swift 通知中心使用未声明的类型名称错误

我遇到了最令人沮丧的错误。我正在我的应用程序中设置通知并使用 swift 4.2。我使用新语法。我设置的 popupController 设置如下

    NotificationCenter.default.post(name: .saveFoodGroup, object: self)
    dismiss(animated: true, completion: nil)

我创建了一个NotificationCenterExtension.swift包含名称的文件：

extension Notification.Name {
static let saveFoodGroup = Notification.Name(rawValue: "saveFoodGroup")
}

在我的控制器中，我将观察者设置.viewDidLoad()为如下：

NotificationCenter.default.addObserver(
  forName: .saveFoodGroup,
  object: nil,
  queue: OperationQueue.main ) {
     (notification) in
         let groupPopUp = notification.object as! ScalePopUpController
         print(groupPopUp)
         self.foodGroup = groupPopUp.textInput as? String
   }

但是在运行时我不断收到此错误：

unrecognised selector sent to instance 0x7fb9c7e23ef0'

经过一番搜索，我发现当 #selectors 设置不正确时，这是一个旧的 ObjC 错误。但由于我使用的是新语法，这应该不是问题。最后一条线索：当我将鼠标悬停.saveFoodGroup在NotificatioCenter.default.post(name: .saveFoodGroup) 调用中的参数上时；我得到了这个神秘的提示；expression produced error: error:

/var/folders/xj/f18tylg51kl33z6c6p2vh34r0000gn/T/expr15-a14342..swift:1:65: 错误：使用未声明的类型“名称”

谁能告诉我这是怎么回事？

完整的错误信息：

2018-12-04 20:17:28.780056+0100 unFatMobile[47399:4108185] -[unFatMobile.ScalePopUpController onBtPRew:]: unrecognized selector sent to instance 0x7fb9c7e23ef0
2018-12-04 20:17:28.787522+0100 unFatMobile[47399:4108185] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[unFatMobile.ScalePopUpController onBtPRew:]: unrecognized selector sent to instance 0x7fb9c7e23ef0'

(
0   CoreFoundation                      0x000000010c6b91bb __exceptionPreprocess + 331
1   libobjc.A.dylib                     0x000000010a6d3735 objc_exception_throw + 48
2   CoreFoundation                      0x000000010c6d7f44 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
3   UIKitCore                           0x000000010f091b4a -[UIResponder doesNotRecognizeSelector:] + 287
4   CoreFoundation                      0x000000010c6bded6 ___forwarding___ + 1446
5   CoreFoundation                      0x000000010c6bfda8 _CF_forwarding_prep_0 + 120
6   UIKitCore                           0x000000010f064ecb -[UIApplication sendAction:to:from:forEvent:] + 83
7   UIKitCore                           0x000000010eaa00bd -[UIControl sendAction:to:forEvent:] + 67
8   UIKitCore                           0x000000010eaa03da -[UIControl _sendActionsForEvents:withEvent:] + 450
9   UIKitCore                           0x000000010ea9f31e -[UIControl touchesEnded:withEvent:] + 583
10  UIKitCore                           0x000000010f0a00a4 -[UIWindow _sendTouchesForEvent:] + 2729
11  UIKitCore                           0x000000010f0a17a0 -[UIWindow sendEvent:] + 4080
12  UIKitCore                           0x000000010f07f394 -[UIApplication sendEvent:] + 352
13  UIKit                               0x0000000127f0b183 -[UIApplicationAccessibility sendEvent:] + 85
14  UIKitCore                           0x000000010f1545a9 __dispatchPreprocessedEventFromEventQueue + 3054
15  UIKitCore                           0x000000010f1571cb __handleEventQueueInternal + 5948
16  CoreFoundation                      0x000000010c61e721 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
17  CoreFoundation                      0x000000010c61df93 __CFRunLoopDoSources0 + 243
18  CoreFoundation                      0x000000010c61863f __CFRunLoopRun + 1263
19  CoreFoundation                      0x000000010c617e11 CFRunLoopRunSpecific + 625
20  GraphicsServices                    0x00000001147d41dd GSEventRunModal + 62
21  UIKitCore                           0x000000010f06381d UIApplicationMain + 140
22  unFatMobile                         0x0000000109d56f47 main + 71
23  libdyld.dylib                       0x000000010db52575 start + 1
)