c# - 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有一个奇怪的行为。在一个简单的测试 webapi 应用程序中，我有以下 DryIoc 注册类，它在 WebApi 配置注册后立即被调用。

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 Controller :

public class ValuesController : ApiController
{
    private readonly IWidgetService _widgetService;

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

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

这似乎工作正常，但在我看来似乎是相同的，但写得有点冗长，代码我得到一个错误。

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);
    }
}

我得到的异常如下(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)"
        }
    }

这对 DryIoc 来说是不是有些奇怪，或者这是我从未遇到过的 C# 细微差别？

Answer 1

这是因为 .WithWebApi() 是根据 source 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，并将该新创建的实例传递给 .WithWebApi()。这反过来会更新容器实例，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 BACK 的值返回到原始变量，更新它。您调用它就好像它是一个 void 方法，在这种情况下它什么都不做，因此是异常。

如果你改为写:

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

它本质上是第一种语法的更详细的示例，并且会使用新功能正确更新 c。