DryIoc.WebApi设置

Question

我正在探索DryIoc在.NET WebAPI应用程序中的使用，并注意到初始化步骤中有一种奇怪的行为。在一个简单的测试webapi应用程序中，我有下面的DryIoc注册类，它在WebApi配置注册之后立即调用。

public class DryIocConfig
{
    public static void Register(HttpConfiguration config)
    {
        var c = new Container().WithWebApi(config);

        c.Register<IWidgetService, WidgetService>(Reuse.Singleton);
        c.Register<IWidgetRepository, WidgetRepository>(Reuse.Singleton);
    }
}

以及以下WebApi控制器：

public class ValuesController : ApiController
{
    private readonly IWidgetService _widgetService;

    public ValuesController(IWidgetService widgetService)
    {
        _widgetService = widgetService;
    }

    // GET api/values
    public IEnumerable<Widget> Get()
    {
        return _widgetService.GetWidgets();
    }
}

这似乎很好，但在我看来，在尝试是相同的，但写得更详细，代码我得到了一个错误。

public class DryIocConfig
{
    public static void Register(HttpConfiguration config)
    {
        var c = new Container();
        c.WithWebApi(config);  // Now separate statement rather than chained. 

        c.Register<IWidgetService, WidgetService>(Reuse.Singleton);
        c.Register<IWidgetRepository, WidgetRepository>(Reuse.Singleton);
    }
}

我得到的例外是以下(作为JSON)：

    {
        "Message" : "An error has occurred.",
        "ExceptionMessage" : "An error occurred when trying to create a controller of type 'ValuesController'. 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 'IOCContainerTest.DryLoc.Controllers.ValuesController' 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)"
        }
    }

这是DryIoc的奇怪之处，还是我从未遇到过的C#细微差别？

Answer 1

这是因为.WithWebApi()是每个来源的扩展方法。

 public static IContainer WithWebApi(this IContainer container, HttpConfiguration config,
        IEnumerable<Assembly> controllerAssemblies = null, IScopeContext scopeContext = null,
        Func<Type, bool> throwIfUnresolved = null)
    {
        container.ThrowIfNull();

        if (container.ScopeContext == null)
            container = container.With(scopeContext: scopeContext ?? new AsyncExecutionFlowScopeContext());

        container.RegisterWebApiControllers(config, controllerAssemblies);

        container.SetFilterProvider(config.Services);

        InsertRegisterRequestMessageHandler(config);

        config.DependencyResolver = new DryIocDependencyResolver(container, throwIfUnresolved);

        return container;
    }

在第一个语法示例中，您创建了一个新的Container实例，并将新创建的实例传递给.WithWebApi()。这反过来更新容器实例，并最终将其返回给变量c。

在第二个语法示例中，您永远不会将扩展方法的值返回到原始变量，并对其进行更新。您正在调用它，就好像它是一个void方法一样，在本例中它什么也不做，因此出现了异常。

如果你写的是：

var c = new Container();
c = c.WithWebApi(config);

它本质上是第一种语法的一个更详细的示例，并使用新的功能正确地更新了c。

Answer 2

这似乎很好，而且应该有效。显然，从ccontainer.WithWebApi(config);返回的容器不是原始容器，这在这一点上是出乎意料的，因此至少有一种代码气味，因为它会产生可能的bug。最好编写几个单元测试，并在DryIoC Bitbucket站点上打开一个问题。

为了帮助您，这里有一个如何编写此类测试的模板。创建一个新的测试项目并执行以下操作：

安装NuGet软件包

Install-Package Microsoft.AspNet.WebApi.OwinSelfHost
Install-Package DryIoc.WebApi.Owin.dll
Install-Package Xunit 

控制器

public sealed class ValuesController : ApiController
{
    private IWidgetService WidgetService { get; }

    public ValuesController(IWidgetService widgetService)
    {
        if(widgetService == null) 
            throw new ArgumentNullException(nameof(widgetService));
        WidgetService = widgetService;
    }

    [HttpGet]
    public IEnumerable<Widget> Get()
    {
        return WidgetService.GetWidgets().ToArray();
    }
}

OWIN启动

public sealed class Startup
{
    public void Configuration(IAppBuilder app)
    {
        var config = new HttpConfiguration()
            .ConfigureRouting()
            .ConfigureDependencyInjection();

        app.UseWebApi(config);

        // protip: use OWIN error page instead of ASP.NET yellow pages for better diagnostics 
        // Install-Package Microsoft.Owin.Diagnostics
        // app.UseErrorPage(ErrorPageOptions.ShowAll); 
    }

    private static HttpConfiguration ConfigureRouting(this HttpConfiguration config)
    {
        config.MapHttpAttributeRoutes();
        config.Routes.MapHttpRoute(
            name: "default", 
            routeTemplate: "/", 
            defaults: new { controller = "values" });
        return config;
    }

    private static HttpConfiguration ConfigureDependencyInjection(this HttpConfiguration config)
    {
        new Container()
            .Register<IWidgetService, WidgetService>(Reuse.Singleton)
            .Register<IWidgetRepository, WidgetRepository>(Reuse.Singleton)
            .WithWebApi(config);
        return config;
    }
}

单元测试

[Fact]
public async Task ShouldFoo()
{
    const string baseAddress = "http://localhost:8000";
    using (WebApp.Start<Startup>(baseAddress))
    {
        var httpclient = new HttpClient
        { 
            BaseAddress = new Uri(baseAddress)
        };
        var response = await httpclient.GetAsync("/");
        Assert.That(...);
    }
}