依赖注入问题（双向通信） [英] Dependency injection issue (bidirectional communication)

问题描述

我有 a 个 A 和 b B

a 的实例必须能够要在 b 和 b 上调用方法，则必须立即在 a上调用方法如果某些检查通过。

a must be able to call a method on b and b must then immediatly call a method on a if some checks pass.

要实现这一点，我将使用循环DI

To achieve this I would have cyclic DI

public A(B b) { _b = b; }
public void CallToB() { _b.Method(); }
public void Method() { DoSomething(); }

public B(A a) { _a = a; }
public void Method() { if (SomeCheck()) _a.Method(); }

我知道我可以通过使用事件让 b 不知道/独立于 a 。

I know I could get arround this, using events and let b be unaware/independant of a. But it would feel wrong.

注意：在实现双向通讯的情况下，我没有看到这个问题的答案。

Note: I haven't seen an answer to this question where bidirectional communication was made possible.

推荐答案

您可以通过依赖接口而不是具体类型来解决此问题，然后使用属性注入。下面是一个示例：

You can solve this issue by depending on interfaces instead of concrete types and then use property injection. Here is an example:

public interface IA
{
    void Method();
}

public class A : IA
{
    private readonly IB _b;
    public A(IB b){_b = b;}
    //...
}

public interface IB
{
    void Method();
}

public class B : IB
{
    private readonly IA _a;
    public B(IA a){_a = a;}
    //...
}

public class BCycleDependencyBreaker : IB
{
    private IB _b;

    public IB b
    {
        set { _b = value; }
    }

    public void Method()
    {
        _b.Method();
    }
}

然后使用 BCycleDependencyBreaker ，例如：

var b_cycle_dependency_breaker = new BCycleDependencyBreaker();

//Make a depend on this implementation of b that currently does nothing
A a = new A(b_cycle_dependency_breaker); 

//Make b depend on a
B b = new B(a);

//Now, let the proxy implementation delegate calls to the real b
b_cycle_dependency_breaker.b = b;

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