Ios NSAttributedStringKey提供未解析的标识符错误

我正在按照一个在线教程构建一个杂志类型的iOS应用程序。我正在尝试使用NSAttributedStringKey，但不断出现如下所示的错误。有什么想法吗

这是导致错误的代码行：

let attrs = [NSAttributedStringKey.foregroundColor: color, NSAttributedStringKey.font: font] as [NSAttributedStringKey : Any]

---

您尝试使用的代码是IOS11中添加的新API。因为您使用的是Xcode 8，所以您没有使用iOS 11。因此，您需要使用当前的（非测试版）API

---

您正在尝试在iOS 11之前的版本（可能是iOS 10）上使用iOS 11 API。惊讶的是，你发现一个教程已经使用测试版功能

同时，试试这个

let attrs=[NSForegroundColorAttributeName:color，NSFontAttributeName:font]

---

这应该行得通。

这个例子只适用于iOS11

import UIKit

class VC: UIViewController { 

    @IBOutlet weak var usernameTxt: UITextField!
    @IBOutlet weak var emailTxt: UITextField!
    @IBOutlet weak var passTxt: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        setupView()
    }

    func setupView() {
        usernameTxt.attributedPlaceholder = NSAttributedString(string: "username", attributes: [NSAttributedStringKey.foregroundColor: smackPurplePlaceholder])
        emailTxt.attributedPlaceholder = NSAttributedString(string: "email", attributes: [NSAttributedStringKey.foregroundColor: smackPurplePlaceholder])
        passTxt.attributedPlaceholder = NSAttributedString(string: "password", attributes: [NSAttributedStringKey.foregroundColor: smackPurplePlaceholder])  
    }    
}

---

这些项目可能有不同版本的Swift

在Swift 4中，NSFontAttributeName已替换为NSAttributedStringKey.font

如前所述

---

需要确认它是否能在低于ios11的版本上工作，Swift 4.1和Xcode 9.3更改属性键值

let strName = "Hello Stackoverflow"
let string_to_color2 = "Hello"        
let attributedString1 = NSMutableAttributedString(string:strName)
let range2 = (strName as NSString).range(of: string_to_color2)       
attributedString1.addAttribute(NSAttributedStringKey.foregroundColor, value: UIColor.red , range: range2)
lblTest.attributedText = attributedString1

---

Hello将以红色显示。

Swift 4.x

 // MARK: - Deal with the empty data set
// Add title for empty dataset
func title(forEmptyDataSet _: UIScrollView!) -> NSAttributedString! {
    let str = "Welcome"
    let attrs = [NSAttributedStringKey.font: UIFont.preferredFont(forTextStyle: UIFontTextStyle.headline)]
    return NSAttributedString(string: str, attributes: attrs)
}

// Add description/subtitle on empty dataset
func description(forEmptyDataSet _: UIScrollView!) -> NSAttributedString! {
    let str = "Tap the button below to add your first grokkleglob."
    let attrs = [NSAttributedStringKey.font: UIFont.preferredFont(forTextStyle: UIFontTextStyle.body)]
    return NSAttributedString(string: str, attributes: attrs)
}

// Add your image
func image(forEmptyDataSet _: UIScrollView!) -> UIImage! {
    return UIImage(named: "MYIMAGE")
}

// Add your button
func buttonTitle(forEmptyDataSet _: UIScrollView!, for _: UIControlState) -> NSAttributedString! {
    let str = "Add Grokkleglob"
    let attrs = [NSAttributedStringKey.font: UIFont.preferredFont(forTextStyle: UIFontTextStyle.callout), NSAttributedStringKey.foregroundColor: UIColor.white]
    return NSAttributedString(string: str, attributes: attrs)
}

// Add action for button
func emptyDataSetDidTapButton(_: UIScrollView!) {
    let ac = UIAlertController(title: "Button tapped!", message: nil, preferredStyle: .alert)
    ac.addAction(UIAlertAction(title: "Hurray", style: .default, handler: nil))
    present(ac, animated: true, completion: nil)
}

---

这是iOS11API。您看到的错误是什么？另外，您使用的是哪个版本的Swift/Xcode？@chrismanderson错误是“使用未声明的NSAttributedStringKey类型”Xcode版本-8.3.3。我认为这与版本问题有关，但不确定是否有解决方法等。Xcode9使用：[NSForegroundColorAttributeName:color]谢谢！这成功地消除了错误。但是，在教程之后，我没有收到显示的输出。我假设教程可能无法使用我的版本？教程-你应该找到一个不是基于新测试版和iOS 11的教程。这个问题与Swift版本无关。API更改是操作系统版本更改的结果。这一变化出现在iOS 11、macOS 10.13、tvOS 11.0和watchOS 4.0中。这一问题与Swift或Xcode的版本无关。API更改是操作系统版本更改的结果。iOS 11、macOS 10.13、tvOS 11.0和watchOS 4.0都发生了变化。

 // MARK: - Deal with the empty data set
// Add title for empty dataset
func title(forEmptyDataSet _: UIScrollView!) -> NSAttributedString! {
    let str = "Welcome"
    let attrs = [NSAttributedStringKey.font: UIFont.preferredFont(forTextStyle: UIFontTextStyle.headline)]
    return NSAttributedString(string: str, attributes: attrs)
}

// Add description/subtitle on empty dataset
func description(forEmptyDataSet _: UIScrollView!) -> NSAttributedString! {
    let str = "Tap the button below to add your first grokkleglob."
    let attrs = [NSAttributedStringKey.font: UIFont.preferredFont(forTextStyle: UIFontTextStyle.body)]
    return NSAttributedString(string: str, attributes: attrs)
}

// Add your image
func image(forEmptyDataSet _: UIScrollView!) -> UIImage! {
    return UIImage(named: "MYIMAGE")
}

// Add your button
func buttonTitle(forEmptyDataSet _: UIScrollView!, for _: UIControlState) -> NSAttributedString! {
    let str = "Add Grokkleglob"
    let attrs = [NSAttributedStringKey.font: UIFont.preferredFont(forTextStyle: UIFontTextStyle.callout), NSAttributedStringKey.foregroundColor: UIColor.white]
    return NSAttributedString(string: str, attributes: attrs)
}

// Add action for button
func emptyDataSetDidTapButton(_: UIScrollView!) {
    let ac = UIAlertController(title: "Button tapped!", message: nil, preferredStyle: .alert)
    ac.addAction(UIAlertAction(title: "Hurray", style: .default, handler: nil))
    present(ac, animated: true, completion: nil)
}