
        return new FoobarsService( this.srs, this.src.GetNextValue() );
    }
}

public class FoobarsService
{
    public FoobarsService( SomeRequiredService srs, String someRandomValue )
    {
    }
}

所有的工厂都是这样.

我感到惊讶的是，MEDI仍然缺乏一个标准化的IServiceFactory接口来处理尴尬的边缘情况，这些情况需要比简单的sp => lambda更多的工厂逻辑，但在应用程序代码中没有need显式调用它们的.CreateService()方法-特别是EF已经有了自己的IDbContextFactory类型.

更新:选项3:工厂服务与呼叫者提供的参数

在澄清了 comments 中的事情后，我认为Op的目标是这样的:

• FoobarServiceFactory(或其interface)是一个普通的Singleton服务，它有FoobarService个依赖项，但也允许/要求FoobarServiceFactory的使用者提供他们自己的参数，说明他们何时想要获得FoobarService的实例，如下所示:

services.AddSingleton<IFoobarServiceFactory,FoobarServiceFactory>()

//

public interface IFoobarServiceFactory // Note that this interface is entirely optional: you could just register `FoobarServiceFactory` as a service.
{
    FoobarsService CreateFoobar( String callerProvidedData );
}

public class FoobarServiceFactory: IFoobarServiceFactory
{
    private readonly SomeRequiredService srs;

    public DefaultFoobarsServiceFactory( SomeRequiredService srs )
    {
        this.srs = srs;
    }

    public FoobarsService CreateFoobar( String callerProvidedData )
    {
        return new FoobarService( this.srs, callerProvidedData );
    }
}

public class FoobarService
{
    public FoobarService( SomeRequiredService srs, String someRandomValue )
    {
        // etc
    }
}

用法如下:

public class SomeConsumer
{
    private readonly IFoobarServiceFactory fbFactory;

    public SomeConsumer( IFoobarServiceFactory fbFactory )
    {
        this.fbFactory = fbFactory;
    }

    public void DoSomething()
    {
        String someRandomString = Math.Random() > 0.5 ? "abc" : "0xdeadbeef";
        
        FoobarService svc = this.fbFactory.Create( someRandomString );
        // do stuff with `svc`
    }
}

IFoobarServiceFactory的替代实现可以使用IServiceProvider，如果不可能为SomeRequiredService保留长生命周期 (或未绑定的生命周期 )(并且IMO，这是需要IServiceProvider作为实际依赖的唯一可接受的原因(除了依赖关系图中的中断循环，ofc):

public class AltFoobarServiceFactory : IFoobarServiceFactory
{
    private readonly IServiceProvider sp;

    public AltFoobarServiceFactory( IServiceProvider sp )
    {
        this.sp = sp;
    }

    public FoobarsService CreateFoobar( String callerProvidedData )
    {
        // `ActivatorUtilities` is useful! https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.dependencyinjection.activatorutilities?view=dotnet-plat-ext-8.0
        return ActivatorUtilities.CreateInstance<FoobarsService>( sp, callerProvidedData );
    }
}