ASP.NET MVC ContactsManager 教程中是否有解决依赖注入循环问题的好/正确方法? [英] Is there a good/proper way of solving the dependency injection loop problem in the ASP.NET MVC ContactsManager tutorial?

问题描述

如果你不知道我在说什么，要么通过 教程并尝试自己添加依赖注入，或者试试我对问题的解释.

注意:这个问题不在 ASP.NET 原始教程的范围内.本教程仅建议使用的模式对依赖注入友好.

问题基本上是 Controller、ModelStateWrapper 和 ContactManagerService 之间存在依赖循环.

1. ContactController 构造函数采用 IContactManagerService.
2. ContactManagerService 构造函数采用 IContactManagerRepository (不重要) 和 IValidationDictionary (ModelStateWrapper 实现).
3. ModelStateWrapper 构造函数采用 ModelStateDictionary (这是控制器上名为ModelState"的属性).

所以依赖循环是这样的:Controller > Service > ModelStateWrapper > Controller

如果您尝试向其添加依赖注入，它将失败.所以我的问题是；我该怎么办?其他人已经发布了这个问题，但答案很少，而且各不相同，而且似乎都有些hack-ish".

我当前的解决方案是从 IService 构造函数中删除 IModelStateWrapper 并添加一个 Initialize 方法，如下所示:

public class ContactController : 控制器{私有只读 IContactService _contactService;公共联系控制器(IContactService 联系服务){_contactService = 联系服务；contactService.Initialize(new ModelStateWrapper(ModelState));}//类实现...}公共类 ContactService : IContactService{私人 IValidationDictionary _validationDictionary;私有只读 IContactRepository _contactRepository;公共联系服务(IContactRepository contactRepository){_contactRepository = contactRepository;}私有无效初始化(IValidationDictionary validationDictionary){if(validationDictionary == null)throw new ArgumentNullException("validationDictionary");_validationDictionary = 验证字典；}//类实现...}公共类 ModelStateWrapper : IValidationDictionary{私有只读 ModelStateDictionary _modelState;公共 ModelStateWrapper(ModelStateDictionary modelState){_modelState = 模型状态；}//类实现...}

通过这个构造，我可以像这样配置我的统一容器:

public static void ConfigureUnityContainer(){IUnityContainer 容器 = 新的 UnityContainer();//注册container.RegisterTypeInHttpRequestLifetime();container.RegisterTypeInHttpRequestLifetime();ControllerBuilder.Current.SetControllerFactory(new UnityControllerFactory(container));}

不幸的是，这意味着必须由控制器构造函数手动调用服务上的Initialize"方法.有没有更好的办法?也许我以某种方式将 IValidationDictionary 包含在我的统一配置中?我应该切换到另一个 DI 容器吗?我错过了什么吗?

解决方案

作为一般考虑，循环依赖表明设计缺陷 - 我想我可以放心地说，因为您不是代码的原始作者:)

我不认为 Initialize 方法是一个好的解决方案.除非您正在处理加载项场景(您不是)，否则方法注入不是正确的解决方案.您几乎已经想通了，因为您发现需要手动调用它并不令人满意，因为您的 DI Container 不能.

除非我完全弄错了，否则 ContactController 在其 Action 方法被调用之前不需要 IValidationDictionary 实例?

如果这是真的，最简单的解决方案可能是定义 IValidationDictionaryFactory 接口并使 ContactController 构造函数采用该接口的实例.

这个接口可以这样定义:

公共接口 IValidationDictionaryFactory{IValidationDictionary 创建(控制器控制器)；}

控制器上任何需要 IValidationDictionary 实例的 Action 方法都可以调用 Create 方法来获取实例.

默认实现如下所示:

公共类 DefaultValidationDictionaryFactory : IValidationDictionaryFactory{公共 IValidationDictionary 创建(控制器控制器){返回控制器.ModelState;}}

If you don't know what I'm talking about either go through the tutorial and try to add dependency Injection yourself or try your luck with my explanation of the problem.

Note: This problem isn't within the scope of the original tutorial on ASP.NET. The tutorial only suggests that the patterns used are dependency injection friendly.

The problem is basically that there is a dependency loop between the Controller, the ModelStateWrapper and the ContactManagerService.

1. The ContactController constuctor takes an IContactManagerService.
2. The ContactManagerService constructor takes an IContactManagerRepository (not important) and an IValidationDictionary (which ModelStateWrapper implements).
3. The ModelStateWrapper constructor takes a ModelStateDictionary (which is a property called "ModelState" on the controller).

So the dependency cycle goes like this: Controller > Service > ModelStateWrapper > Controller

If you try to add dependency injection to this, it will fail. So my question is; what should I do about it? Others have posted this question, but the answers are few, different, and all seem kinda "hack-ish".

My current solution is to remove the IModelStateWrapper from the IService constructor and add an Initialize method instead like this:

public class ContactController : Controller
{
    private readonly IContactService _contactService;

    public ContactController(IContactService contactService)
    {
        _contactService = contactService;
        contactService.Initialize(new ModelStateWrapper(ModelState));
    }

    //Class implementation...
}

public class ContactService : IContactService
{
    private IValidationDictionary _validationDictionary;
    private readonly IContactRepository _contactRepository;

    public ContactService(IContactRepository contactRepository)
    {
        _contactRepository = contactRepository;
    }

    private void Initialize(IValidationDictionary validationDictionary)
    {
        if(validationDictionary == null)
            throw new ArgumentNullException("validationDictionary");

        _validationDictionary = validationDictionary;
    }

    //Class implementation...
}

public class ModelStateWrapper : IValidationDictionary
{
    private readonly ModelStateDictionary _modelState;

    public ModelStateWrapper(ModelStateDictionary modelState)
    {
        _modelState = modelState;
    }

    //Class implementation...
}

With this construct I can configure my unity container like this:

public static void ConfigureUnityContainer()
{
    IUnityContainer container = new UnityContainer();

    // Registrations
    container.RegisterTypeInHttpRequestLifetime<IContactRepository, EntityContactRepository>();
    container.RegisterTypeInHttpRequestLifetime<IContactService, ContactService>();

    ControllerBuilder.Current.SetControllerFactory(new UnityControllerFactory(container));
}

Unfortunately this means that the "Initialize" method on the service has to be called manually by the controller constructor. Is there a better way? Maybe where I somehow include the IValidationDictionary in my unity configuration? Should I switch to another DI container? Am I missing something?

解决方案

As a general consideration, circular dependencies indicate a design flaw - I think I can safely say this since you are not the original author of the code :)

I wouldn't consider an Initialize method a good solution. Unless you are dealing with an add-in scenario (which you aren't), Method Injection is not the right solution. You have almost already figured that out, since you find it unsatisfactory that you need to manually invoke it because your DI Container can't.

Unless I am entirely mistaken, the ContactController doesn't need the IValidationDictionary instance before its Action methods are being invoked?

If this is true, the easiest solution would probably be to define an IValidationDictionaryFactory interface and make the ContactController constructor take an instance of this interface.

This interface could be defined like this:

public interface IValidationDictionaryFactory
{
    IValidationDictionary Create(Controller controller);
}

Any Action method on the controller that needs an IValidationDictionary instance can then invoke the Create method to get the instance.

The default implementation would look something like this:

public class DefaultValidationDictionaryFactory : IValidationDictionaryFactory
{
    public IValidationDictionary Create(Controller controller)
    {
        return controller.ModelState;
    }
}

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