当需要同一类型的多个实例时，使用“DI” [英] DI with Unity when multiple instances of the same type is needed

问题描述

我需要帮助。我使用Unity作为我的容器，我想在我的构造函数中注入两个不同的类型的实例。

I need help with this. I'm using Unity as my container and I want to inject two different instances of the same type into my constructor.

class Example
{
   Example(IQueue receiveQueue, IQueue sendQueue) {}
}

....和IQueue在我的MessageQueue类中实现。

....and IQueue is implemented in my MessageQueue class....

class MessageQueue : IQueue
{
    MessageQueue(string path) {}
}

将两个不同的MessageQueue实例注入到我的Example类中？每个要用不同路径创建的MessageQueue实例。

How can I inject two different instances of MessageQueue into my Example class? Each of the MessageQueue instances to be created with different path.

推荐答案

有很多方法来实现所需的结果（证明通过多个答案）。这是使用命名注册（没有属性）的另一种方法：

There are many ways to achieve the results you want (as evidenced by the multiple answers). Here is another way using named registrations (without attributes):

IUnityContainer container = new UnityContainer();

container.RegisterType<IQueue, MessageQueue>("ReceiveQueue", 
    new InjectionConstructor("receivePath"));

container.RegisterType<IQueue, MessageQueue>("SendQueue",
    new InjectionConstructor("sendPath"));

container.RegisterType<Example>(
    new InjectionConstructor(
        new ResolvedParameter<IQueue>("ReceiveQueue"),
        new ResolvedParameter<IQueue>("SendQueue")));

Example example = container.Resolve<Example>();

这种方法的缺点是，如果Example构造函数被更改，则还必须修改注册码匹配。此外，错误将是一个运行时错误，而不是一个更好的编译时错误。

The downside of this approach is that if the Example constructor is changed then the registration code must also be modified to match. Also, the error would be a runtime error and not a more preferable compile time error.

您可以将以上内容与InjectionFactory结合起来，以手动方式调用构造函数以给出编译时间检查：

You could combine the above with an InjectionFactory to invoke the constructor manually to give compile time checking:

IUnityContainer container = new UnityContainer();

container.RegisterType<IQueue, MessageQueue>("ReceiveQueue",
    new InjectionConstructor("receivePath"));

container.RegisterType<IQueue, MessageQueue>("SendQueue",
    new InjectionConstructor("sendPath"));

container.RegisterType<Example>(new InjectionFactory(c =>
    new Example(c.Resolve<IQueue>("ReceiveQueue"),
                c.Resolve<IQueue>("SendQueue"))));

Example example = container.Resolve<Example>();

如果您使用的是组合根，那么使用魔术字符串（ReceiveQueue和SendQueue ）将限于一个注册位置。

If you are using a composition root then the use of the magic strings ("ReceiveQueue" and "SendQueue") would be limited to the one registration location.

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