在 Swift 中从 userInfo 获取键盘大小 [英] Getting keyboard size from userInfo in Swift

问题描述

我一直在尝试添加一些代码以在键盘出现时向上移动我的视图，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，但我被困在一个特定的行上.

I have been trying to add some code to move my view up when the keyboard appears, however, I am having issues trying to translate the Objective-C examples into Swift. I have made some progress, but I am stuck on one particular line.

这是我一直在关注的两个教程/问题:

These are the two tutorials/questions I have been following:

如何移动使用 Swift 出现键盘时 UIViewController 向上http://www.ioscreator.com/tutorials/move-view-when-键盘出现

这是我目前拥有的代码:

Here is the code I currently have:

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:

At the moment, I am getting an error on this line:

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的.

If someone could let me know what this line of code should be, I should manage to figure out the rest myself.

推荐答案

您的线路存在一些问题:

There are some problems in your line:

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

• notification.userInfo 返回一个可选字典[NSObject : AnyObject]?，所以在访问它的值之前它必须被解包.
• 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.
• 必须将该值转换为 NSValue，以便您可以对其调用 CGRectValue.
• notification.userInfo returns an optional dictionary [NSObject : AnyObject]?, so it must be unwrapped before accessing its values.
• The Objective-C NSDictionary is mapped to a Swift native Dictionary, so you must use the dictionary subscript syntax (dict[key]) to access the values.
• The value must be cast to NSValue so that you can call CGRectValue on it.

所有这些都可以通过结合可选赋值、可选链和可选强制转换来实现:

All this can be achieved with a combination of optional assignment, optional chaining and optional casts:

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:

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) 的更新:

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:

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) 的更新:

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

我建议使用 keyboardFrameEndUserInfoKey 而不是 keyboardFrameBeginUserInfoKey 因为键盘会在较旧的 iOS 设备上首次显示后更改初始渲染高度.

I recommend using keyboardFrameEndUserInfoKey instead of keyboardFrameBeginUserInfoKey since the keyboard changes the initial render height after the first display on older iOS devices.

这篇关于在 Swift 中从 userInfo 获取键盘大小的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！