难以让 Unity 依赖注入与 WebAPI 和 OWIN 一起使用答案

【问题标题】：Difficulty getting Unity dependency injection working with WebAPI, and OWIN难以让 Unity 依赖注入与 WebAPI 和 OWIN 一起使用
【发布时间】：2016-08-19 18:14:33
【问题描述】：

当我尝试在我的应用程序上调用控制器 API 端点时，我收到此错误：

   {
  "Message": "An error has occurred.",
  "ExceptionMessage": "An error occurred when trying to create a controller of type 'ProviderController'. Make sure that the controller has a parameterless public constructor.",
  "ExceptionType": "System.InvalidOperationException",
  "StackTrace": "   at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)\r\n   at System.Web.Http.Controllers.HttpControllerDescriptor.CreateController(HttpRequestMessage request)\r\n   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()",
  "InnerException": {
    "Message": "An error has occurred.",
    "ExceptionMessage": "Type 'mynamespace.api.controllers.ProviderController' does not have a default constructor",
    "ExceptionType": "System.ArgumentException",
    "StackTrace": "   at System.Linq.Expressions.Expression.New(Type type)\r\n   at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, Func`1& activator)\r\n   at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)"
  }
}

我的配置如下，我使用的是Unity.WebAPI库：

Startup.cs

    public void Configuration(IAppBuilder app)
    {
        HttpConfiguration config = GlobalConfiguration.Configuration;
        config.DependencyResolver = new UnityDependencyResolver(UnityConfig.GetConfiguredContainer());
        app.UseWebApi(WebApiConfig.Register());
        app.UseCors(CorsOptions.AllowAll);


        config.EnsureInitialized();

    }

UnityConfig.cs：

public static class UnityConfig
{
    #region Unity Container

    /// <summary>
    /// Load types in Unity Container 
    /// </summary>
    private static Lazy<IUnityContainer> container = new Lazy<IUnityContainer>(() =>
    {
        var container = new UnityContainer();
        RegisterTypes(container);
        return container;
    });

    /// <summary>
    /// Gets the configured Unity container.
    /// </summary>
    public static IUnityContainer GetConfiguredContainer()
    {
        return container.Value;
    }

    #endregion


    /// <summary>
    /// Register the types into Unity Container.
    /// </summary>
    /// <param name="container"></param>
    public static void RegisterTypes(UnityContainer container)
    {
        container.RegisterType<IProviderService, ProviderService();  
    } 
}

ProviderController.cs：

public class ProviderController : ApiController
{
    private static readonly ILog log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
    private readonly IProviderService providerService;      

    public ProviderController(IProviderService providerService)
    {
        providerService = providerService;
    }

    //Controller API Methods
}

ProviderService.cs：

    public ProviderService()
    {
        this.serviceClient = new ServiceClientAdapter();
    }

我整个上午都在阅读各种线程，但无法弄清楚我哪里出错了。如果我删除 Unity 并直接在控制器中实例化一个新的 ProviderService，一切正常。

【问题讨论】：

标签： c# asp.net-web-api2 unity-container owin

【解决方案1】：

我的问题是一个小小的疏忽。 Startup.cs 中对 UseWebApi 的调用没有将 HttpConfiguration 配置对象作为参数，而是声明它是自己的。这意味着 WebAPI 和 Unity 配置了不同的 HTTPConfiguration 对象，因此 WebAPI 不知道 Unity。

【讨论】：

我想我可能有类似的问题。我尝试从启动类向 DependencyResolver 注入配置对象，但没有成功！你是怎么解决的？
如果你看我上面的例子，对于 Startup.cs，第一行的 config 对象用于配置 Unity。然后当调用 app.UseWebApi 时，会创建一个新的配置对象并将其传递给它。这就是问题所在，应该传入第一行声明的配置。
谢谢兄弟！它有帮助。

【解决方案2】：

答案已经有了！只是为了方便或更短的代码。

你可以写一个方法

    public static void RegisterComponents()
    {
        var container = new UnityContainer();

        // register all your components with the container here
        // it is NOT necessary to register your controllers

        container.RegisterType<IProviderService, ProviderService>();

        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }

Startup.cs：

    public void Configuration(IAppBuilder app)
    {
        ConfigureOAuth(app);
        HttpConfiguration config = GlobalConfiguration.Configuration;
        app.UseWebApi(config);
    }

然后添加 UnityConfig.RegisterComponents();进入全局文件

【讨论】：