使用IoC动态选择接口实现 [英] Dynamic selection of interface implementation using IoC

问题描述

我有一种在运行时确定接口实现的情况。例如，我检查一个字符串，然后确定要使用哪个子类，没有IoC它看起来像下面这样：

I have a situation where the implementation of an interface is determined at runtime. For example, I check a string and then determine which subclass to use, without IoC it looks like the following:

if (fruitStr == "Apple")
{
    new AppleImpl().SomeMethod();
}
else
{
    new BananaImpl().SomeMethod();
}

两个类 AppleImpl 和 BananaImpl 是实现相同的界面，例如 IFruit 。

Both classes AppleImpl and BananaImpl are implementation of the same interface, say IFruit.

如何使用IoC /依赖注入来完成，特别是在 Castle Windsor 中？

How can this be done using IoC/dependency injection, especially in Castle Windsor?

推荐答案

这是关于依赖注入的唯一最关心的问题，并在StackOverflow上一再被问到。

This is the single most-asked question about Dependency Injection, and gets asked over and over again on StackOverflow.

简而言之，最好使用模式来解决运行时而不是试图将容器用于构成对象图的 >，这是它的所有设计。

In short, it is best to use patterns to solve runtime creation rather than trying to use the container for more than composing object graphs, which is all it is designed for.

有几种模式可以用于此，但最好的选择是使用抽象工厂，策略，或组合两者。确切的解决方案取决于实例的使用方法 - 如果您需要几个短暂的实例，并且在使用后要丢弃它们，请使用工厂，或者如果您需要在一个或多个循环，而不必每次重新创建它们。该组合是高性能和低内存消耗之间的折衷。

There are several patterns that can be used for this, but among the best options are to use Abstract Factory, Strategy, or a combination of the two. The exact solution depends on how the instance will be used - use a factory if you will be needing several short-lived instances and want to discard them after use, or use a strategy if you need to use the instances over and over again in a loop without having to recreate them each time. The combination is a tradeoff between high performance and low memory consumption.

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