我可以从动作过滤器中获取动作的返回类型吗？

Question

我有一个 ASP.NET MVC 2 应用程序，我正在其中创建一个自定义操作过滤器。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。

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

编辑：

好的，我越来越近了，但还有一个问题。

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

我可以使用反射来找到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

我得到一个 AmbiguousMatchException 抛出。

根据我在 OnActionExecuting 方法中的信息，是否可以更准确地确定正在调用的重载？

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，这就是我想出的解决方案。

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

到OnActionExecuting 被调用时，action 方法还没有被执行，所以你无法知道action 方法是否会返回ActionResult 的哪个子类。因此，除非您可以使用 CIL 分析实现（我认为这会很快变得丑陋），否则我认为您想要做的事情是不可能的。

也就是说，当控制器不够可用时，您是否将用户重定向到视图？我的意思是，我不明白您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，但是在 MVC Core 中，我注意到您可以通过转换为 ControllerActionDescriptor 来获取方法信息，这将清除上面的一些答案。 （我在 Preview 6 的 Blazor Webassembly Web Api 后端使用它）

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

所以获取返回类型可能变成：

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

    }
}

并且可以像这样使用：

Type t = actionContext.GetReturnType();

将更新 6 Preview 的完整解决方案