是的,这是可能的。你(和大多数人一样)正被微软的Action Filter Attributes营销所抛弃,这些属性很方便地放在一个类中,但对DI来说却一点都不友好。
解决方案是将Action Filter属性分成两部分
as demonstrated in this post
:
-
不包含用于标记控制器和操作方法的行为的属性。
-
实现的DI友好类
IActionFilter
并且包含期望的行为。
方法是使用IActionFilter测试属性的存在,然后执行所需的行为。可以(通过构造函数)向动作筛选器提供所有依赖项,然后在编写应用程序时注入。
IConfigProvider provider = new WebConfigProvider();
IActionFilter filter = new MaxLengthActionFilter(provider);
config.Filters.Add(filter);
注:
如果需要过滤器的任何依赖项的生存期比singleton短,则需要使用
GlobalFilterProvider
如中所示
this answer
.
要将其与StructureMap连接起来,需要从DI配置模块返回容器的实例。Application_Start方法仍然是组合根的一部分,因此您可以在该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。注意,我没有在这里显示完整的WebApi设置,因为我假设您已经使用WebApi进行了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的实现如下所示:
// 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,你的属性
不应包含任何行为
应该看起来像这样:
// 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; }
}
