2

我正在使用来自Codeplex 主页的最新 MEF 2 预览版，它应该添加开放泛型支持。确实如此，但在这种特定情况下，MEF 无法组合通用接口的通用实现：

public interface IOuter
{
    IInner Value { get; }
}

[Export(typeof(IOuter))]
public class MyOuter : IOuter
{
    [ImportingConstructor]
    public MyOuter(InnerGenericClass<string, int> value)
    {
        this.Value = value;
    }

    public IInner Value { get; private set; }
}

public interface IInner
{
    void Say();
}
public interface IGenericInner<T, K> : IInner
{
    // something else here
}

[Export(typeof(IGenericInner<,>))]
public class InnerGenericClass<T, K> : IGenericInner<T, K>
{
    public void Say()
    {
        Console.WriteLine("{0}, {1}", typeof(T), typeof(K));
    }
}

class Startup
{
    public void CatalogSetup()
    {
        var catalog = new AggregateCatalog(
            new AssemblyCatalog(Assembly.GetExecutingAssembly())
            );
        var container = new CompositionContainer(catalog, CompositionOptions.DisableSilentRejection);

        var batch = new CompositionBatch();

        container.Compose(batch);

        var outer = container.GetExportedValue<IOuter>();
        outer.Value.Say();
    }
}

这是CompositionExpect：

The composition produced a single composition error. The root cause is provided below. Review the CompositionException.Errors property for more detailed information.

1) No exports were found that match the constraint: 
    ContractName    ConsoleApplication1.InnerGenericClass(System.String,System.Int32)
    RequiredTypeIdentity    ConsoleApplication1.InnerGenericClass(System.String,System.Int32)

Resulting in: Cannot set import 'ConsoleApplication1.MyOuter.Value (ContractName="ConsoleApplication1.InnerGenericClass(System.String,System.Int32)")' on part 'ConsoleApplication1.MyOuter'.
Element: ConsoleApplication1.MyOuter.Value (ContractName="ConsoleApplication1.InnerGenericClass(System.String,System.Int32)") -->  ConsoleApplication1.MyOuter -->  AssemblyCatalog (Assembly="ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")

Resulting in: Cannot get export 'ConsoleApplication1.MyOuter (ContractName="ConsoleApplication1.IOuter")' from part 'ConsoleApplication1.MyOuter'.
Element: ConsoleApplication1.MyOuter (ContractName="ConsoleApplication1.IOuter") -->  ConsoleApplication1.MyOuter -->  AssemblyCatalog (Assembly="ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null")

即使我将 InnerGenericClass 的导入移动到MyOuter.Value的属性，也会引发相同的异常：

[Export(typeof(IOuter))]
public class MyOuter : IOuter
{
    [Import(typeof(InnerGenericClass<string, int>))]
    public IInner Value { get; private set; }
}

奇怪的是，当我将导入类型更改为IGenericInner时，它确实有效：

[Export(typeof(IOuter))]
public class MyOuter : IOuter
{
    [ImportingConstructor]
    public MyOuter(IGenericInner<string, int> value)
    {
        this.Value = value;
    }

    public IInner Value { get; private set; }
}

更奇怪的是，通过属性导入时它不起作用。

摘要：我不能使用泛型接口将对象导入到Value属性，因为IGenericInner接口可能有更多的实现（我也想导入一个特定的实现，但这并不重要）。

我希望在这种情况下我不必完全绕过 MEF。

4

1 回答 1

5

导致您导出接口 IGenericInner<> 但要导入特定类 InnerGenericClass MEF 找不到正确的部分。您可以通过这种方式导出和导入特定类或创建两个 InnerGenericClass<> 导出：

[Export(typeof(IGenericInner<,>))]
[Export(typeof(InnerGenericClass<,>))]
public class InnerGenericClass<T, K> : IGenericInner<T, K> {
    public void Say() {
        Console.WriteLine("{0}, {1}", typeof(T), typeof(K));
    }
}

我刚刚在 VS .NET 4.5 项目中对此进行了测试，它可以工作。顺便提一句。MEF 2 已在 .NET 4.5 中发布 - 如果可能，我建议使用框架的 System.ComponentModel.Composition.dll 部分而不是预览版。

更新：第三种解决方案（适用于预览版 5）可能是另外使用字符串合同名称。我个人尽量避免这种难看语法的原因，但没关系。代码将如下所示：

[Export(typeof(IOuter))]
public class MyOuter : IOuter {
    [ImportingConstructor]
    public MyOuter([Import("MySpecialInnerGenericClass", typeof(IGenericInner<,>))]InnerGenericClass<string, int> value) {
        this.Value = value;
    }

    public IInner Value { get; private set; }
}
[Export("MySpecialInnerGenericClass", typeof(IGenericInner<,>))]
public class InnerGenericClass<T, K> : IGenericInner<T, K> {
    public void Say() {
        Console.WriteLine("{0}, {1}", typeof(T), typeof(K));
    }
}
于 2013-02-20T08:54:22.763 回答