c# – 介体模式和简单注入器的逆变

这个问题起源于我正在尝试为MediatR：https://github.com/jbogard/MediatR/pull/14创建一个简单的注入器实现.

我在尝试解决通用处理程序接口的实现时遇到了麻烦.考虑以下通知处理程序接口：

public interface INotificationHandler<in TNotification>
    where TNotification : INotification
{
    void Handle(TNotification notification);
}

INotifcation只是一个空的标记界面.

我为Pinged(实现INotification)事件定义了以下处理程序：

public class PingedHandler : INotificationHandler<Pinged>
{
    public void Handle(Pinged notification) { }
}

public class PingedHandler2 : INotificationHandler<Pinged>
{
    public void Handle(Pinged notification) { }
}

还有一个通用的处理程序(注意这应该处理每个INotification)：

public class GenericHandler : INotificationHandler<INotification>
{
    public void Handle(INotification notification) { }
}

通过以下注册：

var container = new Container();

container.RegisterManyForOpenGeneric(
    typeof (INotificationHandler<>),
    (service, impls) => container.RegisterAll(service, impls),
    AppDomain.CurrentDomain.GetAssemblies());

现在我期待：

GetAllInstances<INotificationHandler<Pinged>>();

解决它所做的PingedHandler和PingedHandler2.但它没有解析GenericHandler,因为它实现了INotificationHandler< INotification>而不是INotificationHandler< Pinged>.我想知道是否有办法让Simple Injector搜索整个对象图并解决任何Pinged.

我从史蒂文发现了a blog post关于协方差和反方差的问题,但是我无法让它适用于我的例子.

解决方法:

UPDATE

从Simple Injector版本开始,2.7 this functionality现已成为标准配置,您不再需要下面显示的解决方法.

您缺少该文章中描述的MultipleDispatchEventHandler的变体.采用基本逻辑并将其应用于抽象确实可以得到您期望的结果：

[Fact]
public void RegisterAll_Contravariant_Succeeds()
{
    var container = new Container();

    container.RegisterManyForOpenGeneric(
        typeof(INotificationHandler<>),
        (service, impls) => container.RegisterAll(service, impls),
        AppDomain.CurrentDomain.GetAssemblies());

    var handlersType = typeof(IEnumerable<INotificationHandler<Pinged>>);

    var handlersCollection = (
        from r in container.GetCurrentRegistrations()
        where handlersType.IsAssignableFrom(r.ServiceType)
        select r.GetInstance())
        .Cast<IEnumerable<INotificationHandler<Pinged>>>()
        .ToArray();

    var result = 
        from handlers in handlersCollection
        from handler in handlers
        select handler;

    Assert.Equal(3, result.Count());
}

但是使GenericHandler变得通用可能更容易：

public class GenericHandler<TNotification> : INotificationHandler<TNotification>
    where TNotification : INotification
{
    public void Handle(TNotification notification) { }
}

提供更简单的注册

[Fact]
public void RegisterAll_WithOpenAndClosedGenerics_Succeeds()
{
    var container = new Container();

    var types = OpenGenericBatchRegistrationExtensions
        .GetTypesToRegister(
            container,
            typeof(INotificationHandler<>),
            AccessibilityOption.AllTypes,
            AppDomain.CurrentDomain.GetAssemblies())
        .ToList();

    types.Add(typeof(GenericHandler<>));

    container.RegisterAll(typeof(INotificationHandler<>), types);

    var result = container.GetAllInstances<INotificationHandler<Pinged>>().ToList();

    Assert.Equal(3, result.Count());
}

标签：c,simple-injector,mediator,mediatr
来源： https://codeday.me/bug/20190609/1206252.html