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服务器之家 - 编程语言 - ASP.NET教程 - asp.net mvc-Controllerl篇 ControllerDescriptor

asp.net mvc-Controllerl篇 ControllerDescriptor

2019-10-10 10:57asp.net技术网 ASP.NET教程

asp.net mvc-Controllerl篇 ControllerDescriptor

现在我们首先来看看ActionInvoker属性的定义吧: 

复制代码代码如下:


public IActionInvoker ActionInvoker { 
get { 
if (_actionInvoker == null) { 
_actionInvoker = CreateActionInvoker(); 

return _actionInvoker; 

set { 
_actionInvoker = value; 


protected virtual IActionInvoker CreateActionInvoker() { 
return new ControllerActionInvoker(); 


和TempDataProvider属性定义一样,大家一定要习惯这些代码啊。 
而ControllerActionInvoker的定义也很简单,但是这个类却不简单啊。 
让我们来看看你InvokeAction的定义吧: 

复制代码代码如下:


public virtual bool InvokeAction(ControllerContext controllerContext, string actionName) { 
if (controllerContext == null) { 
throw new ArgumentNullException("controllerContext"); 

if (String.IsNullOrEmpty(actionName)) { 
throw new ArgumentException(MvcResources.Common_NullOrEmpty, "actionName"); 


ControllerDescriptor controllerDescriptor = GetControllerDescriptor(controllerContext); 
ActionDescriptor actionDescriptor = FindAction(controllerContext, controllerDescriptor, actionName); 
if (actionDescriptor != null) { 
FilterInfo filterInfo = GetFilters(controllerContext, actionDescriptor); 

try { 
AuthorizationContext authContext = InvokeAuthorizationFilters(controllerContext, filterInfo.AuthorizationFilters, actionDescriptor); 
if (authContext.Result != null) { 
// the auth filter signaled that we should let it short-circuit the request 
InvokeActionResult(controllerContext, authContext.Result); 

else { 
if (controllerContext.Controller.ValidateRequest) { 
ValidateRequest(controllerContext); 


IDictionary<string, object> parameters = GetParameterValues(controllerContext, actionDescriptor); 
ActionExecutedContext postActionContext = InvokeActionMethodWithFilters(controllerContext, filterInfo.ActionFilters, actionDescriptor, parameters); 
InvokeActionResultWithFilters(controllerContext, filterInfo.ResultFilters, postActionContext.Result); 


catch (ThreadAbortException) { 
// This type of exception occurs as a result of Response.Redirect(), but we special-case so that 
// the filters don't see this as an error. 
throw; 

catch (Exception ex) { 
// something blew up, so execute the exception filters 
ExceptionContext exceptionContext = InvokeExceptionFilters(controllerContext, filterInfo.ExceptionFilters, ex); 
if (!exceptionContext.ExceptionHandled) { 
throw; 

InvokeActionResult(controllerContext, exceptionContext.Result); 


return true; 


// notify controller that no method matched 
return false; 


这个方法里面的内容不可能一次讲完的,我们看看 ControllerDescriptor controllerDescriptor = GetControllerDescriptor(controllerContext); 
很明显ControllerDescriptor是Controller实例的一个包装类。 

复制代码代码如下:


protected virtual ControllerDescriptor GetControllerDescriptor(ControllerContext controllerContext) { 
Type controllerType = controllerContext.Controller.GetType(); 
ControllerDescriptor controllerDescriptor = DescriptorCache.GetDescriptor(controllerType, () => new ReflectedControllerDescriptor(controllerType)); 
return controllerDescriptor; 


从这个方法中,我们可以知道实际返回的是一个ReflectedControllerDescriptor实例,它是ControllerDescriptor的子类,DescriptorCache.GetDescriptor(...)好像是从缓存中获取的啊,让我们证实一下吧,先来看看ControllerDescriptorCache的GetDescriptor方法: 

复制代码代码如下:


internal sealed class ControllerDescriptorCache : ReaderWriterCache<Type, ControllerDescriptor> { 
public ControllerDescriptor GetDescriptor(Type controllerType, Func<ControllerDescriptor> creator) { 
return FetchOrCreateItem(controllerType, creator); 


FetchOrCreateItem方法很简单,从缓存中获取ControllerDescriptor ,如果没有就创建并加入缓存然后在返回,缓存实现方式其实就是一个字典Dictionary<TKey, TValue>。 
现在看看ReflectedControllerDescriptor的够着函数是否有什么特别之处: 
_controllerType = controllerType; 
_selector = new ActionMethodSelector(_controllerType); 
怎么又有ActionMethodSelector这个东东啊,其构造函数如下 

复制代码代码如下:


public ActionMethodSelector(Type controllerType) { 
ControllerType = controllerType; 
PopulateLookupTables(); 

private void PopulateLookupTables() { 
MethodInfo[] allMethods = ControllerType.GetMethods(BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.Public); 
MethodInfo[] actionMethods = Array.FindAll(allMethods, IsValidActionMethod); 
AliasedMethods = Array.FindAll(actionMethods, IsMethodDecoratedWithAliasingAttribute); 
NonAliasedMethods = actionMethods.Except(AliasedMethods).ToLookup(method => method.Name, StringComparer.OrdinalIgnoreCase); 


这个方法很简单,找出ControllerType的所有实例、共有方法,然后在过滤调不是Action的,最后吧这些Action方法分成两部分,一部分有别名,一部分没有别名。 
现在我们已经得到了ControllerDescriptor实例,下面应该来看看ActionDescriptor actionDescriptor = FindAction(controllerContext, controllerDescriptor, actionName);这句代码了;同样我们可以确认ActionDescriptor实际上一个Action的包装类。 
protected virtual ActionDescriptor FindAction(ControllerContext controllerContext, ControllerDescriptor controllerDescriptor, string actionName)这个方法实际上就是调用 
ControllerDescriptor类FindAction方法,让我们看看你ReflectedControllerDescriptor的FindAction方法,该方法很简单,组要就2句代码: 

复制代码代码如下:


MethodInfo matched = _selector.FindActionMethod(controllerContext, actionName); 
return new ReflectedActionDescriptor(matched, actionName, this); 


_selector.FindActionMethod(controllerContext, actionName); 这句就是找到我们需要Action对应的MethodInfo。 

复制代码代码如下:


public MethodInfo FindActionMethod(ControllerContext controllerContext, string actionName) { 
List<MethodInfo> methodsMatchingName = GetMatchingAliasedMethods(controllerContext, actionName); 
methodsMatchingName.AddRange(NonAliasedMethods[actionName]); 
List<MethodInfo> finalMethods = RunSelectionFilters(controllerContext, methodsMatchingName); 

switch (finalMethods.Count) { 
case 0: 
return null; 

case 1: 
return finalMethods[0]; 

default: 
throw CreateAmbiguousMatchException(finalMethods, actionName); 


循环每个MethodInfo,查找它们的自定义的ActionMethodSelectorAttribute特性,如果有只返回验证通过的特性。看到ReflectedAttributeCache.GetActionMethodSelectorAttributes(methodInfo)这样的代码感觉由于缓存有关, 

复制代码代码如下:


private static ReadOnlyCollection<TAttribute> GetAttributes<TMemberInfo, TAttribute>(ConcurrentDictionary<TMemberInfo, ReadOnlyCollection<TAttribute>> lookup, TMemberInfo memberInfo) 
where TAttribute : Attribute 
where TMemberInfo : MemberInfo { 
return lookup.GetOrAdd(memberInfo, mi => new ReadOnlyCollection<TAttribute>((TAttribute[])memberInfo.GetCustomAttributes(typeof(TAttribute), inherit: true))); 


ReflectedAttributeCache这个类有几个缓存字典: 
ConcurrentDictionary<MethodInfo, ReadOnlyCollection<ActionMethodSelectorAttribute>> 
ConcurrentDictionary<MethodInfo, ReadOnlyCollection<ActionNameSelectorAttribute>> 
ConcurrentDictionary<MethodInfo, ReadOnlyCollection<FilterAttribute>> 
ConcurrentDictionary<Type, ReadOnlyCollection<FilterAttribute>> 
默认实现ActionMethodSelectorAttribute类主要有以下几个 
AcceptVerbsAttribute 
HttpDeleteAttribute 
HttpGetAttribute 
HttpPostAttribute 
HttpPutAttribute 
NonActionAttribute 
AcceptVerbsAttribute 
剩下的就是直接实例一个ReflectedActionDescriptor对象了,这个也没什么特殊,只是里面有一个验证方法 

复制代码代码如下:


if (validateMethod) { 
string failedMessage = VerifyActionMethodIsCallable(methodInfo); 
if (failedMessage != null) { 
throw new ArgumentException(failedMessage, "methodInfo"); 


用来验证该方法是否可以执行,以下几种情况经不会通过,(1)方法是静态方法(2)方法的实例类型不是ControllerBase(3)是否包含泛型参数如 public ActionResult Index<T>()是非法的,但 public ActionResult Index(List<string> aa)是合法(4)参数中不能含有Ref和out。 
这篇文章说的很散,我们需要注意一点微软在mvc里面缓存做的很好了,在前面个将获取ControllerTyper时它是有缓存的,一次读取当前程序集所有的ControllerType,在这里提到了一个DescriptorCache 缓存每次调用的ControllerType->ReflectedControllerDescriptor,而ReflectedControllerDescriptor实例会一次去读该Controller的所有Action方法;这里还有一个ReflectedAttributeCache,缓存每次调用MethodInfo的所有特性(ActionMethodSelectorAttribute、ActionNameSelectorAttribute、FilterAttribute),当然FilterAttribute特性还可以在类上面。

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