标签：dependency-injection c expression-trees simple-injector
如何注入IEnumerable< Func< T>使用简单注射器？
仅添加一些上下文,我试图创建所有知道如何处理一个特定事件的EventHandlers.这是我的容器注册：
container.RegisterCollection(typeof(IHandleDomainEvent<>),
AppDomain.CurrentDomain.GetAssemblies());
这里是实现IHandleEvent< T>的两个类.相同事件的界面：
public class Reservation : IHandleDomainEvent<OrderConfirmed>{}
public class Order: IHandleDomainEvent<OrderConfirmed>{}
因此,当我调用简单注入器时：
var handlers = _container.GetAllInstances<Func<IHandleDomainEvent<OrderConfirmed>>>();
我想接收IEnumerable< Func< IHandleDomainEvent< OrderConfirmed>>
为了澄清,我知道如果我打电话：
var handlers = _container.GetAllInstances<IHandleDomainEvent<OrderConfirmed>>();
我会得到IEnumerable< IHandleDomainEvent< OrderConfirmed>>.
对于只有一种实现的接口,请使用以下命令进行注册：
container.Register(typeof(IHandleDomainEvent<>),
AppDomain.CurrentDomain.GetAssemblies(), Lifestyle.Scoped);
并将以下ResolveUnregisteredType添加到注册的末尾：
container.ResolveUnregisteredType += (o, args) => ResolveFuncOfT(o, args, container);
// Function
private static void ResolveFuncOfT(object s, UnregisteredTypeEventArgs e, Container container)
{
var type = e.UnregisteredServiceType;
if (!type.IsGenericType || type.GetGenericTypeDefinition() != typeof(Func<>)) return;
Type serviceType = type.GetGenericArguments().First();
InstanceProducer producer = container.GetRegistration(serviceType, true);
Type funcType = typeof(Func<>).MakeGenericType(serviceType);
var factoryDelegate = Expression.Lambda(funcType, producer.BuildExpression()).Compile();
e.Register(Expression.Constant(factoryDelegate));
}
将允许调用：
var handler = _container.GetInstance<Func<IHandleDomainEvent<TEvent>>>();
解决方法:
这就是Simple Injector的优点：您永远不必解析IEnumerable< Func< T>>.因为任何IEnumerable< T>由Simple Injector解决的问题已充当流.
这意味着,当您解析IEnumerable< T>时,将不会解析该流的任何元素.它们仅在迭代可枚举时得到解决,并且被一对一解决.
迭代流时,将根据元素的生活方式对其进行解析.这意味着当集合中的元素为瞬态时,对流进行两次迭代将导致创建新的瞬态实例.
例：
// Only resolves the enumerable, not the contained handlers.
// This enumerable itself is a singleton, you can reference it forever.
var collection = container.GetInstances<IEventHandler<OrderConfirmed>>();
// Calls back into the container to get the first element, but nothing more
var first = collection.First();
// Since the stream that Simple Injector returns is a IList<T>, getting the last
// element is an O(1) operation, meaning that only the last element is resolved;
// not the complete collection.
var last = collection.Last();
// Calling .ToArray(), however, will obviously resolve all registrations that are
// part of the collection.
var all = collection.ToArray();
// Iterating a stream will always call back into the container, which ensures
// that the stream adheres to the elements lifestyles. Transients will be
// created on each iteration, while singletons will only be created once.
container.Register<Apple>(Lifestyle.Transient);
container.Register<Banana>(Lifestyle.Singleton);
container.RegisterCollection<IFruit>(typeof(Apple), typeof(Banana));
var fruits = container.GetAllInstances<IFruit>();
Assert.AreNotSame(fruits.First(), fruits.First());
Assert.AreSame(fruits.Last(), fruits.Last());
// Even other collection types such as IReadOnlyCollection<T> behave as streams
var col = container.GetInstance<IReadOnlyCollection<IEventHandler<OrderConfirmed>>();
// This gives you the possibility to get a particular item by its index.
var indexedItem = col[3];
您可以在此处找到有关在Simple Injector中使用集合的更多信息：
> Simple Injector Documentation – Using – Collection types
> Simple Injector Documentation – Advanced – Auto-Registration
> Simple Injector Documentation – Design Decisions –
The API clearly differentiates the registration of collections
标签：dependency-injection,c,expression-trees,simple-injector 来源： https://codeday.me/bug/20191025/1927137.html
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