将自定义依赖项解析器与 Unity 和 Web API 控制器一起使用时出错

Question

我正在使用以下 class 作为依赖项解析器。从 http://www.asp.net/web-api/overview/advanced/dependency-injection

获得参考

   public class UnityWebAPIResolver : IDependencyResolver
    {
    protected IUnityContainer container;

    public UnityWebAPIResolver(IUnityContainer container)
    {
        if (container == null)
        {
            throw new ArgumentNullException("container");
        }
        this.container = container;
    }

    public object GetService(Type serviceType)
    {
        try
        {
            return container.Resolve(serviceType); **// This line throws error**
        }
        catch (ResolutionFailedException)
        {
            return null;
        }
    }

    public IEnumerable<object> GetServices(Type serviceType)
    {
        try
        {
            return container.ResolveAll(serviceType); **// This line throws error**
        }
        catch (ResolutionFailedException)
        {
            return new List<object>();
        }
    }

    public IDependencyScope BeginScope()
    {
        var child = container.CreateChildContainer();
        return new UnityWebAPIResolver(child);
    }

    public void Dispose()
    {
        container.Dispose();
    }
}

在路由配置后的 WebApiConfig class 中，我正在像这样配置依赖解析器

config.DependencyResolver = new UnityWebAPIResolver(UnityConfig.GetContainer());

问题是我遇到了几个这样的错误..

InvalidOperationException - The type IHostBufferPolicySelector does not have an accessible constructor.
InvalidOperationException - The type ModelMetadataProvider does not have an accessible constructor.
InvalidOperationException - The type ITraceManager does not have an accessible constructor.
InvalidOperationException - The type ITraceWriter does not have an accessible constructor.
InvalidOperationException - The type IHttpControllerSelector does not have an accessible constructor.
InvalidOperationException - The type IAssembliesResolver does not have an accessible constructor.
InvalidOperationException - The type IHttpControllerTypeResolver does not have an accessible constructor.
InvalidOperationException - The type IHttpActionSelector does not have an accessible constructor.
InvalidOperationException - The type IActionValueBinder does not have an accessible constructor.
InvalidOperationException - The type IContentNegotiator does not have an accessible constructor.
InvalidOperationException - The type IHttpControllerActivator does not have an accessible constructor.
InvalidOperationException - The type IBodyModelValidator does not have an accessible constructor.

即使我尝试在 global.asax 中做这样的事情，我也会遇到同样的错误。

GlobalConfiguration.Configuration.DependencyResolver = new UnityWebAPIResolver(UnityConfig.GetContainer());

问题：我的 API 控制器中的所有依赖项似乎都已正确注入，我唯一担心的是因为它不能解决上面提到的几个 （框架特定） 类型，它是否有可能导致整个框架故障并产生随机错误？

Answer 1

没有问题，您的程序在这里按预期运行。您看到的是 Unity 的 Resolve 方法抛出的第一次机会异常。抛出异常是因为当无法解析服务时，Unity 永远不会 return null。 IDependencyResolver.GetService 然而，如果请求的服务未在依赖解析器实现中注册，则实现应始终 return null。

如果 GetService returns null，MVC 将回退到框架对所请求服务的默认实现。在大多数情况下，不需要在 Unity 容器中重写这些服务，即使需要不同的服务，您也可以轻松替换 MVC 的默认实现，而无需将其添加到 Unity 配置中。

但由于 Unity 预计会抛出此异常，因此这些方法包含 catch 子句。因此，您遇到的异常是在该方法中捕获的，并且 null 是 returned.

显然启动应用程序后调试器多次停在那些方法上是很烦人的，所以解决办法是用[DebuggerStepThrough]属性标记这些方法，以防止调试器停在这些方法。

将自定义依赖项解析器与 Unity 和 Web API 控制器一起使用时出错

Errors while using custom dependency resolver with Unity and Web API controller

c#

asp.net-web-api

unity-container