asp.net-web-api – 不能构造String类型

发布时间：2020-12-16 00:38:34 所属栏目：asp.Net 来源：网络整理

导读：我正在使用Web.api和Unity，当我尝试打开默认的“帮助”区域时，我收到以下错误： [InvalidOperationException: The type String cannot be constructed. You must configure the container to supply this value.]Microsoft.Practices.ObjectBuilder2.Dynam

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

[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,IEnumerable`1 resolverOverrides) +436
   Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t,IEnumerable`1  resolverOverrides) +50
   Microsoft.Practices.Unity.UnityContainer.Resolve(Type t,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,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

我是新来的团结，我确定我错过了一步。
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)
    {

    }
  }

我尝试在一个web.config
web.config中

<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>

我朝着正确的方向前进吗？

谢谢

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

解决方法

作为你的代码示例，我假设你是一个控制器，而不是一个API控制器(从web api)。

您的api控制器依赖于HttpConfiguration的构造函数。容器可能没有这种类型的定义，因此不知道如何解决它，并且错误消息上的字符串应该来自这种类型作为依赖。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出样本：

// 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控制器，则只需直接访问ApiController(Api控制器的基类)上的this.Configuration属性，并获取一个HttpConfiguration实例。

（编辑：李大同）

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