Custom ViewEngine using Razor engine to select Masterpage dynamically - asp.net-mvc-3

Question

I´m trying to create my Custom ViewEngine with Razor...
My code is based on jfar post, the only difference I´m using Razor engine...
I have 2 "masterpages" :
_Admin.cshtml
_Modal.cshtml
And the FindView method from my custom ViewEngine :
public override ViewEngineResult FindView(ControllerContext controllerContext, string viewName, string masterName, bool useCache)
{
if (controllerContext.HttpContext.Request.IsAjaxRequest())
return base.FindView(controllerContext, viewName, "_Modal", useCache);
return base.FindView(controllerContext, viewName, "_Admin", useCache);
}
Debugging that, the ViewEngineResult.View is always null, and the generated view is always the same, no matter the masterpage...
If I force usecache = false, it returns the view, but I got that error:
The view at '~/Views/Car/Index.cshtml'
must derive from ViewPage,
ViewPage, ViewUserControl, or
ViewUserControl.
[InvalidOperationException: The view at '~/Views/Car/Index.cshtml' must derive from ViewPage, ViewPage<TModel>, ViewUserControl, or ViewUserControl<TModel>.]
System.Web.Mvc.WebFormView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) +306227
System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) +115
System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +303
System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +13
System.Web.Mvc.<>c__DisplayClass1c.<InvokeActionResultWithFilters>b__19() +23
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +260
System.Web.Mvc.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b() +19
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +260
System.Web.Mvc.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b() +19
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +260
System.Web.Mvc.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b() +19
System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +177
System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +343
System.Web.Mvc.Controller.ExecuteCore() +116
System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +97
System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +10
System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +37
System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +21
System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12
System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62
System.Web.Mvc.<>c__DisplayClasse.<EndProcessRequest>b__d() +50
System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +7
System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +22
System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +60
System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8841105
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184
Any help?
Thanks

Answer 1

The problem is that you are using a single cache for 2 different kinds of requests. While it does not directly address your question, take a look at the following post that discusses a similar problem: http://www.hanselman.com/blog/ABetterASPNETMVCMobileDeviceCapabilitiesViewEngine.aspx
For the exception, could you post the stack trace?