用MEF 2构成出口值 [英] Compose exported value with MEF 2

问题描述

使用MEF 1，可以使用ComposeExportedValue（...）-方法（ container.ComposeExportedValue ... ）将现有对象组成容器。如何使用Microsoft.Composition（MEF 2）完成此操作？我找不到用于此目的的任何方法。

With MEF 1 it was possible to compose an existing object to the container with the ComposeExportedValue(...)-Method (container.ComposeExportedValue...). How can this be done with Microsoft.Composition (MEF 2)? I can't find any Method for this purpose.

推荐答案

我将对此进行尝试。当然，在有限地接触MEF 1之后，我自己才学习MEF2。因此，请考虑以下回答，因为这可能是完全错误的。另外，我发现文档非常差且过时，因此到目前为止在各个方面都是艰巨的战斗。

I will have a shot at this one. Granted, I am only about a week in on learning MEF 2 myself, after having some limited exposure to MEF 1. So, please take that in consideration with the following answer as it could be completely wrong. Also, I have found documentation very poor and out of date so it has been an uphill battle in every respect thus far.

在我的解决方案中，我使用了< a href = https://github.com/dotnet/corefx/blob/master/src/System.Composition.Hosting/src/System/Composition/Hosting/Core/ExportDescriptorProvider.cs rel = nofollow> ExportDescriptorProvider 并将其扩展为 InstanceExportDescriptorProvider ，如以下代码所示。

In my solution, I made use of the ExportDescriptorProvider and extended it as an InstanceExportDescriptorProvider as the following code demonstrates.

（请注意，这应被视为概念验证而非最终代码！）

(Please note this should be considered proof-of-concept and not final code!)

public class InstanceExportDescriptorProvider : ExportDescriptorProvider
{
    readonly object instance;

    public InstanceExportDescriptorProvider( object instance )
    {
        this.instance = instance;
    }

    public override IEnumerable<ExportDescriptorPromise> GetExportDescriptors( CompositionContract contract, DependencyAccessor descriptorAccessor )
    {
        if ( contract.ContractType.IsInstanceOfType( instance ) )
        {
            yield return new ExportDescriptorPromise( contract, contract.ContractType.FullName, true, NoDependencies, dependencies => ExportDescriptor.Create( ( context, operation ) => instance, NoMetadata ) );
        }
    }
}

支持测试（使用 xUnit 2.0 与 AutoFixture ），以显示其用法，如下所示：

Supporting test (using xUnit 2.0 paired with AutoFixture) to show how this would be used is as follows:

[Theory, AutoData]
public void VerifyInstanceExport( Assembly[] assemblies )
{
    using ( var container = new ContainerConfiguration()
        .WithProvider( new InstanceExportDescriptorProvider( assemblies ) )
        .CreateContainer() )
    {
        var composed = container.GetExport<Assembly[]>();
        Assert.Equal( assemblies, composed );
    }
}

就我而言，我想访问程序集传递到 ContainerConfiguration （在上面的示例中未看到/未测试），所以这就是为什么我要使用Assemblies进行测试。

In my case I want to have access to the assemblies passed into the ContainerConfiguration (not seen/tested in the above example) so that is why I am testing with Assemblies.

希望这足以让您继续前进。还是某种方式。

Hopefully this will be enough to get you on on your way. Or some way, in any case.

这篇关于用MEF 2构成出口值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！