Question

这是整个应用程序的代码。只需在情节提要板上添加UITextField并点击它即可。您将打印“ AAAA”。然后点击键盘上的任意键。它将再次打印“ AAAA”。

为什么在这种情况下第二次触发UIResponder.keyboardDidShowNotification通知？我该如何预防？

keyboardWillShowNotification的行为相同：（

代码：

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        addKeyboardObservers(to: .default)
    }

    func addKeyboardObservers(to notificationCenter: NotificationCenter) {
          notificationCenter.addObserver(
              forName: UIResponder.keyboardDidShowNotification,
              object: nil,
              queue: OperationQueue.main,
              using: { _ in
                    print("AAAA")
              }
          )
    }
}

与Harish的代码相同：

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.addObserver(
          self,
          selector: #selector(keyboardWasShown),
          name: UIWindow.keyboardDidShowNotification,
          object: nil)
    }

    @objc func keyboardWasShown(_ notification: NSNotification) {
        print("AAA")
    }

}

Answer 1

为什么不在下面使用？

class ViewController: UIViewController {

  override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(
      self,
      selector: #selector(keyboardWasShown),
      name: UIWindow.keyboardDidShowNotification,
      object: nil)
  }

  @objc func keyboardWasShown(_ notification: NSNotification) {

  }
}

敲击键盘键后会触发keyboardDidShowNotification和keyboardWillShowNotification

1 个答案: