【Swift】カスタムキーボードが表示されない

前提・実現したいこと

Swift初心者です。
raywenderrich.comの記事を参考にさせて頂きながらカスタムキーボードを開発中です。

発生している問題・エラーメッセージ

参考にさせて頂いているraywenderlich.comの記事のStarterファイルをビルドしてみたのですが、下図のように何も表示されず、エラーが出てしまいました。新たに作成したカスタムキーボード拡張機能のSwiftファイル（keyboardviewcontroller.swift）と連携ができていないのかもしれないです。どなたかご回答して頂きたいです。下にファイル構成のスクショも貼っておきます。

MorseKeyboard[59137:6509431] [External] -[UIInputViewController needsInputModeSwitchKey] was called before a connection was established to the host application. This will produce an inaccurate result. Please make sure to call this after your primary view controller has been initialized.

keyboardviewcontroller.swift

swift
1/// Copyright (c) 2021 Razeware LLC
2/// 
3/// Permission is hereby granted, free of charge, to any person obtaining a copy
4/// of this software and associated documentation files (the "Software"), to deal
5/// in the Software without restriction, including without limitation the rights
6/// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
7/// copies of the Software, and to permit persons to whom the Software is
8/// furnished to do so, subject to the following conditions:
9/// 
10/// The above copyright notice and this permission notice shall be included in
11/// all copies or substantial portions of the Software.
12/// 
13/// Notwithstanding the foregoing, you may not use, copy, modify, merge, publish,
14/// distribute, sublicense, create a derivative work, and/or sell copies of the
15/// Software in any work that is designed, intended, or marketed for pedagogical or
16/// instructional purposes related to programming, coding, application development,
17/// or information technology.  Permission for such use, copying, modification,
18/// merger, publication, distribution, sublicensing, creation of derivative works,
19/// or sale is expressly withheld.
20/// 
21/// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
22/// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
23/// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
24/// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
25/// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
26/// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
27/// THE SOFTWARE.
28
29import UIKit
30
31class KeyboardViewController: UIInputViewController {
32
33    @IBOutlet var nextKeyboardButton: UIButton!
34    
35    override func updateViewConstraints() {
36        super.updateViewConstraints()
37        
38        // Add custom view sizing constraints here
39    }
40    
41    override func viewDidLoad() {
42        super.viewDidLoad()
43        
44        // Perform custom UI setup here
45        self.nextKeyboardButton = UIButton(type: .system)
46        
47        self.nextKeyboardButton.setTitle(NSLocalizedString("Next Keyboard", comment: "Title for 'Next Keyboard' button"), for: [])
48        self.nextKeyboardButton.sizeToFit()
49        self.nextKeyboardButton.translatesAutoresizingMaskIntoConstraints = false
50        
51        self.nextKeyboardButton.addTarget(self, action: #selector(handleInputModeList(from:with:)), for: .allTouchEvents)
52        
53        self.view.addSubview(self.nextKeyboardButton)
54        
55        self.nextKeyboardButton.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
56        self.nextKeyboardButton.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
57    }
58    
59    override func viewWillLayoutSubviews() {
60        self.nextKeyboardButton.isHidden = !self.needsInputModeSwitchKey
61        super.viewWillLayoutSubviews()
62    }
63    
64    override func textWillChange(_ textInput: UITextInput?) {
65        // The app is about to change the document's contents. Perform any preparation here.
66    }
67    
68    override func textDidChange(_ textInput: UITextInput?) {
69        // The app has just changed the document's contents, the document context has been updated.
70        
71        var textColor: UIColor
72        let proxy = self.textDocumentProxy
73        if proxy.keyboardAppearance == UIKeyboardAppearance.dark {
74            textColor = UIColor.white
75        } else {
76            textColor = UIColor.black
77        }
78        self.nextKeyboardButton.setTitleColor(textColor, for: [])
79    }
80
81}
82