Question

我有一个ASP.NET MVC 2应用程序，我在其中创建自定义操作过滤器。此过滤器位于应用程序中的控制器上，并从数据库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，根据请求的操作，我需要将用户重定向到返回视图，部分视图或JSON的操作。

根据ActionExecutingContext，我可以找出最初请求的操作的返回类型是什么吗？

编辑：

好的，我越来越近但又有另一个问题。

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动作方法的返回类型。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

我收到了一个AmbiguousMatchException。

根据OnActionExecuting方法中的信息，无论如何都要确定正在调用的重载更精确吗？

Answer 1

我基于此创建了一个AuthenticationFilterAttribute，它根据类型返回不同的结果：

    /// <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;
        }
    }

Answer 2

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（string）调用无法识别请求的方法，我将从ActionExecutingContext.ActionParameters集合中获取参数集合，并构建请求中传递的参数类型的数组。然后，我可以使用Type.GetMethod（string，type（））重载来更具体地说明我的请求。

Answer 3

当调用OnActionExecuting时，操作方法尚未执行，因此您无法知道该操作方法是否将返回ActionResult的哪个子类。所以，除非你可以使用CIL分析实现（我觉得很快就会变丑），我不认为你想做什么是可能的。

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

Answer 4

上面有一些不错的答案，但在 MVC Core 中，我注意到您可以通过强制转换为 ControllerActionDescriptor 来获取方法信息，这会清除上面的一些答案。 （我在预览版 6 的 Blazor Webassembly Web Api 后端中使用它）

((Microsoft.AspNetCore.Mvc.Controllers.ControllerActionDescriptor)filterContext.ActionDescriptor).MethodInfo

因此获取返回类型可能会变成：

public static class FilterHelper
{
    public static Type GetReturnType(this ActionExecutingContext filterContext)
    {
        return ((ControllerActionDescriptor)filterContext.ActionDescriptor).MethodInfo.ReturnType;

    }
}

并像这样使用：

Type t = actionContext.GetReturnType();

将更新为 6 Preview 的完整解决方案

我可以从动作过滤器中获取Action的返回类型吗？

4 个答案: