Question

我正在使用Web.api和Unity，我在尝试打开默认的“帮助”区域时收到以下错误：

[InvalidOperationException: The type String cannot be constructed. You must configure the      container to supply this value.]
Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy.GuardTypeIsNonPrimitive(IBuilderContext context, SelectedConstructor selectedConstructor) +280
Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy.PreBuildUp(IBuilderContext context) +356
   Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context) +260
   Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlanCreatorPolicy.CreatePlan(IBuilderContext context, NamedTypeBuildKey buildKey) +205
   Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context) +231
   Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context) +260
   Microsoft.Practices.ObjectBuilder2.BuilderContext.NewBuildUp(NamedTypeBuildKey newBuildKey) +250
   Microsoft.Practices.Unity.ObjectBuilder.NamedTypeDependencyResolverPolicy.Resolve(IBuilderContext context) +101
   BuildUp_System.Web.Http.HttpRouteCollection(IBuilderContext ) +202
   Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context) +42
   Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context) +319
   Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context) +260
   Microsoft.Practices.ObjectBuilder2.BuilderContext.NewBuildUp(NamedTypeBuildKey newBuildKey) +250
   Microsoft.Practices.Unity.ObjectBuilder.NamedTypeDependencyResolverPolicy.Resolve(IBuilderContext context) +101
   BuildUp_System.Web.Http.HttpConfiguration(IBuilderContext ) +202
   Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context) +42
   Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context) +319
   Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context) +260
   Microsoft.Practices.ObjectBuilder2.BuilderContext.NewBuildUp(NamedTypeBuildKey newBuildKey) +250
   Microsoft.Practices.Unity.ObjectBuilder.NamedTypeDependencyResolverPolicy.Resolve(IBuilderContext context) +101
   BuildUp_API.Areas.HelpPage.Controllers.HelpController(IBuilderContext ) +204
   Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context) +42
   Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context) +319
   Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context) +260
   Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable`1 resolverOverrides) +373


[ResolutionFailedException: Resolution of the dependency failed, type = "API.Areas.HelpPage.Controllers.HelpController", name = "(none)".
Exception occurred while: while resolving.
Exception is: InvalidOperationException - The type String cannot be constructed. You must configure the container to supply this value.
-----------------------------------------------
At the time of the exception, the container was:

   Resolving API.Areas.HelpPage.Controllers.HelpController,(none)
  Resolving parameter "config" of constructor API.Areas.HelpPage.Controllers.HelpController(System.Web.Http.HttpConfiguration config)
Resolving System.Web.Http.HttpConfiguration,(none)
Resolving parameter "routes" of constructor System.Web.Http.HttpConfiguration(System.Web.Http.HttpRouteCollection routes)
  Resolving System.Web.Http.HttpRouteCollection,(none)
  Resolving parameter "virtualPathRoot" of constructor System.Web.Http.HttpRouteCollection(System.String virtualPathRoot)
    Resolving System.String,(none)
]
   Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable`1 resolverOverrides) +436
   Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, String name, IEnumerable`1  resolverOverrides) +50
   Microsoft.Practices.Unity.UnityContainer.Resolve(Type t, String name, ResolverOverride[] resolverOverrides) +48
   Microsoft.Practices.Unity.UnityContainerExtensions.Resolve(IUnityContainer container, Type t, ResolverOverride[] overrides) +61
   Unity.Mvc4.UnityDependencyResolver.GetService(Type serviceType) +140
   System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +87

[InvalidOperationException: An error occurred when trying to create a controller of type     'API.Areas.HelpPage.Controllers.HelpController'. Make sure that the controller has a parameterless    public constructor.]
   System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +247
   System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +438
   System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +226
   System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +326
   System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +177
   System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +88
    System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +50
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +301
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

我是团结的新手，我确信我错过了一步。在webapiconfig.cs中：

public static void Register(HttpConfiguration config)
{
    config.Routes.MapHttpRoute(
    name: "DefaultApi",
    routeTemplate: "api/{controller}/{action}/{id}",
    defaults: new { id = RouteParameter.Optional }
    );

    //Custom formatter
    config.Formatters.Clear();
    config.Formatters.Add(new JSONPFormater());

    config.EnableSystemDiagnosticsTracing();

    //Setup DI
    Bootstrapper.Initialise();
}

Bootstraper.cs（默认值）

public static class Bootstrapper
  {
    public static IUnityContainer Initialise()
    {
      var container = BuildUnityContainer();

      DependencyResolver.SetResolver(new UnityDependencyResolver(container));

      return container;
    }

    private static IUnityContainer BuildUnityContainer()
    {
      var container = new UnityContainer();

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

      // e.g. container.RegisterType<ITestService, TestService>();    
      RegisterTypes(container);

      return container;
    }

    public static void RegisterTypes(IUnityContainer container)
    {

    }
  }

我尝试使用web.config 的web.config

 <configSections>
    <!-- For more information on Entity Framework configuration, visit        http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework"     type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    <section name="unity"  type="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection, Microsoft.Practices.Unity.Configuration"/>
  </configSections>
  <connectionStrings>
    <add name="DefaultConnection" providerName="System.Data.SqlClient" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=aspnet-API-20130708152001;Integrated     Security=SSPI;AttachDBFilename=|DataDirectory|\aspnet-API-20130708152001.mdf" />
    <add name="<REMOVED>DBEntities" connectionString="metadata=res://*/Models.DAL.<REMOVED>.csdl|res://*/Models.DAL.<REMOVED>.ssdl|res://*/Models.DAL.<REMOVED>.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=<REMOVED>;initial catalog=<REMOVED>;persist security info=True;user id=<REMOVED>;password=<REMOVED>;MultipleActiveResultSets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />

<!--unity setting-->
<unity>
    <containers>
        <types>
            <register type="API.Areas.HelpPage.Controllers.HelpController, API">
                <constructor>
                    <param valu=""></param>
            </constructor>
            </register>
        </types>
    </containers>
</unity>

我是朝着正确的方向前进吗？

由于

更新： helpcontroller.cs：

public class HelpController : Controller
    {
        public HelpController()
            : this(GlobalConfiguration.Configuration)
        {
        }

        public HelpController(HttpConfiguration config)
        {
            Configuration = config;
        }

        public HttpConfiguration Configuration { get; private set; }

        public ActionResult Index()
        {
            return View(Configuration.Services.GetApiExplorer().ApiDescriptions);
        }

        public ActionResult Api(string apiId)
        {
            if (!String.IsNullOrEmpty(apiId))
            {
                HelpPageApiModel apiModel = Configuration.GetHelpPageApiModel(apiId);
                if (apiModel != null)
                {
                    return View(apiModel);
                }
            }

            return View("Error");
        }
    }

url我正在尝试访问：http：// hostname：port / Help

Answer 1

我认为更好的方法是将InjectionConstructor属性添加到默认构造函数中。此属性强制unity使用装饰的构造函数。

示例：

public class HelpController : Controller
{
    private const string ErrorViewName = "Error";

    [InjectionConstructor]
    public HelpController()
        : this(GlobalConfiguration.Configuration)
    {
    }

Answer 2

作为您的代码示例，我假设您使用的是Controller而不是API控制器（来自web api）。

您的api控制器依赖HttpConfiguration的构造函数。容器概率上没有此类型的定义，因此不知道如何解决它，并且错误消息上的string应该来自此类型作为依赖项。我建议您使用GlobalConfiguration静态类并访问Configuration属性以获取HttpConfiguration实例。您可以在属性中抽象它，例如：

// include this namespace
using System.Web.Http;

public class HelpController : Controller
{
    // remove the constructors...

    // property
    protected static HttpConfiguration Configuration
    {
        get { return GlobalConfiguration.Configuration; }
    }

    public ActionResult Index()
    {
        return View(this.Configuration.Services.GetApiExplorer().ApiDescriptions);
    }

    public ActionResult Api(string apiId)
    {
        if (!String.IsNullOrEmpty(apiId))
        {
            HelpPageApiModel apiModel = this.Configuration.GetHelpPageApiModel(apiId);
            if (apiModel != null)
            {
                return View(apiModel);
            }
        }

        return View("Error");
    }
}

现在，如果您使用的是Api Controller，您只需直接访问ApiController上已有的this.Configuration属性（Api控制器的基类），并获取HttpConfiguration的实例。< / p>

Answer 3

发生这种情况的原因是因为Unity默认选择使用具有最多参数的构造函数，从而绕过默认构造函数。

注释掉HelpController模板中存在的两个构造函数，并添加一个设置配置的默认构造函数。

    //public HelpController()
    //    : this(GlobalConfiguration.Configuration)
    //{
    //}

    //public HelpController(HttpConfiguration config)
    //{
    //    Configuration = config;
    //}

    public HelpController()
    {
        Configuration = GlobalConfiguration.Configuration;
    }

Answer 4

将HttpConfiguration对象注册为UnityContainer中的实例也有助于解决问题只需在UnityContainer注册时添加以添加以下行。

public static void RegisterTypes(IUnityContainer container) {
    container.RegisterInstance<HttpConfiguration>(GlobalConfiguration.Configuration);
}

这将有助于Unity在使用参数调用构造函数时解析config参数。

public HelpController(HttpConfiguration config) {
    Configuration = config;
}

Answer 5

我最近在以前正在运行的代码库上发生了此错误。以下答案显示了我为纠正它所做的工作：

Adding Web API and API documentation to an existing MVC project

基本上使用参数protected而不是public

构建构造函数

无法构造String类型

5 个答案: