public abstract class ControllerDescriptor : ICustomAttributeProvider, IUniquelyIdentifiable
    {
       
        public abstract ActionDescriptor FindAction(ControllerContext controllerContext, string actionName);
       
        public virtual object[] GetCustomAttributes(bool inherit);
      
        public virtual object[] GetCustomAttributes(Type attributeType, bool inherit);
       
        public virtual IEnumerable<FilterAttribute> GetFilterAttributes(bool useCache);
       
        
        public virtual bool IsDefined(Type attributeType, bool inherit);
    }

 1 public override ActionDescriptor FindAction(ControllerContext controllerContext, string actionName)
 2         {
 3             //省略非相关代码
 4     
 5             MethodInfo matched = _selector.FindActionMethod(controllerContext, actionName);
 6             if (matched == null)
 7             {
 8                 return null;
 9             }
10 
11             return new ReflectedActionDescriptor(matched, actionName, this);
12         }    

 1  public MethodInfo FindActionMethod(ControllerContext controllerContext, string actionName)
 2         {
 3             //省略非相关代码
 4     
 5             List<MethodInfo> finalMethods = FindActionMethods(controllerContext, actionName);
 6 
 7             switch (finalMethods.Count)
 8             {
 9                 case 0:
10                     return null;
11 
12                 case 1:
13                     return finalMethods[0];
14 
15                 default:
16                     throw CreateAmbiguousActionMatchException(finalMethods, actionName);
17             }
18         }

 1  protected List<MethodInfo> FindActionMethods(ControllerContext controllerContext, string actionName)
 2         {
 3             List<MethodInfo> matches = new List<MethodInfo>();
 4 
 5             // Performance sensitive, so avoid foreach
 6             for (int i = 0; i < AliasedMethods.Length; i++)
 7             {
 8                 MethodInfo method = AliasedMethods[i];
 9                 if (IsMatchingAliasedMethod(method, controllerContext, actionName))
10                 {
11                     matches.Add(method);
12                 }
13             }
14             matches.AddRange(NonAliasedMethods[actionName]);
15             RunSelectionFilters(controllerContext, matches);
16             return matches;
17         }

 1  protected static void RunSelectionFilters(ControllerContext controllerContext, List<MethodInfo> methodInfos)
 2         {
 3             // Filter depending on the selection attribute.
 4             // Methods with valid selection attributes override all others.
 5             // Methods with one or more invalid selection attributes are removed.
 6 
 7             bool hasValidSelectionAttributes = false;
 8             // loop backwards for fastest removal
 9             for (int i = methodInfos.Count - 1; i >= 0; i--)
10             {
11                 MethodInfo methodInfo = methodInfos[i];
12                 ReadOnlyCollection<ActionMethodSelectorAttribute> attrs = ReflectedAttributeCache.GetActionMethodSelectorAttributesCollection(methodInfo);
13                 if (attrs.Count == 0)
14                 {
15                     // case 1: this method does not have a MethodSelectionAttribute
16 
17                     if (hasValidSelectionAttributes)
18                     {
19                         // if there is already method with a valid selection attribute, remove method without one
20                         methodInfos.RemoveAt(i);
21                     }
22                 }
23                 else if (IsValidMethodSelector(attrs, controllerContext, methodInfo))
24                 {
25                     // case 2: this method has MethodSelectionAttributes that are all valid
26 
27                     // if a matching action method had a selection attribute, consider it more specific than a matching action method
28                     // without a selection attribute
29                     if (!hasValidSelectionAttributes)
30                     {
31                         // when the first selection attribute is discovered, remove any items later in the list without selection attributes
32                         if (i + 1 < methodInfos.Count)
33                         {
34                             methodInfos.RemoveFrom(i + 1);
35                         }
36                         hasValidSelectionAttributes = true;
37                     }
38                 }
39                 else
40                 {
41                     // case 3: this method has a method selection attribute but it is not valid
42 
43                     // remove the method since it is opting out of this request
44                     methodInfos.RemoveAt(i);
45                 }
46             }
47         }