【WebAPI】Custom ActionFilter Order

ActionAttribute

環境 : WebAPI 2.2 詳細

在WebAPI中，通常都繪有需要客製化ActionFilter的情況發生

執行順序不固定

ActionFilter的執行順序並非在上面的就優先執行，Filter有個FilterScope來表示他屬於何種層級的ActionFilter，執行順序依次是 Global , Controller , Action 。但如果是在同一層級的ActionFilter順序則未必按照固定。

]

測試

裡面全部都一樣繼承ActionFilterAttribute即可

public class FourAttribute :ActionFilterAttribute{ }

註冊OneAttribute到Global

將其它Attribute分別註冊到Controller與Action

在Get中補上以下程式然後執行看看

[HttpGet]
[Three]
[Four]
public IEnumerable<Tuple<string,string>> Get()
{
    IHttpActionSelector actionSelector =
        this.Configuration.Services.GetActionSelector();
 
    HttpActionDescriptor actionDescriptor =
        actionSelector.SelectAction(this.ControllerContext);
 
    foreach (FilterInfo filterInfo in actionDescriptor.GetFilterPipeline())
    {
        yield return new Tuple<string, string>(
            filterInfo.Instance.GetType().Name,
            filterInfo.Scope.ToString()
        );
    }
}

測試結果

排序依據所對應的層級，雖然這邊排序與我們在程式上的排序相同。但實際上順序同層級的順序未必是由上而下，為了避免這樣的問題，最好的方法就是在ActionFilter加上排序的屬性來解決。

實作Order屬性

定義IOrderAttribute

public interface IOrderAttribute
{
   int Order { get; set; }
}

public class FourAttribute : ActionFilterAttribute, IOrderAttribute
{
   public int Order { get; set; }
}

實做IComparable介面

public class CustomFilterInfo : IComparable
    {
        public IFilter Instance { get; set; }
        public FilterScope Scope { get; set; }
 
        //FilterInfo
        public CustomFilterInfo(IFilter instance, FilterScope scope)
        {
            this.Instance = instance;
            this.Scope = scope;
        }
 
        public int CompareTo(object obj)
        {
            if (obj is CustomFilterInfo)
            {
                var item = obj as CustomFilterInfo;
 
                if (item.Instance is IAttribute)
                {
                    var attr = item.Instance as IAttribute;
                    return (this.Instance as IAttribute).Order.CompareTo(attr.Order);
                }
            }
 
            return 0;
        }
 
        public FilterInfo ConvertToFilterInfo()
        {
            return new FilterInfo(this.Instance, this.Scope);
        }
    }

實做IFilterProvider介面

public class CustomFilterProvider : IFilterProvider
{
    public IEnumerable<FilterInfo> GetFilters(
        HttpConfiguration configuration, 
        HttpActionDescriptor actionDescriptor)
    {
        IEnumerable<CustomFilterInfo> customActionFilters =
            actionDescriptor.GetFilters()
                            .Select(i => new CustomFilterInfo(i, FilterScope.Controller));
 
        IEnumerable<CustomFilterInfo> customControllerFilters =
            actionDescriptor.ControllerDescriptor
                            .GetFilters()
                            .Select(i => new CustomFilterInfo(i, FilterScope.Controller));
 
        return customControllerFilters.Concat(customActionFilters)
                                      .OrderBy(i => i)
                                      .Select(i => i.ConvertToFilterInfo());
 
    }
}

Global註冊

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    GlobalConfiguration.Configure(WebApiConfig.Register);
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();
 
    //註冊Global Attribute
    GlobalConfiguration.Configuration.Filters.Add(new OneAttribute());
 
     
    //新增CustomFilterProvider
    GlobalConfiguration.Configuration.Services.Add(
        typeof(System.Web.Http.Filters.IFilterProvider), new CustomFilterProvider());
 
    var providers = GlobalConfiguration.Configuration.Services.GetFilterProviders();
    var defaultprovider = providers.First(i => i is ActionDescriptorFilterProvider);
 
    //移除DefaultProvider
    GlobalConfiguration.Configuration.Services.Remove(
        typeof(System.Web.Http.Filters.IFilterProvider),
        defaultprovider);
}

測試

將Attibute補上Order再執行看看得到的順序

可以看到Four排在Three的前面了