依赖注入可以防止循环依赖吗？ [英] Can dependency injection prevent a circular dependency?

问题描述

现在我想在Project＃1中使用Project＃2的实现，但是网络抱怨循环依赖。

如果我在Project＃1中使用依赖注入，并绑定到Project＃2中的实现（因为它遵守了接口合同），这个工作还是我会在运行时得到循环依赖错误消息？

解决方案

你可能 / em>用DI解决这个问题，但是你不应该。

如果我理解正确，你有这样的东西：

 
 +大会A +大会B 
 | | 
 +  - 接口IFoo +  -  Class ConcreteFoo：IFoo 
 | ^ 
 +  -  Class MyClass  - > -------> ------- | 
 

换句话说，你试图获得 MyClass 来引用 ConcreteFoo ，但是不能因为程序集 B ，其中 ConcreteFoo 居住在，已经取决于 IFoo 在 A 。

这是一个设计错误。如果您在程序集 A 中声明了接口 IFoo ，但没有具体的实现，则汇编程序中的任何其他接口/ code> A 应该仅引用 IFoo ，永不一个具体的类实现它。

有三种方法可以消除循环依赖：

1. Make MyClass 依赖于 IFoo 而不是 ConcreteFoo 。这可能是最好的选择，如果你能做到这一点。如果问题是您需要在 MyClass 中使用的 IFoo 的实体实例，并且不知道从哪里获取一个来自，然后在构造函数中使用 IFoo ，让谁使用 MyClass 找出什么 IFoo 使用。




2. 将界面移动到自己的程序集中。这仍然是一个相当不错的做法。您的设计将如下所示：

    + Assembly App + Assembly Interfaces + Assembly Concrete 
    | | | 
    | +  - 接口IFoo | 
    | | \ | 
    +  -  MyClass类\ ------ +  -  Class ConcreteFoo 
    | | | ^ 
    + ----会员Foo  - > ---------------------> -------------- ----- | 
    




3. 将 MyClass 移动到自己的程序集中。有效地，您的依赖关系树将与上述＃2看起来一样，但是如果程序集 A 比 B 小得多这将需要较少的努力。

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 ->--------------------->-------------------|
   

3. 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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