title: How to change the properties from one ViewController's function?
body: <p>I have two Controller which names are <code>FirstViewController</code> and <code>SecondViewController</code></p>
  
  <p>the <code>FirstViewController</code> is the MainPage and I add a <code>UITextView</code> here.</p>
  
  <pre><code>var secondViewController: SecondViewController!
  
  let textView: UITextView = {
      let textView = UITextView()
      //textView.font = UIFont.systemFont(ofSize: 20)
      textView.isEditable = true
      textView.keyboardDismissMode = .interactive
      textView.allowsEditingTextAttributes = true
      return textView
  }()
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      secondViewController = SecondViewController()
  
      setUpLayout() //do something like add the textView to the view
      addKeyboardObserver() //a function which observe the keyboard
  }
  </code></pre>
  
  <p>then I add a button to show secondView as a keyboard</p>
  
  <pre><code>@objc func showSecondView() {
      textView.resignFirstResponder()
      textView.inputView = secondViewController.view
      textView.becomeFirstResoonder()
  }
  </code></pre>
  
  <p>then I define a function to close the secondView</p>
  
  <pre><code>func closeSecondView() {
      textView.resignFirstResponder()
      textView.inputView = nil
  }
  </code></pre>
  
  <p>in my <code>SecondViewController</code></p>
  
  <pre><code>var firstViewController: FirstViewController!
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      firstViewController = FirstViewController()
  
      self.view.frame = CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: 300)
      self.view.backgroundColor = .cyan
  }
  </code></pre>
  
  <p>then I add a button to close the firstViewController's custom keyboard</p>
  
  <pre><code>@objc func closeFontView() {
      print(123)
      firstViewController.closeSecondView()
  }
  </code></pre>
  
  <p>the result is, "123" is printed, then I add a breakpoint at <code>closeFontView()</code>, it is called. but the change of UI isn't show up.(the keyboard is not be closed) Why? how can I fix that?</p>