可以依赖注入prevent循环依赖？ [英] Can dependency injection prevent a circular dependency?

问题描述

项目＃1有一些项目＃2引用接口和类。

现在我想用工程＃2＃项目1的实施，但vs.net抱怨循环依赖。

如果我是使用在项目＃1依赖关系注入和绑定到项目＃2的实现（因为它符合接口的合同），将这项工作或我仍然会得到循环依赖错误消息，在运行时<？ / p>

解决方案

您也许可以的通过DI解决这个问题，但你的不应该的

如果我理解正确的话，你有这样的事情：

  大会+ A +组件B
  | |
  +  - 接口IFoo的+  - 类ConcreteFoo：IFoo的
  | ^
  +  -  MyClass类 - > -------> ------- |

在换句话说，你正在试图获得 MyClass的引用 ConcreteFoo ，但你不能因为装配 B ，其中 ConcreteFoo 驻留在已经依赖于的IFoo 在 A 。

这是一个设计错误。如果声明在大会接口的IFoo A ，但没有具体的实现，那么任何其他接口/装配类 A 应的仅参考的IFoo ，绝不会的具体类实现它。

有三种方法可以消除循环依赖：

1. 请 MyClass的依赖的IFoo 而不是 ConcreteFoo 。这可能是最好的选择，如果你能做到这一点。如果问题是，你需要的IFoo 使用的物理实例 MyClass的，不知道从哪里得到一个来自，然后把它取一个的IFoo 在构造 - 让谁使用 MyClass的找出的IFoo 使用。




2. 移动接口，以自己组装。这仍然是一个相当不错的做法。你的设计是这样的：

  

 +应用大会大会+接口+混凝土装配
      | | |
      | +  - 接口的IFoo |
      | | \\ |
      +  -  MyClass类| \\ ------ +  - 类ConcreteFoo
      | | | ^
      + ----会员美孚 - > ---------------------> ------------------- |
  

1. 将 MyClass的来自己的装配。有效地将依赖关系树看起来一样在上述第2，但如果装配 A 比 B小得多然后这将需要更少的努力。

希望有所帮助。

Project#1 has some interfaces and classes that project#2 references.

Now I want to use the implementation of Project#2 in Project#1 but vs.net complains about a circular dependency.

If I was to use dependancy injection in Project#1 and bind to the implementation in Project#2 (since it adheres to the interface contract), will this work or I will still get the circular dependency error message at runtime?

解决方案

You probably could solve this with DI, but you shouldn't.

If I understand correctly, you have something like this:

  + Assembly A           + Assembly B
  |                      |
  +-- Interface IFoo     +-- Class ConcreteFoo : IFoo
  |                                   ^
  +-- Class MyClass -->------->-------|

In other words, you're trying to get MyClass to reference ConcreteFoo, but you can't because assembly B, which ConcreteFoo resides in, already depends on IFoo in A.

This is a design error. If you declare the interface IFoo in Assembly A, but no concrete implementations, then any other interfaces/classes in assembly A should only reference IFoo, never a concrete class that implements it.

There are three ways to eliminate the circular dependency:

1. Make MyClass dependent on IFoo instead of ConcreteFoo. This is probably the best option if you can do it. If the issue is that you need a physical instance of IFoo for use in MyClass and don't know where to get one from, then have it take an IFoo in the constructor - let whoever uses MyClass figure out what IFoo to use.

2. Move the interfaces to their own assembly. This is still a reasonably good practice. Your design will look like this:

  + Assembly App       + Assembly Interfaces      + Assembly Concrete
      |                    |                          |
      |                    +-- Interface IFoo         |
      |                    |                  \       |
      +-- Class MyClass    |                   \------+-- Class ConcreteFoo
      |                    |                          |           ^
      +---- Member Foo ->--------------------->-------------------|
  

1. Move MyClass to its own assembly. Effectively your dependency tree will look the same as in #2 above, but if assembly A is much smaller than B then this would require less effort.

Hope that helps.

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