如何将多个演示者注入主演示者？答案

【问题标题】：How to inject multiple presenters into the main presenter?如何将多个演示者注入主演示者？
【发布时间】：2014-11-20 22:12:07
【问题描述】：

根据answer，我可以将依赖项注入构造函数。但是，如果假设我有 10 个“子演示者”怎么办？我应该通过构造函数注入所有这些吗？对于这种情况，推荐使用什么设计模式（工厂方法、外观等）？如果您能提供示例代码以使用 NUnit 和 NSubstitute 对其进行测试，我将不胜感激？提前致谢！

public void PresenterMain(IViewMain view
, IServiceMain service
, IAddNewJobPresenter addNewJobPresenter
, IClientManagementPresenter clientManagementPresenter
, IJobBatchesPresenter jobBatchesPresenter
, IReportsPresenter reportPresenter...etc)

【问题讨论】：

如果您的IPresenter 对象是在编译时组合的，然后通过Constructor injection 传递它们，您应该尽可能争取Constructor injection。您可以通过您的 IoC 容器为您的构造函数提供 IEnumerable<T> where T : IPresenter，或者如果您不使用一个可怜的 mans DI。

标签： c# design-patterns dependency-injection mvp

【解决方案1】：

鉴于您的消费者需要使用 10 个演示者实例，有几个选项。以下是设置场景的一些基本框架：

public interface IPresenter
{
    void Present();
}

public interface IConsumer
{
    void DoSomething();
}

public class SomeConsumer : IConsumer
{
    private readonly IPresenter presenter;

    public SomeConsumer(IPresenter presenter)
    {
        if (presenter == null)
            throw new ArgumentNullException("presenter");
        this.presenter = presenter;
    }

    public void DoSomething()
    {
        this.presenter.Present();
    }
}

您可以使用composite pattern，然后您可以在列表中对演示者进行排序。

public class Presenter1 : IPresenter
{
    public void Present()
    {
        // Do something here
    }
}

public class Presenter2 : IPresenter
{
    public void Present()
    {
        // Do something here
    }
}

public class Presenter3 : IPresenter
{
    public void Present()
    {
        // Do something here
    }
}

public class CompositePresenter : IPresenter
{
    private readonly IPresenter[] presenters;

    public CompositePresenter(IPresenter[] presenters)
    {
        if (presenters == null)
            throw new ArgumentNullException("presenters");
        this.presenters = presenters;
    }

    public void Present()
    {
        // Do nothing except delegate the call to the nested
        // instances. You may need to do some extra work to deal
        // with multiple return values, like add up the values
        // or decide which value works best for the scenario.
        foreach (var presenter in this.presenters)
        {
            presenter.Present();
        }
    }
}

然后像这样连接起来：

var presenter1 = new Presenter1();
var presenter2 = new Presenter2();
var presenter3 = new Presenter3();
var compositePresenter = new CompositePresenter(new IPresenter[] {
    presenter1,
    presenter2,
    presenter3
});

var consumer = new SomeConsumer(compositePresenter);

或者你可以使用decorator pattern:

public class Presenter1 : IPresenter
{
    public Presenter1(IPresenter innerPresenter)
    {
        if (innerPresenter == null)
            throw new ArgumentNullException("innerPresenter");
        this.innerPresenter = innerPresenter;
    }

    public void Present()
    {
        // Do something here

        // You could make this call conditional
        this.innerPresenter.Present();

        // Or do something here
    }
}

public class Presenter2 : IPresenter
{
    public Presenter2(IPresenter innerPresenter)
    {
        if (innerPresenter == null)
            throw new ArgumentNullException("innerPresenter");
        this.innerPresenter = innerPresenter;
    }

    public void Present()
    {
        // Do something here

        // You could make this call conditional
        this.innerPresenter.Present();

        // Or do something here
    }
}

public class Presenter3 : IPresenter
{
    public Presenter3(IPresenter innerPresenter)
    {
        if (innerPresenter == null)
            throw new ArgumentNullException("innerPresenter");
        this.innerPresenter = innerPresenter;
    }

    public void Present()
    {
        // Do something here

        // You could make this call conditional
        this.innerPresenter.Present();

        // Or do something here
    }
}

public class NullPresenter : IPresenter
{
    public void Present()
    {
        // Do nothing here - this class is a placeholder
        // in case you want to expand the design later
    }
}

然后像这样连接起来：

var nullPresenter = new NullPresenter();
var presenter3 = new Presenter3(nullPresenter);
var presenter2 = new Presenter2(presenter3);
var presenter1 = new Presenter1(presenter2);

var consumer = new SomeConsumer(presenter1);

【讨论】：