asp.net-web-api - 构造函数依赖注入(inject) WebApi 属性

Question

我一直在寻找 WebApi 属性的非参数注入(inject)选项。

我的问题很简单，这是否真的可以使用 Structuremap？

我一直在谷歌搜索，但不断提出属性注入(inject)(我不喜欢使用)或构造函数注入(inject)的假设实现，到目前为止我无法复制。

我选择的容器是 Structuremap，但是任何示例都足够了，因为我能够转换它。

有人管理过这个吗？

Answer 1

是的，有可能。你(和大多数人一样)被微软的 Action 过滤器属性营销所吸引，这些属性被方便地放入一个类中，但对 DI 一点也不友好。

解决方案是将 Action 过滤器属性分成两部分as demonstrated in this post :

一个不包含任何行为来标记您的 Controller 和操作方法的属性。

一个实现 IActionFilter 的 DI 友好类并包含所需的行为。

方法是使用 IActionFilter 来测试属性是否存在，然后执行所需的行为。 Action 过滤器可以提供所有依赖项(通过构造函数)，然后在组合应用程序时注入(inject)。

IConfigProvider provider = new WebConfigProvider();
IActionFilter filter = new MaxLengthActionFilter(provider);
config.Filters.Add(filter);

NOTE: If you need any of the filter's dependencies to have a lifetime shorter than singleton, you will need to use a GlobalFilterProvider as in this answer.

要将其与 StructureMap 连接起来，您需要从 DI 配置模块返回一个容器实例。 Application_Start 方法仍然是组合根的一部分，因此您可以在此方法中的任何位置使用容器，它仍然不被视为服务定位器模式。请注意，我没有在此处显示完整的 WebApi 设置，因为我假设您已经使用 WebApi 进行了有效的 DI 配置。如果你需要一个，那是另一个问题。

public class DIConfig()
{
    public static IContainer Register()
    {
        // Create the DI container
        var container = new Container();

        // Setup configuration of DI
        container.Configure(r => r.AddRegistry<SomeRegistry>());
        // Add additional registries here...

        #if DEBUG
            container.AssertConfigurationIsValid();
        #endif

        // Return our DI container instance to the composition root
        return container;
    }
}

public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        // Hang on to the container instance so you can resolve
        // instances while still in the composition root
        IContainer container = DIConfig.Register();

        AreaRegistration.RegisterAllAreas();

        // Pass the container so we can resolve our IActionFilter
        WebApiConfig.Register(GlobalConfiguration.Configuration, container);
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
        BundleConfig.RegisterBundles(BundleTable.Bundles);
        AuthConfig.RegisterAuth();
    }
}

public static class WebApiConfig
{
    // Add a parameter for IContainer
    public static void Register(HttpConfiguration config, IContainer container)
    {
        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

        // Uncomment the following line of code to enable query support for actions with an IQueryable or IQueryable<T> return type.
        // To avoid processing unexpected or malicious queries, use the validation settings on QueryableAttribute to validate incoming queries.
        // For more information, visit http://go.microsoft.com/fwlink/?LinkId=279712.
        //config.EnableQuerySupport();

        // Add our action filter
        config.Filters.Add(container.GetInstance<IMaxLengthActionFilter>());
        // Add additional filters here that look for other attributes...
    }
}

MaxLengthActionFilter 的实现看起来像这样:

// Used to uniquely identify the filter in StructureMap
public interface IMaxLengthActionFilter : System.Web.Http.Filters.IActionFilter
{
}

public class MaxLengthActionFitler : IMaxLengthActionFilter
{
    public readonly IConfigProvider configProvider;

    public MaxLengthActionFilter(IConfigProvider configProvider)
    {
        if (configProvider == null)
            throw new ArgumentNullException("configProvider");
        this.configProvider = configProvider;
    }

    public Task<HttpResponseMessage> ExecuteActionFilterAsync(
        HttpActionContext actionContext,
        CancellationToken cancellationToken,
        Func<Task<HttpResponseMessage>> continuation)
    {
        var attribute = this.GetMaxLengthAttribute(filterContext.ActionDescriptor);
        if (attribute != null)
        {
            var maxLength = attribute.MaxLength;
            // Execute your behavior here (before the continuation), 
            // and use the configProvider as needed

            return continuation().ContinueWith(t =>
            {
                // Execute your behavior here (after the continuation), 
                // and use the configProvider as needed

                return t.Result;
            });
        }
        return continuation();
    }

    public bool AllowMultiple
    {
        get { return true; }
    }

    public MaxLengthAttribute GetMaxLengthAttribute(ActionDescriptor actionDescriptor)
    {
        MaxLengthAttribute result = null;

        // Check if the attribute exists on the action method
        result = (MaxLengthAttribute)actionDescriptor
            .GetCustomAttributes(typeof(MaxLengthAttribute), false)
            .SingleOrDefault();

        if (result != null)
        {
            return result;
        }

        // Check if the attribute exists on the controller
        result = (MaxLengthAttribute)actionDescriptor
            .ControllerDescriptor
            .GetCustomAttributes(typeof(MaxLengthAttribute), false)
            .SingleOrDefault();

        return result;
    }
}

而且，不应包含任何行为的属性应如下所示:

// This attribute should contain no behavior. No behavior, nothing needs to be injected.
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = false)]
public class MaxLengthAttribute : Attribute
{
    public MaxLengthAttribute(int maxLength)
    {
        this.MaxLength = maxLength;
    }

    public int MaxLength { get; private set; }
}