不能在Kephas的开放式通用服务中使用构造函数 [英] Cannot use constructors in open generic services with Kephas
问题描述
以某种方式，我无法使其具有通过构造函数实现的开放通用导出的服务而工作。我试图将[CompositionConstructor]属性添加到它毫无用处。它会抛出类似这样的内容：
Somehow I cannot get to make it work having a service exported as open generic with an implementation with a constructor. I tried to add the [CompositionConstructor] attribute to it to no avail. It throws something like:
System.Composition.Hosting.CompositionFailedException : No importing constructor was found on type 'MyType'.
有什么想法吗？
推荐答案
不幸的是，这是System.Composition库中的错误（请在此处检查 https ：//github.com/dotnet/corefx/issues/40094 ）。如我所见，此错误已添加到5.0里程碑中，意味着明年秋天。从我的角度来看，您有以下选择：
Unfortunately this is a bug in the System.Composition library (check here https://github.com/dotnet/corefx/issues/40094). As I can see, this bug is added to the 5.0 milestone, meaning next year in autumn. From my perspective you have the following options:
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仅将实现类保留为默认构造函数。在这里，您可以使用AmbientServices.Instance.CompositionContainer.GetExport来获取所需的依赖项。我知道这不是最好的解决方案，但应该可以。警告：如果将服务标记为作用域，则如果您依赖其他作用域服务，则将无法获得正确的作用域。
Leave the implementation class only with the default constructor. Here you can use AmbientServices.Instance.CompositionContainer.GetExport to get the dependencies you need. I know it is not the best solution, but it should work. Warning: if the service is marked as scoped, than if you depend on other scoped services you will not get the right scope for them.
Kephas 6.5版。 0带来了Kephas合成的Autofac实现，其中的事物按预期方式工作。在 https://github.com/kephas-software/kephas/releases获取最新版本并构建所需的nuget。我将尝试尽快在nuget上发布beta版本。
Kephas version 6.5.0 brings an Autofac implementation for Kephas composition, where the things work as they suppose to be. Check the sources at https://github.com/kephas-software/kephas/releases to get the latest version and build the nugets you need. I will try to publish a beta version on nuget soon.
为您使用的版本带来自己的组合实现，并选择DI容器。您可以将Autofac实现作为参考，尽管最新版本中有一些重大更改。选择DI容器时，请确保它支持开放的泛型，元数据以及支持IExportFactory接口的方法。
Bring your own implementation of composition for the version you use, with your DI container of choice. You could take as reference the Autofac implementation, although there are a couple of breaking changes in the latest version. When choosing a DI container, make sure it supports open generics, metadata, and a way to support the IExportFactory interfaces.
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