Question

我正在开发一个WPF应用程序，它具有很大的业务逻辑和数据处理能力。根据使用IoC的想法，我决定将Ninject用作这部分逻辑和数据处理的依赖注入器。

我初始化了ninject的内核，并使用App.xaml.cs文件中的具体类（即默认的app类）绑定了接口。到目前为止一切都很好。

问题是在我的应用程序的某个地方我需要一个类的两个具体实例（我不想在构造函数中作为参数传递）。其实我需要做的是：

var instance1 = kernel.Get<IClassName>();

问题是我无法访问kernel（Ninject内核的具体实例）。

我知道在ASP.NET MVC中我可以做类似

的事情

var instance1 = (IClassName)System.Web.Mvc.DependencyResolver.Current.GetService(typeof(IClassName));

我可以使用类似的东西吗？或者我是否被迫用服务定位器模式来解决问题（我知道存在相互矛盾的意见）？

Answer 1

由于您希望每个类使用多个依赖项，因此您应该设计模式而不是DI容器来解决您的问题。

至少有几种选择。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订阅演示者。

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();
        }
    }
}

然后将它连接起来：

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);

在Ninject中，上面的内容如下：

var kernel = new StandardKernel();
kernel.Bind<Presenter1>().ToSelf();
kernel.Bind<Presenter2>().ToSelf();
kernel.Bind<Presenter3>().ToSelf();
kernel.Bind<IPresenter>().To<CompositePresenter>()
    .WithConstructorArgument("presenters", 
        new IPresenter[] { 
            kernel.Get<Presenter1>(), 
            kernel.Get<Presenter2>(),
            kernel.Get<Presenter3>() 
        });

// When SomeConsumer is injected into a constructor, its IPresenter 
// dependency will be wired as shown with the new keyword example above.

或者您可以使用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
    }
}

然后将它连接起来：

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

var consumer = new SomeConsumer(presenter1);

在Ninject中，上面的内容如下：

var kernel = new StandardKernel();
kernel.Bind<IPresenter>().To<NullPrenter>().WhenInjectedInto<Presenter3>();
kernel.Bind<IPresenter>().To<Presenter3>().WhenInjectedInto<Presenter2>();
kernel.Bind<IPresenter>().To<Presenter2>().WhenInjectedInto<Presenter1>();
kernel.Bind<IPresenter>().To<Presenter1>();

// When SomeConsumer is injected into a constructor, its IPresenter 
// dependency will be wired as shown with the new keyword example above.

使用设计模式的优势在于您最终得到的松散耦合代码完全模块化，可扩展，甚至独立于DI容器。

Answer 2

如何使用Ninject.Extensions.Factory来实例化所述依赖项？您可以注入Func<T>，当您稍后调用它时，它将返回一个新实例化的T。还有Lazy<T>以防你想要在第一次使用＆＃34;后期实例化单个实例＆＃34;

然后，您还可以定义接口工厂，如：

public interface IFooFactory
{
    IFoo Create();
}

带有相应的绑定：

Bind<IFooFactory>().ToFactory();
Bind<IFoo>().To<Foo>(); // add Singleton, or ToMethod binding,.. or whatever you require

WPF应用程序中的Ninject：请求类型的实例

2 个答案: