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Circular Dependency in constructors and Dependency Injection

Thursday, July 31, 2008
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Labels: Misko Hevery

9 comments :

  1. AnonymousAugust 1, 2008 at 12:20:00 PM PDT

    Could you post a small example?

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  2. DavidAugust 1, 2008 at 1:01:00 PM PDT

    What about circular references involving several classes. How do you apply your rule in these (more typical) cases?

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  3. assmanAugust 1, 2008 at 1:50:00 PM PDT

    I would really like to see an example too. It seems to me that the shorter of the two lists of methods is just going to be either class A or class B itself.

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  4. assmanAugust 1, 2008 at 1:56:00 PM PDT

    Is it supposed to be a list of methods in the class that reference the other object?

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  5. Michael LeeAugust 2, 2008 at 1:36:00 PM PDT

    Can I just AOL the example request. I'm a little confused by what you mean by this.

    Also why would this be any harder to test than any other complex required dependency? Mock or stub the injected instance.

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  6. UnknownAugust 4, 2008 at 11:24:00 AM PDT

    Really enjoying your posts Miško, each one makes me think :)

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  7. UnknownAugust 5, 2008 at 6:58:00 AM PDT

    I've reached this from a different direction; when I've had a difficult service to test, I've split it into two cooperating services that can each be tested on their own.

    HiveMind and T5 IoC are capable of co-injecting (via constructors) services; this is because what gets injected is a proxy. You'd have a problem trying to inject service implementation A into service implemenation B and vice versa at the same time, but with proxies, theres the extra abstraction.

    Anyway, the mantra is: "Small is Beautiful".

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  8. TorgnyAugust 5, 2008 at 1:28:00 PM PDT

    An example of this (that I used on my blog):
    Circular dependencies between classes can be solved by introducing a new class, e.g., if classes 'Alice' and 'Bob' has references to each other for exchanging messages, then a class 'Channel' should be introduced that they both will use to send and receive messages.

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  9. AnonymousAugust 4, 2009 at 12:12:00 PM PDT

    Hi Misko,
    What kind of class would you make to resolve the circular dependency introduced by applying DI to the MVP pattern? Currently I'm manually injecting the view, inside the view's ctor, into a 'View' property in the presenter, which is ugly. Now I have to remember every time I make a new implementation of this view to set the presenter's View property. I could use a DI framework to automatically inject the property--assuming I set the View implementation to be a singleton in binding configuration (else it would try to inject a brand new view, which puts me right back where I started). There's got to be a better way, though. Maybe a better View-Presenter design?

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