c# - Cannot create an editor in razor, System.Windows.Forms is needed

Question

I have this very basic form in ASP.NET:

@using (Html.BeginForm("Edit", "Home", FormMethod.Post))
{
    @Html.ValidationSummary(true)
    <fieldset>
        @Html.EditorFor(item => item.Name)
        <input type="submit" value="Upload" />
    </fieldset>
}

When I remove the line @Html.EditorFor(item => item.Name) everything works fine. But when I add it I get the following error:

FileNotFoundException: Could not load file or assembly 'System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

Why do I need Windows Forms in ASP??? Has anyone else ever experienced the same issue? I created a plain WebApplication with MVC in Rider. Target framework is netcoreapp3.1 and the language version is C# 8.0. If you need further details feel free to ask.

The entire callstack of the error is as follows:

System.IO.FileNotFoundException: Could not load file or assembly 'System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. File not found.
File name: 'System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'
   at System.Reflection.CustomAttribute._CreateCaObject(RuntimeModule pModule, RuntimeType type, IRuntimeMethodInfo pCtor, Byte** ppBlob, Byte* pEndBlob, Int32* pcNamedArgs)
   at System.Reflection.CustomAttribute.CreateCaObject(RuntimeModule module, RuntimeType type, IRuntimeMethodInfo ctor, IntPtr& blob, IntPtr blobEnd, Int32& namedArgs)
   at System.Reflection.CustomAttribute.AddCustomAttributes(ListBuilder`1& attributes, RuntimeModule decoratedModule, Int32 decoratedMetadataToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, ListBuilder`1 derivedAttributes)
   at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType)
   at System.Reflection.RuntimePropertyInfo.GetCustomAttributes(Type attributeType, Boolean inherit)
   at System.Attribute.InternalGetCustomAttributes(PropertyInfo element, Type type, Boolean inherit)
   at System.Attribute.GetCustomAttributes(MemberInfo element, Boolean inherit)
   at System.Reflection.CustomAttributeExtensions.GetCustomAttributes(MemberInfo element)
   at Microsoft.AspNetCore.Mvc.ModelBinding.ModelAttributes.GetAttributesForProperty(Type containerType, PropertyInfo property, Type modelType)
   at Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadataProvider.CreateSinglePropertyDetails(ModelMetadataIdentity propertyKey, PropertyHelper propertyHelper)
   at Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadataProvider.CreatePropertyDetails(ModelMetadataIdentity key)
   at Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadataProvider.GetMetadataForProperties(Type modelType)
   at Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadata.get_Properties()
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ExpressionMetadataProvider.FromLambdaExpression[TModel,TResult](Expression`1 expression, ViewDataDictionary`1 viewData, IModelMetadataProvider metadataProvider)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ModelExpressionProvider.CreateModelExpression[TModel,TValue](ViewDataDictionary`1 viewData, Expression`1 expression)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper`1.GetModelExpression[TResult](Expression`1 expression)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper`1.EditorFor[TResult](Expression`1 expression, String templateName, String htmlFieldName, Object additionalViewData)
   at Microsoft.AspNetCore.Mvc.Rendering.HtmlHelperEditorExtensions.EditorFor[TModel,TResult](IHtmlHelper`1 htmlHelper, Expression`1 expression)
   at AspNetCore.Views_Home_Edit.ExecuteAsync() in /my/path/Edit.cshtml:line 16
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ActionContext actionContext, IView view, ViewDataDictionary viewData, ITempDataDictionary tempData, String contentType, Nullable`1 statusCode)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewResultExecutor.ExecuteAsync(ActionContext context, ViewResult result)
   at Microsoft.AspNetCore.Mvc.ViewResult.ExecuteResultAsync(ActionContext context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

question from:https://stackoverflow.com/questions/65919585/cannot-create-an-editor-in-razor-system-windows-forms-is-needed

Answer 1

I've found the issue! I imported an enum from a file from another project where System.Windows.Forms was imported aswell. Moving the enum elsewhere solved the issue. Now I'm only importing stuff that doesn't import System.Windows.Forms.

If you happen to have the same problem: Check your imports, and the imports of your imports.