我可以从Action Filter获取Action的返回类型吗？

Question

我有一个ASP.NET MVC 2应用程序，我在其中创建自定义操作筛选器。此过滤器位于应用程序中的控制器上，并从数据库中验证该功能当前是否可用。

Public Overrides Sub OnActionExecuting(ByVal filterContext As System.Web.Mvc.ActionExecutingContext) 
    Try 
    ' Check controller name against database. 
    Dim controllerName = filterContext.Controller.GetType().Name 
    controllerName = controllerName.Remove(controllerName.Length - 10) 
    ' Look up availability. 
    Dim available As Boolean = _coreService.GetControllerAvailability(controllerName) 
    If Not available Then 
     ' Redirect to unavailable notice. 
     filterContext.Result = New RedirectResult("/Home/Unavailable/") 
    End If 
    Catch ex As Exception 
    _eventLogger.LogWarning(ex, EventLogEntryType.Error) 
    Throw 
    End Try 
End Sub 

我的问题是，根据已请求的操作，我需要将用户重定向到返回一个视图，局部视图或JSON的动作。

鉴于ActionExecutingContext我可以找出最初请求的动作的返回类型是什么？编辑：

好吧，我越来越近，但有另一个问题。

Public Overrides Sub OnActionExecuting(ByVal filterContext As System.Web.Mvc.ActionExecutingContext) 
    Try 
    ' Check controller name against database. 
    Dim controllerName = filterContext.Controller.GetType().Name 
    Dim shortName = controllerName.Remove(controllerName.Length - 10) 
    ' Look up availability. 
    Dim available As Boolean = _coreService.GetControllerAvailability(shortName) 
    If Not available Then 
     ' find out what type is expected to be returned 
     Dim actionName As String = filterContext.ActionDescriptor.ActionName 
     Dim controllerType = Type.GetType("Attenda.Stargate.Web." & controllerName) 
     Dim actionMethodInfo = controllerType.GetMethod(actionName) 
     Dim actionReturnType = actionMethodInfo.ReturnType.Name 

     Select Case actionReturnType 
     Case "PartialViewResult" 
      filterContext.Result = New RedirectResult("/Home/UnavailablePartial/") 
     Case "JsonResult" 
      filterContext.Result = New RedirectResult("/Home/UnavailableJson/") 
     Case Else 
      filterContext.Result = New RedirectResult("/Home/Unavailable/") 
     End Select 

    End If 
    Catch ex As Exception 
    _eventLogger.LogWarning(ex, EventLogEntryType.Error) 
    Throw 
    End Try 
End Sub 

我可以使用反射来查找操作方法的返回类型。我的问题是如果我在控制器上有以下方法：

Public Function Create() As ViewResult 
    Return View() 
End Function 

<AcceptVerbs(HttpVerbs.Post)> 
Public Function Create(values as FormCollection) As ViewResult 
    ' Do stuff here 
End Function 

我得到一个AmbiguousMatchException抛出。

有了OnActionExecuting方法中的信息，是否有更精确的方法来确定被调用的过载？

Answer 1

好的，这是我提出的解决方案。

Public Overrides Sub OnActionExecuting(ByVal filterContext As System.Web.Mvc.ActionExecutingContext) 
    Try 
    ' Check controller name against database. 
    Dim controllerName = filterContext.Controller.GetType().Name 
    Dim shortName = controllerName.Remove(controllerName.Length - 10) 
    ' Look up availability. 
    Dim available As Boolean = _coreService.GetControllerAvailability(shortName) 
    If Not available Then 
     ' find out what type is expected to be returned 
     Dim actionName As String = filterContext.ActionDescriptor.ActionName 
     Dim controllerType = Type.GetType("Attenda.Stargate.Web." & controllerName) 
     Dim actionMethodInfo As MethodInfo 
     Try 
     actionMethodInfo = controllerType.GetMethod(actionName) 
     Catch ex As AmbiguousMatchException 
     ' Try to find a match using the parameters passed through 
     Dim actionParams = filterContext.ActionParameters 
     Dim paramTypes As New List(Of Type) 
     For Each p In actionParams 
      paramTypes.Add(p.Value.GetType()) 
     Next 
     actionMethodInfo = controllerType.GetMethod(actionName, paramTypes.ToArray) 
     End Try 
     Dim actionReturnType = actionMethodInfo.ReturnType.Name 

     Select Case actionReturnType 
     Case "PartialViewResult" 
      filterContext.Result = New RedirectResult("/Home/UnavailablePartial/") 
     Case "JsonResult" 
      filterContext.Result = New RedirectResult("/Home/UnavailableJson/") 
     Case Else 
      filterContext.Result = New RedirectResult("/Home/Unavailable/") 
     End Select 

    End If 
    Catch ex As Exception 
    _eventLogger.LogWarning(ex, EventLogEntryType.Error) 
    Throw 
    End Try 
End Sub 

如果Type.GetMethod（字符串）调用失败识别方法要求，我取从ActionExecutingContext.ActionParameters集合的参数集合，并建立类型在请求中传递的参数的阵列。然后，我可以使用Type.GetMethod（string，type（））重载来更具体地了解我的请求。

Answer 2

在调用OnActionExecuting时，action方法尚未执行，因此无法知道该操作方法是否要返回ActionResult的哪个子类。所以，除非你能够使用CIL分析实现（我认为它可能会很快变得丑陋），否则我不认为你想要做什么是可能的。

这就是说，当控制器不够用时，您是不是将用户重定向到视图？我的意思是，我不明白你为什么要将用户重定向到JSON结果或部分视图。

Answer 3

我创建了一个基于此，它返回根据类型的不同结果的AuthenticationFilterAttribute：

/// <summary> 
    /// Access to the action will be blocked if the user is not logged in. 
    /// Apply this to the controller level or individual actions as an attribute. 
    /// </summary> 
    public class AuthenticationFilterAttribute : ActionFilterAttribute 
    { 
     protected const string InvalidAccess = "Invalid access"; 

     public override void OnActionExecuting(ActionExecutingContext filterContext) 
     { 
      // Find out if the user is logged in: 
      Controller controller = (Controller)filterContext.Controller; 
      if (!controller.User.Identity.IsAuthenticated) 
      { 
       switch (GetExpectedReturnType(filterContext).Name) 
       { 
        case "JsonResult": 
         var jsonResult = new JsonResult(); 
         jsonResult.Data = new { Error = true, ErrorMessage = InvalidAccess }; 
         jsonResult.JsonRequestBehavior = JsonRequestBehavior.AllowGet; 
         filterContext.Result = jsonResult; 
         break; 

        // Assume same behaviour as ActionResult 
        default: 
         var actionResult = new ContentResult(); 
         actionResult.Content = InvalidAccess; 
         filterContext.Result = actionResult; 
         break; 
       } 
      } 
     } 

     private Type GetExpectedReturnType(ActionExecutingContext filterContext) 
     { 
      // Find out what type is expected to be returned 
      string actionName = filterContext.ActionDescriptor.ActionName; 
      Type controllerType = filterContext.Controller.GetType(); 
      MethodInfo actionMethodInfo = default(MethodInfo); 
      try 
      { 
       actionMethodInfo = controllerType.GetMethod(actionName); 
      } 
      catch (AmbiguousMatchException ex) 
      { 
       // Try to find a match using the parameters passed through 
       var actionParams = filterContext.ActionParameters; 
       List<Type> paramTypes = new List<Type>(); 
       foreach (var p in actionParams) 
       { 
        paramTypes.Add(p.Value.GetType()); 
       } 

       actionMethodInfo = controllerType.GetMethod(actionName, paramTypes.ToArray()); 
      } 

      return actionMethodInfo.ReturnType; 
     } 
    }