之间有什么目的MEF和统一不同？ [英] What is different between and purpose of MEF and Unity?

问题描述

我刚开始学习DI（我工作的WPF / Silverlight的，但我有一个计划转移到ASP.NET）。当我阅读网上的一些DI的文章有两个框架，我很感兴趣，MEF与统一。我想知道什么是真正的世界他们之间的不同，哪一个是好去。

I just start study DI (I'm working on WPF/Silverlight but I have a plan to move to ASP.NET). After I read some DI articles from internet there are two Frameworks that I'm interested in, MEF and Unity. I want to know what is the real-world different between them and which one is good to go.

推荐答案

的主要区别是，与统一，你会明确注册要在作文中使用的每个类的：

The main difference is that with unity you will explicitly register each class you want to use in the composition:

var container = new UnityContainer();
container.RegisterType<IFoo,Foo>();
container.RegisterType<IBar,Bar>();
...
var program = container.Resolve<Program>();
program.Run();

在MEF在另一方面，你的属性而不是注册在别的地方纪念类：

In MEF on the other hand, you mark classes with attributes instead of registering them somewhere else:

[Export(typeof(IFoo))]
public Foo
{
   ...
}

乍一看，这看起来像一个小的语法差异，但它实际上是比这更重要。 MEF被设计成允许部件的动态发现。例如，使用 DirectoryCatalog 您可以将应用程序设计以这样一种方式，你可以通过简单的应用程序文件夹下探新的DLL扩展它。

At first sight this looks like a minor syntactic difference, but it is actually more important than that. MEF is designed to allow for the dynamic discovery of parts. For example, with a DirectoryCatalog you can design your application in such a way that you can extend it by simply dropping new DLLs in the application folder.

在这个例子中，MEF会找到并实例化的所有类与 [导出（typeof运算（IPlugin））] 指定目录下的属性，并通过这些实例的计划构造器：

In this example, MEF will find and instantiate all classes with an [Export(typeof(IPlugin))] attribute in the given directory and passes those instances to the Program constructor:

[Export]
public class Program
{
    private readonly IEnumerable<IPlugin> plugins;

    [ImportingConstructor]
    public Program(
       [ImportMany(typeof(IPlugin))] IEnumerable<IPlugin> plugins)
    {
        this.plugins = plugins;
    }

    public void Run()
    {
        // ...
    }
}

切入点：

public static void Main()
{
    using (var catalog = new DirectoryCatalog(".","*"))
    using (var container = new CompositionContainer(catalog))
    {
        var program = container.GetExportedValue<Program>();
        program.Run();
    }
}

要适应这种动态组合方案，MEF有稳定的组合物，一个概念，这意味着当它运行到缺少相关的地方它会简单地标记部分为不可用，并将继续构成反正。

To accommodate such dynamic composition scenarios, MEF has a concept of "stable composition", which means that when it runs into a missing dependency somewhere it will simply mark the part as unavailable and will continue the composition anyway.

<一个href="http://blogs.msdn.com/b/nblumhardt/archive/2009/07/17/light-up-or-mef-optional-exports.aspx">Stable成分是非常有用的，但也使得它很很难调试失败的组成。所以，如果你不需要的部分动态发现和稳定的组合物，我会用一个常规的DI容器，而不是MEF。与MEF，定期DI容器会给你明确的错误信息时，缺少相关。

Stable composition can be quite useful, but it also makes it very difficult to debug a failed composition. So if you don't need dynamic discovery of parts and "stable composition", I would use a regular DI container instead of MEF. Unlike MEF, regular DI containers will give you clear error messages when a dependency is missing.

这也可能可以得到两全其美的使用它集成了MEF，如 DI容器Autofac 的。使用Autofac组成核心应用，和MEF的量需要是动态扩展的部分。

It might also be possible to get the best of both worlds by using a DI container which integrates with MEF, like Autofac. Use Autofac to compose the core application, and MEF for the parts which need to be dynamically extensible.

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