swift - 在 Swift 中从 userInfo 获取键盘大小

Question

我一直在尝试添加一些代码，以便在键盘出现时向上移动我的 View ，但是，我在尝试将 Objective-C 示例转换为 Swift 时遇到了问题。我取得了一些进展，但我被困在一条特定的线上。

这是我一直关注的两个教程/问题:

How to move content of UIViewController upwards as Keypad appears using Swift http://www.ioscreator.com/tutorials/move-view-when-keyboard-appears

这是我目前拥有的代码:

override func viewWillAppear(animated: Bool) {
    NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillShow:", name: UIKeyboardWillShowNotification, object: nil)
    NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillHide:", name: UIKeyboardWillHideNotification, object: nil)
}

override func viewWillDisappear(animated: Bool) {
    NSNotificationCenter.defaultCenter().removeObserver(self)
}

func keyboardWillShow(notification: NSNotification) {
    var keyboardSize = notification.userInfo(valueForKey(UIKeyboardFrameBeginUserInfoKey))
    UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)
    let frame = self.budgetEntryView.frame
    frame.origin.y = frame.origin.y - keyboardSize
    self.budgetEntryView.frame = frame
}

func keyboardWillHide(notification: NSNotification) {
    //
}

目前，我在这一行遇到错误:

var keyboardSize = notification.userInfo(valueForKey(UIKeyboardFrameBeginUserInfoKey))

如果有人能让我知道这行代码应该是什么，我应该设法自己弄清楚其余部分。

Answer 1

你的线路有一些问题:

var keyboardSize = notification.userInfo(valueForKey(UIKeyboardFrameBeginUserInfoKey))

• notification.userInfo 返回一个可选字典[NSObject : AnyObject]?, 因此在访问其值之前必须对其进行解包。
• Objective-C NSDictionary 映射到 Swift 原生字典，所以你必须 使用字典下标语法 (dict[key]) 访问值。
• 该值必须转换为 NSValue，以便您可以对其调用 CGRectValue。

所有这些都可以通过可选赋值、可选链接和可选强制转换的组合来实现:

if let userInfo = notification.userInfo {
   if let keyboardSize = (userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.CGRectValue() {
    let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)
       // ...
   } else {
       // no UIKeyboardFrameBeginUserInfoKey entry in userInfo
   }
} else {
   // no userInfo dictionary in notification
}

或者一步到位:

if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.CGRectValue() {
    let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)
    // ...
}

Swift 3.0.1 (Xcode 8.1) 更新:

if let userInfo = notification.userInfo {
    if let keyboardSize = userInfo[UIKeyboardFrameBeginUserInfoKey] as? CGRect {
        let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)
        // ...
    } else {
        // no UIKeyboardFrameBeginUserInfoKey entry in userInfo
    }
} else {
    // no userInfo dictionary in notification
}

或者一步到位:

if let keyboardSize = notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? CGRect {
    let contentInsets = UIEdgeInsets(top: 0, left: 0, bottom: keyboardSize.height, right: 0)
    // ...
}

Swift 5 (Xcode 11.6) 更新:

 guard let userInfo = notification.userInfo,
              let keyboardSize = userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect else { return }

我建议使用 keyboardFrameEndUserInfoKey 而不是 keyboardFrameBeginUserInfoKey，因为键盘会在旧版 iOS 设备上首次显示后更改初始渲染高度。