确保控制器在web api中有一个无参数的公共构造函数？

Question

我正在努力解决使用统一的依赖注入问题。我根据这个链接实施了qazxsw poi

但得到了这个错误：

https://www.asp.net/web-api/overview/advanced/dependency-injection

我的Web Api控制器：

{
  "Message": "An error has occurred.",
  "ExceptionMessage": "An error occurred when trying to create a controller of type 'WebAPIController'. 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 'Fairmoves.Controllers.WebAPIController' does not have a default constructor",
    "ExceptionType": "System.ArgumentException",
    "StackTrace": "   at System.Linq.Expressions.Expression.New(Type type)\r\n   at System.Web.Http.Internal.TypeActivator.Create[TBase](Type instanceType)\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)"
  }
}

UnityResolver.cs：

[RoutePrefix("api/WebAPI")]
public class WebAPIController : ApiController
{
    private readonly IUserBusinessService UserBusinessService;
    private readonly ILoginBusinessService LoginBusinessService;

    //public WebAPIController():base()
    //{
    //}

    public WebAPIController(IUserBusinessService UserBusinessService, ILoginBusinessService LoginBusinessService)
    {
        this.UserBusinessService = UserBusinessService;
        this.LoginBusinessService = LoginBusinessService;
    }
    [HttpPost]
    public IHttpActionResult Login([FromBody]AuthModels.LoginModel model)
    {
        // string strUserId = credentials.LoginName;
        //string strPassword = credentials.Password;
        var serviceResultDAO1 =  LoginBusinessService.LoginUserSubmit(model.LoginName);
    }
}

}

WebApiConfig.cs：

public class UnityResolver:IDependencyResolver
{
    protected IUnityContainer container;

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

    [DebuggerStepThrough]
    public object GetService(Type serviceType)
    {
        try
        {
            return container.Resolve(serviceType);
        }
        catch (ResolutionFailedException)
        {
            return null;
        }
    }

    [DebuggerStepThrough]
    public IEnumerable<object> GetServices(Type serviceType)
    {
        try
        {
            return container.ResolveAll(serviceType);
        }
        catch (ResolutionFailedException)
        {
            return new List<object>();
        }
    }

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

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

}

无法确定问题所在？请进入代码并告诉我。我已经按照以下所有这些链接

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        //config.DependencyResolver = new NinjectResolver();

        var container = new UnityContainer();
        container.RegisterType<ILoginBusinessService, LoginBusinessService>(new HierarchicalLifetimeManager());
        container.RegisterType<IUserBusinessService, UserBusinessService>(new HierarchicalLifetimeManager());
        config.DependencyResolver = new UnityResolver(container);
        //DependencyResolver.SetResolver(new UnityDependencyResolver(container));

        config.MapHttpAttributeRoutes();

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

Make sure that the controller has a parameterless public constructor?

Autofac - Make sure that the controller has a parameterless public constructor

Make sure that the controller has a parameterless public constructor using Ninject

但这些都没有解决我的问题。

Answer 1

由于我在一个项目中同时使用MVC和WebAPI，我通过使用这个Make sure that the controller has a parameterless public constructor error来理解我需要解决两个依赖项。

所以，我在WebAPIConfig.cs文件中删除了以下代码

link

我在我的项目中安装了一个名为Unity.WebAPI的软件包。

在UnityConfig.cs文件中添加了以下代码

var container = new UnityContainer();
    container.RegisterType<ILoginBusinessService, LoginBusinessService>(new HierarchicalLifetimeManager());
    container.RegisterType<IUserBusinessService, UserBusinessService>(new HierarchicalLifetimeManager());
    config.DependencyResolver = new UnityResolver(container);

就是这样，解决了我的问题！

Answer 2

我猜你正在将WebAPI合并到MVC中，它紧密耦合，现在通过添加一个GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container); 进行解耦，因此我和上面提到的@Edukondalu thaviti一样，除了改变那些对我有用的小代码。

1. 使用Dependency injection安装Unity.WebAPI和Unity.WebApi.5.1 注意：安装完成后对话框将打开并要求您覆盖Manage Nuget Packages文件，只需选择Unity.Config.cs
2. 确保在No文件中的UnityConfig.RegisterComponents();方法中存在Application_Start()
3. 现在包括 在Global.asax.cs文件中的

   container.RegisterType<IWebAPIBusinessService, WebAPIBusinessService>();
   container.RegisterType<IWebAPIDomainService, WebAPIDomainService>();
   container.RegisterType<IWebAPIDataService, WebAPIDataService>();
   GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container);

   方法中的RegisterComponents()。假设您已经为当前类创建了实例。

现在运行你的项目。上面的代码对我很有帮助，如果你克服任何错误，请纠正我。