ASP.NET MVC ActionMethodSelectorAttribute 以及HttpGet等Action特性

一、ActionMethodSelectorAttribute

　　其是一个抽象类，继承自Attribute，子类有NonActionAttribute、HttpGetAttribute、HttpPostAttribute、HttpPutAttribute、HttpDeleteAttribute、HttpPatchAttribute、HttpHeadAttribute、HttpOptionsAttribute和AcceptVerbsAttribute,其唯一抽象方法IsValidForRequest，如果返回false，结果会提示Action Not Found

[AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
public abstract class ActionMethodSelectorAttribute : Attribute
{
    public abstract bool IsValidForRequest(ControllerContext controllerContext, MethodInfo methodInfo);
}　　

AcceptVerbsAttribute 直接继承 ActionMethodSelectorAttribute

[AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
    public sealed class AcceptVerbsAttribute : ActionMethodSelectorAttribute
    {
        public AcceptVerbsAttribute(HttpVerbs verbs)
            : this(EnumToArray(verbs))
        {
        }

        public AcceptVerbsAttribute(params string[] verbs)
        {
            if (verbs == null || verbs.Length == 0)
            {
                throw new ArgumentException(MvcResources.Common_NullOrEmpty, "verbs");
            }

            Verbs = new ReadOnlyCollection<string>(verbs);
        }

        public ICollection<string> Verbs { get; private set; }

        private static void AddEntryToList(HttpVerbs verbs, HttpVerbs match, List<string> verbList, string entryText)
        {
            if ((verbs & match) != 0)
            {
                verbList.Add(entryText);
            }
        }

        internal static string[] EnumToArray(HttpVerbs verbs)
        {
            List<string> verbList = new List<string>();

            AddEntryToList(verbs, HttpVerbs.Get, verbList, "GET");
            AddEntryToList(verbs, HttpVerbs.Post, verbList, "POST");
            AddEntryToList(verbs, HttpVerbs.Put, verbList, "PUT");
            AddEntryToList(verbs, HttpVerbs.Delete, verbList, "DELETE");
            AddEntryToList(verbs, HttpVerbs.Head, verbList, "HEAD");
            AddEntryToList(verbs, HttpVerbs.Patch, verbList, "PATCH");
            AddEntryToList(verbs, HttpVerbs.Options, verbList, "OPTIONS");

            return verbList.ToArray();
        }

        public override bool IsValidForRequest(ControllerContext controllerContext, MethodInfo methodInfo)
        {
            if (controllerContext == null)
            {
                throw new ArgumentNullException("controllerContext");
            }

            string incomingVerb = controllerContext.HttpContext.Request.GetHttpMethodOverride();

            return Verbs.Contains(incomingVerb, StringComparer.OrdinalIgnoreCase);
        }
    }

　　除了NonActionAttribute，内部都是通过AcceptVerbsAttribute 来实现的，如HttpGetAttribute,其他都类似

  [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
    public sealed class HttpGetAttribute : ActionMethodSelectorAttribute
    {
        private static readonly AcceptVerbsAttribute _innerAttribute = new AcceptVerbsAttribute(HttpVerbs.Get);

        public override bool IsValidForRequest(ControllerContext controllerContext, MethodInfo methodInfo)
        {
            return _innerAttribute.IsValidForRequest(controllerContext, methodInfo);
        }
    }

　　NonActionAttribute，IsValidForRequest直接返回false

 [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
    public sealed class NonActionAttribute : ActionMethodSelectorAttribute
    {
        public override bool IsValidForRequest(ControllerContext controllerContext, MethodInfo methodInfo)
        {
            return false;
        }
    }

二、ActionNameSelectorAttribute

　　其是一个抽象类，继承自Attribute，子类有ActionNameAttribute

 [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
    public abstract class ActionNameSelectorAttribute : Attribute
    {
        public abstract bool IsValidName(ControllerContext controllerContext, string actionName, MethodInfo methodInfo);
    }

    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
    public sealed class ActionNameAttribute : ActionNameSelectorAttribute
    {
        public ActionNameAttribute(string name)
        {
            if (String.IsNullOrEmpty(name))
            {
                throw new ArgumentException(MvcResources.Common_NullOrEmpty, "name");
            }

            Name = name;
        }

        public string Name { get; private set; }

        public override bool IsValidName(ControllerContext controllerContext, string actionName, MethodInfo methodInfo)
        {
　　　　　　　//只是验证根据请求进行路由匹配出的actionName，是否和ActionName特性上指定的Name相等
            return String.Equals(actionName, Name, StringComparison.OrdinalIgnoreCase);
        }
    }

三、自定义ActionMethodSelectorAttribute

　　验证请求是GET而且是ajax的

 public class MyActionMethodSelectorAttribute : ActionMethodSelectorAttribute
        {
            public override bool IsValidForRequest(ControllerContext controllerContext, System.Reflection.MethodInfo methodInfo)
            {
                //get/post
                string httpMethodOverride = controllerContext.HttpContext.Request.GetHttpMethodOverride();

                //isAjax
                var isAjax = controllerContext.HttpContext.Request.IsAjaxRequest();

                var b = httpMethodOverride.ToLower() == "get" && isAjax;

                return b;
            }
        }