实现MVC自定义过滤器，自定义Area过滤器，自定义Controller，Action甚至是ViewData过滤器

MVC开发中几种以AOP方式实现的Filters是非常好用的，默认情况下，我们通过App_Start中的FilterConfig来实现的过滤器注册是全局的，也就是整个应用程序都会使用的，针对单独的Filter我们不得不去单独的Controller或者Action去定义

如图：

那么问题来了，我现在想在FitlerConfig里面去维护所有的过滤器，但是又想实现自定义的过滤器该咋搞，MVC默认不支持！

我们先来看看，MVC默认的Fitlers注册是怎样的
官方源码：GlobalFilterCollection.cs

 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web.Mvc.Filters;
 using System.Web.Mvc.Properties;

 namespace System.Web.Mvc
 {
     public sealed class GlobalFilterCollection : IEnumerable<Filter>, IFilterProvider
     {
         private List<Filter> _filters = new List<Filter>();

         public int Count
         {
             get { return _filters.Count; }
         }

         public void Add(object filter)
         {
             AddInternal(filter, order: null);
         }

         public void Add(object filter, int order)
         {
             AddInternal(filter, order);
         }

         private void AddInternal(object filter, int? order)
         {
             ValidateFilterInstance(filter);
             _filters.Add(new Filter(filter, FilterScope.Global, order));
         }

         public void Clear()
         {
             _filters.Clear();
         }

         public bool Contains(object filter)
         {
             return _filters.Any(f => f.Instance == filter);
         }

         public IEnumerator<Filter> GetEnumerator()
         {
             return _filters.GetEnumerator();
         }

         IEnumerator IEnumerable.GetEnumerator()
         {
             return _filters.GetEnumerator();
         }

         IEnumerable<Filter> IFilterProvider.GetFilters(ControllerContext controllerContext,
             ActionDescriptor actionDescriptor)
         {
             return this;
         }

         public void Remove(object filter)
         {
             _filters.RemoveAll(f => f.Instance == filter);
         }

         private static void ValidateFilterInstance(object instance)
         {
             if (instance != null && !(
                 instance is IActionFilter ||
                 instance is IAuthorizationFilter ||
                 instance is IExceptionFilter ||
                 instance is IResultFilter ||
                 instance is IAuthenticationFilter))
             {
                 throw Error.InvalidOperation(MvcResources.GlobalFilterCollection_UnsupportedFilterInstance,
                     typeof(IAuthorizationFilter).FullName,
                     typeof(IActionFilter).FullName,
                     typeof(IResultFilter).FullName,
                     typeof(IExceptionFilter).FullName,
                     typeof(IAuthenticationFilter).FullName);
             }
         }
     }
 }

GlobalFilters.cs

 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

 namespace System.Web.Mvc
 {
     public static class GlobalFilters
     {
         static GlobalFilters()
         {
             Filters = new GlobalFilterCollection();
         }

         public static GlobalFilterCollection Filters { get; private set; }
     }
 }

再看看，App_Start里面的FilterConfig.cs

 public class FilterConfig
     {
         public static void RegisterGlobalFilters(GlobalFilterCollection filters)
         {
             filters.Add(new HandleErrorAttribute());
         }
     }

可以发现，其实是GlobalFilters里面定义了静态的GlobalFIlterCollection对象，然后通过FilterConfig像这个静态的集合注册Filters，那么我们没看到MVC哪调用了这个集合，是的，Global里面是没有明确写出来，但是我们来看看FilterProviders.cs的源码

 namespace System.Web.Mvc
 {
     public static class FilterProviders
     {
         static FilterProviders()
         {
             Providers = new FilterProviderCollection();
             Providers.Add(GlobalFilters.Filters);
             Providers.Add(new FilterAttributeFilterProvider());
             Providers.Add(new ControllerInstanceFilterProvider());
         }

         public static FilterProviderCollection Providers { get; private set; }
     }
 }

在静态的构造函数中就已经通过Providers.Add(GlobalFilters.Filters);把GlobalFilters.Filters集合给添加进去了，然后MVC每次请求会调用IFilterProvider.GetFilters，那为什么自带的GlobalFilterCollection就不能实现自定义的过滤器呢，请看最上面GlobalFilterCollection.cs的GetFilters代码，他直接返回所有的Filters，而且这个类不能重写，好吧！我们来自己写一个实现自定义过滤器！
可以完全照搬GlobalFilterCollection.cs，GlobalFilters.cs代码，然后根据自己的需求改改
这里我们要通过GetFilters实现自己的筛选规则
看看原始方法源码：

IEnumerable<Filter> IFilterProvider.GetFilters(ControllerContext controllerContext,
            ActionDescriptor actionDescriptor)
        {
            return this;
        }

这个方法传进来两个参数：ControllerContext和ActionDescriptor
我们添加Add方法

/// <summary>
        /// 注册注册局部规则过滤器
        /// </summary>
        /// <param name="func"></param>
        /// <param name="filter"></param>
        /// <param name="order"></param>
        public void Add(Func<ControllerContext, ActionDescriptor, bool> func, object filter, int order)
        {
            Add(func, filter, order);
        }

        private void Add(Func<ControllerContext, ActionDescriptor, bool> func, object filter, int? order)
        {
            ValidateFilterInstance(filter);
            items.Add(new FilterItem
            {
                filter = new Filter(filter, FilterScope.Global, order),
                func = func
            });
        }

FilterItem是我自己写的一个类，用来存储设置的Filters跟规则的Func

public class FilterItem
    {
        public Filter filter { get; set; }
        public Func<ControllerContext, ActionDescriptor, bool> func { get; set; }
    }

然后改造GetFilters方法

public IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
        {
            foreach (FilterItem item in items)
            {
                if (item.func == null)
                {
                    yield return item.filter;
                }
                else
                {
                    bool result = item.func(controllerContext, actionDescriptor);
                    if (result)
                        yield return item.filter;
                }
            }
        }

这样在执行GetFilters的时候就会根据注册的所有Filters进行筛选匹配出符合条件的Filters
最后App_Start中自定义FilterConfig注册Filtes
然后在Global添加自定义的Filters注册
FilterProviders.Providers.Add(Geo.Mvc.Provider.GlobalFilters.Filters);

测试：

新建HomeController，写上两个Action分别为Index和Test

public ActionResult Index()
        {
            return Content("Index");
        }

        public ActionResult Test()
        {
            return Content("test");
        }

自己随便写个Filter测试

public class TestFilter : IActionFilter
    {

        public void OnActionExecuted(ActionExecutedContext filterContext)
        {
            filterContext.HttpContext.Response.Write("执行前！<br/>");
        }

        public void OnActionExecuting(ActionExecutingContext filterContext)
        {
            filterContext.HttpContext.Response.Write("执行后！<br/>");
        }
    }

去App_Start中自定义的Filter注册

public class MyFilterConfig
    {
        public static void RegistGlobalFilters(Geo.Mvc.Provider.MyFlterCollection filters)
        {
            //filters.Add(new Filters.TestFilter());
            filters.Add((c, a) =>
            {
                return string.Compare(a.ActionName, "test", true) == 0;
            }, new Filters.TestFilter());
        }
    }

最后执行Index跟Test方法
结果如下：

这个就是当初我们所希望实现的效果！

不知道怎么放附件，我直接贴我的代码好了！

 public static class GlobalFilters
     {
         static GlobalFilters()
         {
             Filters = new MyFlterCollection();
         }

         public static MyFlterCollection Filters { get; private set; }
     }

     public class MyFlterCollection : IEnumerable<Filter>, IFilterProvider
     {
         List<FilterItem> items = new List<FilterItem>();
         /// <summary>
         /// Filter数量
         /// </summary>
         public int Count
         {
             get
             {
                 return items.Count;
             }
         }
         /// <summary>
         /// 注册全局过滤器
         /// </summary>
         /// <param name="filter"></param>
         public void Add(object filter)
         {
             Add(null, filter, null);
         }
         /// <summary>
         /// 注册全局过滤器
         /// </summary>
         /// <param name="filter"></param>
         /// <param name="order"></param>
         public void Add(object filter, int order)
         {
             Add(null, filter, order);
         }
         /// <summary>
         /// 注册注册局部规则过滤器
         /// </summary>
         /// <param name="func"></param>
         /// <param name="filter"></param>
         public void Add(Func<ControllerContext, ActionDescriptor, bool> func, object filter)
         {
             Add(func, filter, null);
         }
         /// <summary>
         /// 注册注册局部规则过滤器
         /// </summary>
         /// <param name="func"></param>
         /// <param name="filter"></param>
         /// <param name="order"></param>
         public void Add(Func<ControllerContext, ActionDescriptor, bool> func, object filter, int order)
         {
             Add(func, filter, order);
         }

         private void Add(Func<ControllerContext, ActionDescriptor, bool> func, object filter, int? order)
         {
             if(ValidateFilterInstance(filter))
             items.Add(new FilterItem
             {
                 filter = new Filter(filter, FilterScope.Global, order),
                 func = func
             });
         }
         /// <summary>
         /// 获取过滤器
         /// </summary>
         /// <param name="controllerContext"></param>
         /// <param name="actionDescriptor"></param>
         /// <returns></returns>
         public IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
         {
             foreach (FilterItem item in items)
             {
                 if (item.func == null)
                 {
                     yield return item.filter;
                 }
                 else
                 {
                     bool result = item.func(controllerContext, actionDescriptor);
                     if (result)
                         yield return item.filter;
                 }
             }
         }

         public IEnumerator<Filter> GetEnumerator()
         {
             return this.GetEnumerator();
         }

         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
         {
             return this.GetEnumerator();
         }

         /// <summary>
         /// 清除所有过滤器
         /// </summary>
         public void Clear()
         {
             items.Clear();
         }
         /// <summary>
         /// 是否包含过滤器
         /// </summary>
         /// <param name="filter"></param>
         /// <returns></returns>
         public bool Contains(object filter)
         {
             return items.Any(t => t.filter.Instance == filter);
         }
         /// <summary>
         /// 删除过滤器
         /// </summary>
         /// <param name="filter"></param>
         public void Remove(object filter)
         {
             items.RemoveAll(t => t.filter.Instance == filter);
         }

         /// <summary>
         /// 验证过滤器是否为IActionFilter，IAuthorizationFilter，IExceptionFilter，IResultFilter
         /// </summary>
         /// <param name="instance"></param>
         /// <returns></returns>
         private static bool ValidateFilterInstance(object instance)
         {
             if (instance == null) return false;
             return
                 instance is IActionFilter ||
                 instance is IAuthorizationFilter ||
                 instance is IExceptionFilter ||
                 instance is IResultFilter;
         }
     }
     /// <summary>
     /// 存储
     /// </summary>
     public class FilterItem
     {
         public Filter filter { get; set; }
         public Func<ControllerContext, ActionDescriptor, bool> func { get; set; }
     }

Global.asax的Application_start中

 //FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
             MyFilterConfig.RegistGlobalFilters(Geo.Mvc.Provider.GlobalFilters.Filters);
             FilterProviders.Providers.Add(Geo.Mvc.Provider.GlobalFilters.Filters);

最后App_Start中的MyFilterConfig.cs

 public class MyFilterConfig
     {
         public static void RegistGlobalFilters(Geo.Mvc.Provider.MyFlterCollection filters)
         {
             //filters.Add(new Filters.TestFilter());
             filters.Add((c, a) =>
             {
                 return string.Compare(a.ActionName, "test", true) == ;
             }, new Filters.TestFilter());
         }
     }

OK!