ios - becomeFirstResponder 后不会立即调用 keyboardWillShow 通知

Question

我已经实现了 keyboardWillShow: 和 keyboardWillHide: 通知。我正在注册通知，在直接触摸 UITextField 上的屏幕后它们可以正常工作，但是有一个问题。在我的 viewDidLoad 中，注册通知后立即调用 becomeFirstResponder。键盘弹出，但 keyboardWillShow: 没有被调用(如前所述，只是第一次。从您调用该函数注册通知的时间到它被调用的时间似乎有延迟实际上已经注册了，我不应该延迟 becomeFirstResponder 的执行)。有什么想法吗？

@objc func keyboardWillShow(_ notification: NSNotification) {
    print("Show")
    if let keyboardSize = (notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue {
        var userInfo = notification.userInfo!
        var keyboardFrame:CGRect = (userInfo[UIKeyboardFrameBeginUserInfoKey] as! NSValue).cgRectValue
        keyboardFrame = self.view.convert(keyboardFrame, from: nil)
        var contentInset: UIEdgeInsets = self.tv_main.contentInset
        contentInset.bottom = keyboardSize.height
        self.tv_main.contentInset = contentInset
        let indexpath = IndexPath(row: 0, section: 0)
        self.tv_main.scrollToRow(at: indexpath, at: UITableViewScrollPosition.top, animated: true)
    }
}

@objc func keyboardWillHide(_ notification: NSNotification) {
    print("Hide")
    if let _ = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue {
        let contentInset:UIEdgeInsets = UIEdgeInsets.zero
        self.tv_main.contentInset = contentInset

    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    tv_main.delegate = self
    tv_main.dataSource = self
    tf_search.delegate = self
    NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillHide), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
    self.tf_search.becomeFirstResponder()
    if let placeholder = tf_search.placeholder {
        tf_search.attributedPlaceholder = NSAttributedString(string:placeholder, attributes: [NSAttributedStringKey.foregroundColor: UIColor.white])
    }
}

Answer 1

您应该在 viewWillAppear 或 viewDidAppear 中调用 becomeFirstResponder。